Stable isotope ecology

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    A review of stable hydrogen and oxygen isotopic offset in plant water source research
    LEI Zi-Ran, JIA Guo-Dong, YU Xin-Xiao, LIU Zi-He
    Chin J Plant Ecol    2023, 47 (1): 25-40.   DOI: 10.17521/cjpe.2021.0479
    Accepted: 09 June 2022

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    Stable hydrogen and oxygen isotope analysis provides an important tool for calculating plant root water uptake amount, determining the contribution to plant water source, and evaluating plant water use strategy, and is thus of great relevance to ecohydrological studies with respect to exploration of the water transmission mechanism of the atmosphere-vegetation-soil system. However, the stable hydrogen and oxygen isotope ratios (δ2H and δ18O) offset between soil and xylem water can cause inconsistency in the calculated contribution rate of plant water source, but the reasons for differences in hydrogen and oxygen isotope results are unclear. In this review, we first briefly introduced the phenomenon of hydrogen-oxygen stable isotope ratio offset; secondly, the framework was constructed along the water transport path of the soil-plant-atmosphere continuum. We systematically expounded the natural effects of δ2H and δ18O offset in three interfaces (plant-atmosphere interface, soil-atmosphere interface, and root-soil interface) and two spaces (plant and soil layer). At the same time, we summarized the methodological artifacts that are associated with soil and xylem sample extraction and δ2H and δ18O determination technologies. Finally, we identify main knowledge uncertainties according to the existing research progress; and highlight three areas that deserve future research attention: the acquisition of isotope spatiotemporal data, the cause of micro-scale isotope offset, and the optimization of extraction and determination technology.

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    Progress in the theory, hypothesis and application of the methods measuring soil CO2 flux gradient
    WANG Jing-Yuan, WEI Jie, WEN Xue-Fa
    Chin J Plant Ecol    2022, 46 (12): 1523-1536.   DOI: 10.17521/cjpe.2021.0427
    Accepted: 17 October 2022

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    Soil respiration is mainly composed of the CO2 released from atmosphere-soil interface and change of CO2 stored in the soil. Understanding the production and migration of CO2 in the soil is essential for measuring the carbon cycle in terrestrial ecosystems. The flux gradient method calculates soil CO2 flux by measuring the diffusion-driven CO2 concentration gradient and diffusion coefficient. The flux of soil CO2 and its stable carbon isotopes composition (δ13C) at different depths can be calculated based on Fickʼs law. The amount of CO2 released from soil and the amount of CO2 stored in different soil layers can thus be measured. The underground soil CO2 (13CO2 and 12CO2) concentration is mainly controlled by pore tortuosity, the depth of root distribution, microbial activity and total soil CO2 production. The underground CO2 transmission process is mainly controlled by the CO2 concentrations, porosity and water content at different depths of the soil. These physical, chemical and biological features of the soil are key factors affecting the application of the soil flux gradient method, and directly determine the precision and accuracy of soil CO2 and its δ13C flux calculation. The gradient method is a useful complement to the chamber method, which can clarify the process of production and migration of soil CO2 at different depths and thus the impacts on the release and storage of soil CO2, elucidating the contribution of soils at different depths to CO2 release and uncovering the underlying environmental and physical mechanisms.

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    Effects of different water isotope input methods based on Bayesian model MixSIAR on water uptake characteristic analysis results in apple orchards
    LU Chen-Xi, XU Man, SHI Xue-Jin, ZHAO Cheng, TAO Ze, LI Min, SI Bing-Cheng
    Chin J Plant Ecol    2023, 47 (2): 238-248.   DOI: 10.17521/cjpe.2021.0472
    Accepted: 15 July 2022

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    Aims Accurately quantifying the contribution of shallow, middle and deep soil water sources to the root water uptake is the prerequisite for understanding water uptake strategy of plants. This paper evaluates the effects of different water isotopes input methods on plant water sources analysis results in Bayesian mixing model MixSIAR.

    Methods Soil and plant xylem samples were taken five times from May to September in 2019 in two apple (Malus pumila) orchards at 7- and 18-year age in Changwu Tableland of Shaanxi Province. Soil water contents and isotope ratios (δ2H and δ18O) were measured, and the different input methods of single isotope (2H and 18O), dual isotopes (2H & 18O) and xylem hydrogen corrected dual isotopes (2H(+8.1) & 18O) coupled with MixSIAR model were used to estimate the contribution ratio of different soil layers (0-0.4, 0.4-2, >2 m root depth) to orchards root water uptake.

    Important findings The results showed that compared to the 2H isotope method, the contribution from soil layer below 2 m was lower and that from the surface 0-0.4 m was higher using the 18O isotope method, which was close to the 2H(+8.1) & 18O isotope method. Compared with 2H & 18O dual isotopes method, the contribution ratio from surface 0-0.4 m soil layer was higher using the 2H(+8.1) & 18O method when the surface soil water isotope was enriched, and that was lower when the surface soil water isotope was depleted. The corrected apple xylem hydrogen isotopes were closer to the evaporation line of soil water isotopes, thus the analysis methods of 18O and 2H(+8.1) & 18O accorded more with the isotope mass balance during root water uptake than 2H and 2H & 18O methods. Soil water contents in 0-2 m in 18 years old apple orchard showed greater seasonal variation than that in 7 years old apple orchard, and are more dependent on 0-0.4 m surface soil water. For the root water uptakes in 7- and 18-year apple orchard, the yearly-averaged contributions of deep soil water were 19% and 23%, respectively, showing no significant difference. We suggest that more attention should be drawn on the influence of different isotope input methods when using water stable isotopes to estimate plant water sources contribution in future studies.

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    Foliar assimilation and distribution of NO2 in Schima superba and Pinus massoniana seedlings using 15N stable isotope tracing technique
    YAO Meng, KANG Rong-Hua, WANG Ang, MA Fang-Yuan, LI Jin, TAI Zi-Han, FANG Yun-Ting
    Chin J Plant Ecol    2023, 47 (1): 114-122.   DOI: 10.17521/cjpe.2022.0085
    Accepted: 26 August 2022

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    Aims Nitrogen oxides (NOx = NO + NO2) are the world’s main atmospheric pollutants. Especially in China, NOx deposition has been increasing in recent years. When NOx enter the forest ecosystems accompanied by dry deposition, they reach the forest canopy first. Studies have shown that trees can assimilate NO2 deposited on leaf surfaces, but this process has been ignored in the forest N cycle models. Currently, the quantity of NO2 that can be assimilated by trees through foliage and the mechanisms of how the assimilated NO2 is distributed remain unclear.
    Methods In this study, we conducted a 15NO2 fumigation experiment with static chambers under dark and light conditions. We chose Schima superba and Pinus massoniana seedlings, the common tree species in southern China, as our experimental materials, and analyzed the whole 15N recovery and the distribution of assimilated 15NO2 in different tissues.
    Important findings The results show that trees assimilated NO2 mainly through stomata. Schima superba and P. massoniana could take up 10.3% ± 5.9% and 20.4% ± 7.0% 15NO2 in the whole plant under the dark condition, respectively; while 35.9% ± 5.4% and 68.2% ± 7.6% under light condition. The sequence of 15N recovery per dry mass in different tissues was leaves > branches > stem > roots. Most recovered NO2 remained in the leaves in a short period after fumigation. The 15N recovery in leaves of S. superba and P. massoniana accounted for 72% and 49% of the total recovery under the dark condition, and 91% and 96% under the light condition, respectively. This study indicates that the foliar assimilation of NO2 in forest ecosystems cannot be ignored. The process of foliar NO2 assimilation plays a key role in the N budget of forest ecosystems.

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    Applications of nitrogen stable isotope techniques in the study of nitrogen cycling in terrestrial ecosystems
    FANG Yun-Ting, LIU Dong-Wei, ZHU Fei-Fei, TU Ying, LI Shan-Long, HUANG Shao-Nan, QUAN Zhi, WANG Ang
    Chin J Plant Ecol    2020, 44 (4): 373-383.   DOI: 10.17521/cjpe.2019.0249
    Accepted: 26 March 2020

    Abstract2018)   HTML183)    PDF (1080KB)(3311)       Save

    In the past several decades, the development of nitrogen (N) stable isotope techniques has improved the understanding of N cycling in terrestrial ecosystems. This review briefly introduced the history of N stable isotope techniques in studying N cycling in terrestrial ecosystems and summarized typical studies focusing on different aspects of ecosystem N cycling in recent years, including using 1) 15N natural abundance to identify plant N sources, indicate N status of ecosystems, and quantify N transformation rates; 2) 15N enriched tracers to study N fates, redistribution and gaseous loss from ecosystems. In the end, this review points out challenges and future applications of N stable isotope techniques on studying N cycling in terrestrial ecosystems.

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    Cited: CSCD(11)
      
    Tracing technology of carbon isotope and its applications to studies of carbon cycling in terrestrial ecosystem
    GE Ti-Da, WANG Dong-Dong, ZHU Zhen-Ke, WEI Liang, WEI Xiao-Meng, WU Jin-Shui
    Chin J Plant Ecol    2020, 44 (4): 360-372.   DOI: 10.17521/cjpe.2019.0208
    Accepted: 03 January 2020

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    Recently developed in recent decades, the carbon isotope tracing technology is one of the most reliable methods, which has been widely used in the study of carbon (C) cycling in terrestrial ecosystems due to its high specificity and sensitivity. Here, the principle, analysis method and application process of C isotope tracing technology in C cycling in terrestrial ecosystem have been reviewed. Four different methods are currently being used in laboratory or field conditions, including natural abundance method, Free-Air Concentration Enrichment (FACE) technology coupling with 13C dilution method, pulse and continuous labeling with 13C enriched CO2, and labeling with 13C enriched substrates. Results of field experiments and lab incubation experiments employing carbon isotope tracing technology were combined in order to quantify the transformation and distribution of photosynthetic C in plant-soil system. Furthermore, these techniques also help to understand the contribution of plant photosynthetic C to soil organic matter, the stabilization of soil organic matter and its microbial mechanism, to illustrate the dynamic changes of soil organic carbon (SOC), evaluate the contribution of new and old organic C to soil C storage, and estimate the micromechanism of SOC input, conversion and the stabilization in terrestrial ecosystems. Carbon cycle is affected by climate, vegetation, human activities and other factors, and therefore it is imperative to further develop a sensitive, accurate, multiscale and multidirectional isotope tracing system by combining carbon isotopes with mass spectrometry, spectroscopy and molecular biological technology. We have summarized the coupled application of carbon isotope tracing technology and the insitu detection involving molecular and biological approaches, and discussed the existing issues of carbon isotope tracing technology.

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    Water isotope analysis for tracing ecosystem processes: measurement techniques, ecological applications, and future challenges
    TANG Xian-Hui, CHEN Yong-Le, LI Fang, SONG Xin
    Chin J Plant Ecol    2020, 44 (4): 350-359.   DOI: 10.17521/cjpe.2019.0204
    Accepted: 24 February 2020

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    Stable oxygen and hydrogen isotope analysis provides an important tool to trace, integrate or indicate water fluxes from leaf, whole-plant to ecosystem levels. Through measuring and analyzing the natural varitions in the hydrogen and oxygen isotope compositions of water from different components of ecosystem, we can partition evapotranspiration of ecosystem, determine source of plant water uptake, and study mechanism of leaf water isotope enrichment. As such, water isotope analysis has emerged as an indispensable technique to study the mechanism and ecological effects of different water cycle processes in ecosystem. In this paper, we briefly reviewed the history in development and application of water isotope analysis for terrestrial ecosystem studies, which then followed by more detailed introduction of the application principles and technical essentials. Furthermore, we reviewed progresses in diverse water-isotope based research field ranging from evapotranspiration partitioning, plant water uptake apportionment, sourcing of dew flux and precipitation vapor, to exploration leaf water isotope enrichment mechanisms and water-carbon coupling. Finally, we summarized technological and methodological challenges to be solved in the future ecological research, so as to fully realize the potential of water isotope analysis in various field of ecological research.

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    Applications and prospect of the flux-gradient method in measuring the greenhouse gases and isotope fluxes
    ZHAO Jia-Yu, XIAO Wei, ZHANG Mi, WANG Jing-Yuan, WEN Xue-Fa, LEE Xu-Hui
    Chin J Plant Ecol    2020, 44 (4): 305-317.   DOI: 10.17521/cjpe.2019.0227
    Accepted: 03 January 2020

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    Flux-gradient method and eddy covariance technique are classical micrometeorological methods, which observe fluxes of mass and energy. Flux-gradient method can effectively measure the greenhouse gas and isotope fluxes between ecosystem (or soil) and atmosphere although gas analyzer with high measuring frequency was not available or the fetch was small. Flux-gradient method can be viewed as an ancillary measurement and useful complement of eddy covariance technique. This paper reviewed from the following aspects: the fundamental theory, concepts and assumptions of flux-gradient method; the methods measuring the gradient of greenhouse gases and the theory on turbulent diffusion coefficients; the applications of this method in measuring greenhouse gas fluxes, especially on isotope fluxes, over various ecosystems including forest, cropland, grassland, wetland and water bodies. Finally, the considerations and suggestions were provided regarding the measurement on concentration gradients of greenhouse gases and isotopes, and the calculation of turbulent diffusion coefficients.

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    A review of the calibration methods for measuring the carbon and oxygen isotopes in CO2 based on isotope ratio infrared spectroscopy
    Jia-Ping PANG, Xue-Fa WEN
    Chin J Plant Ecol    2018, 42 (2): 143-152.   DOI: 10.17521/cjpe.2017.0206
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    With the development of isotope ratio infrared spectroscopy (IRIS) technology, it is now possible for the in situ high temporal resolution and high precision measurement of carbon isotopic composition (δ 13C) and oxygen isotopic composition (δ 18O) of atmospheric CO2, which overcomes the low temporal resolution and labor intensive shortcoming of traditional isotope ratio mass spectrometry (IRMS). The dependence of δ 13C and δ 18O on CO2 concentration (termed as concentration dependence) and the drift due to sensitivity to changing environmental conditions (termed as instrumental drift) are the two main sources of error affecting the IRIS measurements. Therefore, it is important to obtain precise measurements by constructing a proper calibration strategy to solve the concentration dependence and instrumental drift. In this study, we briefly discussed the definition and related theoretical principle of concentration dependence, and elaborated the theoretical and empirical calibration methods of concentration dependence. Moreover, we introduced the calibration methods of instrumental drift, and reviewed the state of the art of calibration methods and its application of IRIS technology. Additionally, we briefly discussed the definition and method of data traceability to the international standard, and reviewed its application of IRIS technology. Finally, we recommend that concentration dependence is corrected by using three standards or above with known CO2 concentration and its δ 13C and δ 18O, bracketing the CO2 concentration of samples. The instrumental drift is corrected by setting appropriate calibration frequency and all dataset are traceable to the international standard. In the future, the comparative study of different IRIS instruments and calibration methods should be enhanced, and the similar methods should be used for measuring CH4, N2O and H2O isotopes by IRIS technique. The IRIS technology combined with other technology will provide a new opportunity for ecological research.

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    Water-use process of two desert shrubs along a precipitation gradient in Horqin Sandy Land
    CHEN Ding-Shuai, DONG Zheng-Wu, GAO Lei, CHEN Xiao-Min, PENG Xin-Hua, SI Bing-Cheng, ZHAO Ying
    Chin J Plant Ecol    2017, 41 (12): 1262-1272.   DOI: 10.17521/cjpe.2017.0219
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    Aims The determination of the source of plant water is an important research on the plant-water relationship in arid and semiarid regions and helps to understand the adaptation strategy of desert species to the dry environment. Plant water use pattern affects plant community composition and ecosystem water budget. This study aims to investigate the water use patterns of Caragana microphylla and Artemisia halodendron, two typical shrub species, under altered rainfall conditions in Horqin Sandy Land. Methods Water treatments include ambient rainfall (natural rainfall), 50% increase in rainfall (enhanced rainfall) and 50% decrease in rainfall (reduced rainfall) by artificially intercepting and redistributing natural rainfall. Stable hydrogen and oxygen isotope ratios (δD and δ18O) were measured for xylem water, rainfall, and soil water in different soil layers (0-120 cm depth). The possible ranges of potential water sources used by C. microphylla and A. halodendron were calculated using the IsoSource model. Important findings 1) Alteration of ambient rainfall mainly affected the soil water condition in the shallow soil (0-30 cm). Increase in rainfall significantly increased the above- and below-ground biomass, and δ18O values of soil water declined with soil depth. 2) Under the enhanced rainfall treatment, A. halodendron mainly used the soil water in the shallow soil (0-40 cm) and C. microphylla was able to extract water from multiple soil layers. Under the reduced rainfall treatment, both species increasingly relied on extracting water from deeper soil layers, 60-80 cm for A. halodendron and 60-120 cm for C. microphylla. 3) For the natural rainfall treatment, in the wet season, the upper soil water was recharged by rainfall, C. microphylla and A. halodendron extract the shallow soil water (0-60 cm). However, in the dry season, soil water content was dramatically reduced, and main water sources for C. microphylla shifted from topsoil to deeper soil, and A. halodendron can use multiple layers of soil water. In summary, A. halodendron is more capable of exploring deeper soil moisture under reduced rainfall in comparison with C. microphylla, and is likely to be more adaptive to this water-limiting desert environment.
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    Differential uptakes of different forms of soil nitrogen among major tree species in subalpine coniferous forests of western Sichuan, China
    Ting-Ting ZOU, Zi-Liang ZHANG, Na LI, Yuan-Shuang YUAN, Dong-Hui ZHENG, Qin LIU, Hua-Jun YIN
    Chin J Plant Ecol    2017, 41 (10): 1051-1059.   DOI: 10.17521/cjpe.2017.0165
    Accepted: 19 December 2017

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    Aims Although acquisition of soil organic nitrogen (N)(mainly amino acids) by plants is a widespread ecological phenomenon in many terrestrial ecosystems, the rate of organic N uptake and their contributions to plant nutrient supply are poorly understood. Our objective was to determine the relative contributions of inorganic N (NO3-N and NH4+-N) and organic N (amino acids) to plant N uptake in a high-frigid forest ecosystem.Methods The differences in the uptake rate of three different forms of N (NO3-N, NH4+-N and glycine) were quantified by exposing seedlings of two dominant tree species (Picea asperata and Betula albo-sinensis) in subalpine coniferous forests of western Sichuan, China, to trace quantities of K15NO3,15NH4Cl and (U-13C2/15N) glycine.Important findings Both 13C and 15N were significantly enriched in fine roots 2 h after tracer application, indicating the occurrence of glycine uptake in P. asperata and B. albo-sinensis seedlings. The seedlings of two tree species had a significant preference for NO3-N compared with glycine and NH4+-N, and the uptake rate of NO3-N was 5 to 10 times greater than that of glycine and NH4+-N. The roots of seedlings in the two species took up glycine more rapidly than NH4+-N, implying that soil organic N (i.e., amino acids) could be an important N source for the two species in subalpine coniferous forests. The results of this study are of great theoretical significance for understanding N utilization strategies and nutrient regulation processes in plants of the high-frigid forest ecosystems.

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    Water sources of Populus euphratica and Tamarix ramosissima in Ejina Delta, the lower reaches of the Heihe River, China
    Ya-Fei LI, Jing-Jie YU, Kai LU, Ping WANG, Yi-Chi ZHANG, Chao-Yang DU
    Chin J Plant Ecol    2017, 41 (5): 519-528.   DOI: 10.17521/cjpe.2016.0381
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    Aims We aim to evaluate the water sources of typical riparian arbor species (Populus euphratica) and shrub species (Tamarix ramosissima), and analyze the spatial and temporal dynamics of plant water source in Ejina Delta, the lower reaches of the Heihe River, China.Methods Eight sampling sites were selected in the riparian zones along the East River and West River in Ejina. The plant xylem water, soil moisture, rainwater, stream water and groundwater were taken and pretreated during the growing season in 2015-2016, and the stable oxygen isotope ratio (δ18O) for each water sample was measured. The δ18O of plant xylem water and soil moisture were compared to estimate the dominant depth of root water uptake, and the linear-mixed model called “IsoSource” were applied to determine plant water sources and quantify their proportions.Important findings This study indicated that the main recharge sources for P. euphratica and T. ramosissima were stream water and groundwater. The contributions of rain water to them was negligible due to the limited amount and the shallow infiltration depth of local rainfall. As affected by groundwater level fluctuation, soil physical properties, as well as lateral and vertical recharge of stream water on soil moisture, the dominant depth of root water uptake spatially varied. However, the relative contributions of stream water or groundwater to plant water sources did not change significantly across space. Populus euphratica used more stream water (68%), while T. ramosissima used more groundwater (65%). Plant water sources were sensitive to environmental flow controls. The contributions of stream water to the water sources of the two species went up to 84% and 48% for P. euphratica and T. ramosissima respectively during the discharge period, but dropped to 63% and 30% during the non-discharge period. On the other hand, the contributions of groundwater decreased to 16% and 52% during the discharge period, but increased to 37% and 70% during non-discharge period. It is noteworthy that the high similarity of δ18O between stream water and groundwater due to extensive water exchange in the riparian zone made increase the uncertain in quantifying plant water sources.

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    Soil water use strategy of dominant species in typical natural and planted shrubs in loess hilly region
    Ting LÜ, Xi-Ning ZHAO, Xiao-Dong GAO, Yan-Hui PAN
    Chin J Plant Ecol    2017, 41 (2): 175-185.   DOI: 10.17521/cjpe.2016.0253
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    Aims Artemisia gmelinii is a dominant specie naturally established after abandonment of cultivated lands in the Loess Plateau, and Caragana korshinskii is one of the main planted shrub species to control soil erosion. Improved understanding of water use strategies of these two species is of great significance to evaluate the sustainable development of the Loess Plateau under the trend of climate warming and increasing drought events.
    Methods Stable oxygen-18 isotope was used to determine seasonal variations in the water sources of native A. gmelinii communities established after abandonment of cultivated lands for 7 and 30 years and planted C. korshinskii after 30 years. The contributions of soil water from different depths to water uptake were estimated by the MixSIR Bayesian mixing model. The geometric mean regression method was used to fit the line of precipitation to get the local meteoric water line (LWML).
    Important findings The stable hydrogen isotope rate (δD) and stable oxygen isotope rate (δ18O) of soil water and xylem water plotted to the right side of the LWML, indicating that the isotopic compositions of soil water were enriched due to evaporation. The native A. gmelinii communities established after abandonment of cultivated lands for 7 years and planted C. korshinskii after 30 years showed plasticity in switching water sources from different soil layers, extracting water from shallow soil (0-40 cm) when soil water was available, but deeper soil (40-80 cm) when shallow soil water was dry. In contrast, A. gmelinii growing in site after cultivation abandonment for 30 years mainly relied on water from the surface soil (0-10 cm) throughout the growing season. Our results suggest that the ability of A. gmelinii to compete for soil water reduces with aging of the community while the planted C. korshinskii will have competitive advantage under the condition of increasing frequency of drought events in the future.

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    Leaf water δD and δ18O enrichment process and influencing factors in spring maize (Zea mays) grown in the middle reaches of Heihe River Basin
    Xiao-Ting WANG, Xue-Fa WEN
    Chin J Plant Ecol    2016, 40 (9): 912-924.   DOI: 10.17521/cjpe.2015.0431
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    Aims The stable isotope fractionation of plant water is an important part for the water cycle in the soil-plant-atmosphere continuum. There is a lack of control mechanisms research of leaf water isotope ratio (δl,b) enrichment based on the field conditions. Because it is tough to get the measured 18O isotope ratio (δ18O l,b) and deuterium (D) isotope ratio (δDl,b) of leaf water (collective name δl,b). Therefore most previous research focuses on model building used the limited number of δl,b. Leaf water δDl,b and δ18O l,b enrichment (collective name Δl,b) is usually represented as the difference of the leaf water isotope ratio (δl,b) and the plant source water isotope ratio (δDx and δ18O x,collective name δx), that is Δl,b = δl,b - δx.
    Methods A field experiment with spring maize (Zea mays) was conducted in the middle reaches of Heihe River Basin to investigate the characteristics of leaf water δ18O and δD enrichment and their abiotic control mechanisms on seasonal and daily scales. Leaf and stem samples were collected and analyzed according to different time scales, and the δ18O and δD of atmospheric water vapor (collective name δv) were determined based on the in situ and continuous water vapor isotope ratio measurement system at the same time.
    Important findings The results showed that: δl,b and Δl,b of leaf water varied little during the experimental season while largely at daily scale, which enrichment was found at the daytime but depletion at night. Atmospheric water vapor isotope ratio (δv) and relative humidity were main factors to D on both seasonal and daily scales; for 18O, only relative humidity was the key control factor on both seasonal and daily scales. Differences of D and 18O came from the equilibrium fractionation because equilibrium fractionation factor for D was over 8 times than for 18O. The analysis of these differences help us distinguish the environmental factors of leaf water enrichment for D (ΔDl,b) from leaf water enrichment for 18O (Δ18Ol,b), and improve our understanding of leaf water enrichment process and develop the related models as well.

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    13C and 15N isotopic signatures of plant-soil continuum along a successional gradient in Dinghushan Biosphere Reserve
    Xin XIONG, Hui-Ling ZHANG, Jian-Ping WU, Guo-Wei CHU, Guo-Yi ZHOU, De-Qiang ZHANG
    Chin J Plant Ecol    2016, 40 (6): 533-542.   DOI: 10.17521/cjpe.2015.0478
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    Aims The optimal patterns of plant community for water use and nutrient utilization, the responses of soil carbon and nitrogen turnover processes to forest succession, and the mechanisms of soil organic carbon accumulation, are three critical issues in forest ecosystem study. It is difficult to accurately detect these ecological processes with conventional methodologies in the short term, yet the application of 13C and 15N natural abundance technique may yield important information about these processes.Methods This study was conducted in Dinghushan Biosphere Reserve. We investigated the natural isotopic abundance of both 13C and 15N of plant-soil continuum along a successional gradient from Pinus massoniana forest (PF) to coniferous and broad-leaved mixed forest (MF), and monsoon evergreen broad-leaved forest (BF). We also analyzed the correlations of foliar stable carbon isotope ratio (δ13C) and stable nitrogen isotope ratio (δ15N) with foliar elemental contents and the variations of soil δ13C and δ15N along soil profiles at different successional stages.Important findings A significant positive correlation between foliar δ13C and foliar C:N was observed. In both litter and soil, the δ13C values tended to decrease along the forest succession, with the order as PF > MF > BF. Foliar δ15N was positively correlated with foliar N content. The δ15N values of litter and upper soil (0-10 cm) increased with successional status. Both soil δ13C and δ15N values increased with increasing soil depth at all three forests. Our results imply that 1) trade-off between water use efficiency and nitrogen use efficiency did not necessarily exist in subtropical forests of China; 2) the application of isotopic technique could assist understanding of the mechanisms of soil carbon accumulation in subtropical forests, especially in old-grow forests; 3) the 15N natural abundance of plant-soil continuum could be a potential indicator of soil nitrogen availability and ecosystem nitrogen saturation status.

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    Interspecific water use strategies of a Juglans regia and Isatis tinctoria/Senna tora agroforestry
    Chun-Xia HE, Ping CHEN, Ping MENG, Jin-Song ZHANG, Hong-Guo YANG
    Chin J Plan Ecolo    2016, 40 (2): 151-164.   DOI: 10.17521/cjpe.2015.0360
    Abstract1670)   HTML4)    PDF (1221KB)(1446)       Save

    Aims Understanding the interspecific water relations is important for designing agroforestry systems. The objective of this study was to determine the water use strategies of component species in a walnut (Juglans regia)-woad (Isatis tinctoria)/sicklepod (Senna tora) agroforestry system.Methods Water sources of component species in a walnut-woad/sicklepod agroforestry system were investigated with the technique of stable deuterium isotope tracing at a site of hilly area in Northern China during 2012-2013.Important findings Results showed that the soil water content in the agroforestry system was 26.74% and 7.93% greater than in the pure woad field in the first half year, and 17.39% and 13.65% greater than in the pure sicklepod field in the second half year (sicklepod growth period), in 2012 and 2013, respectively. The lowest water content was found in the middle of tree rows, and the highest water content was found in the northern side of tree rows or under the trees. In the soil layers measured, the pure woad and pure sicklepod systems had greater hydrogen stable isotope ratios (&#x003b4 D value) of soil water than in the agroforestry system. During the period of woad growth, more than half of the water absorbed by walnut was from the deeper soil layer (30-80 cm). In contrast, the walnut trees mainly utilized shallow layer (0-30 cm) soil water during the period of sicklepod growth. These findings suggest that walnut has a two-state root system: during the period of woad growth, shallow roots of walnut are not active when soil is dry whereas the sicklepod growth occur in rainy season, and the shallow roots of walnut are active and utilize more shallow soil water supplemented by rainwater. More than 85% of water used by both the woad and the sicklepod were from the shallow layer soil. At the seedling stage, the roots of woad, cannot grow into the deeper soil layer, and the absorbed water is completely from the shallow layer in the pure woad system. However, 5.7% of the water absorbed by the intercropped woad was from the deeper soil layer in 2012, and the proportion increased further (9.7%) in the following year when there was less precipitation. The results confirmed that hydraulic lift effect of walnut occurred on shallow layer crop in dry season, and this effect become greater under drier conditions. Therefore, deeper roots of walnut improved water condition in the walnut- woad/sicklepod agroforestry systems compared to pure crop systems. The walnut mainly utilized water from the deeper layer to avoid water competition with the shallow layer. In the dry season, crops benefited from the water provided by walnut roots through hydraulic lift. Walnut and intercropped plants exhibited water facilitation in the agroforestry systems, suggesting that this configuration is a suitable practice in this area.

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    Foliar stable carbon isotope ratios of Phragmites australis and the relevant environmental factors in marsh wetlands in Tianjin
    CHEN Qing,WANG Yi-Dong,GUO Chang-Cheng,WANG Zhong-Liang
    Chin J Plan Ecolo    2015, 39 (11): 1044-1052.   DOI: 10.17521/cjpe.2015.0101
    Abstract1331)   HTML110)    PDF (370KB)(2032)       Save

    Aims Phragmites australis marshes in Tianjin play an important role in ecosystem functioning. Wetlands of Tianjin municipality have been suffering from serious nitrogen loading, salinization and water shortage. The foliar stable carbon isotope ratio (δ13C) is a good parameter which records environmental change information associated with the plant growth process, and reflects physiological and ecological responses of plants to environment changes. The objective of this study is to investigate the effects of environment stress on the leaf δ13C of P. australis in marsh wetlands in Tianjin municipality.Methods This study was conducted in Qilihai, Beidagang, and Dahuangpu marsh wetlands. We investigated the foliar δ13C of P. australis and sediment properties, and evaluated the relationships between the foliar δ13C and sediment environmental factors. Important findings 1) Foliar δ13C ranged from -26.3‰ to -23.6‰, with an average value of -25.8‰. 2) Sediment water and nitrogen status were the important factors affecting reed foliar δ13C. Foliar δ13C was negatively correlated to sediment relative water content, and positively correlated to sediment total nitrogen and available nitrogen content. In contrast, foliar δ13C was not significantly correlated to sediment salinity and phosphorus content. 3) Leaf δ13C were significantly positively correlated with leaf nitrogen content, and negatively correlated with leaf carbon and nitrogen ratio across all site. However, these relationships were not detected due to the wetland drainage at Qilihai site in August. Wetland drainage changed the plant water and nitrogen balance, and further affected water and nitrogen utilization strategies of P. australis. Moreover, wetland drainage had stronger effects on these processes than nitrogen loading and salinization.

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    Contribution of invasive species Spartina alterniflora to soil organic carbon pool in coastal wetland: Stable isotope approach
    WANG Dan,ZHANG Rong,XIONG Jun,GUO Hai-Qiang,ZHAO Bin
    Chin J Plan Ecolo    2015, 39 (10): 941-949.   DOI: 10.17521/cjpe.2015.0091
    Abstract1599)   HTML31)    PDF (504KB)(2616)       Save
    <i>Aims</i>

    Spartina alterniflora was introduced into China because of its strong sedimentation promotion ability, currently, it became one of the most invasive species along coastal areas. Most researches focused on its high productivity which directly increased soil carbon (C) input. However, little is known about its indirect contribution to soil carbon via increased sedimentation.

    <i>Methods</i>

    Spartina alterniflora patches with different invasion history (4, 6, and 10 years) was selected in Chongming Dongtan wetland, and Phragmites australis and mudflat were chosen as control respectively. The plant, soil and water samples were collected for C and nitrogen (N) analysis. Based on the stable isotope ratio of C and N in plant and soil organic carbon, the contribution of soil organic carbon pool from S. alterniflora patches were estimated by using 2 and 3 sources mixing model, respectively.

    <i>Important findings</i>

    (1) The soil organic C content and stable carbon isotope ratio of S. alterniflora patches increased with time. Spartina alterniflora invasion cumulatively enhanced soil organic carbon pool. The soil C:N ratio decreased with invasion history and became close to the redfield ratio, indicating the important role of sedimentation input. (2) The contribution of invasive S. alterniflora to soil organic carbon pool increased with time, but the sedimentation contribution dropped gradually. In patch with 4 years invasion history, the contribution ratio of sedimentation was more than 90.0%. While in patch invaded 10 years ago, the sedimentation contribution reduced by 18.4%, and in comparison, S. alterniflora contributed up to 73.5% to soil organic carbon pool. These findings suggested that S. alterniflora contributed to soil organic carbon pool mainly by promoting sedimentation in early invasion period, while gradually relied on its own productivity with invasion time.

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    Cited: CSCD(13)
      
    A review of research on responses of leaf traits to climate change
    WANG Chang-Shun,WANG Shi-Ping
    Chin J Plan Ecolo    2015, 39 (2): 206-216.   DOI: 10.17521/cjpe.2015.0020
    Abstract1997)   HTML72)    PDF (370KB)(3511)       Save

    Leaf traits reflect the highly adaptable and self-regulatory capacity of plants to complex environmental conditions. That how they respond to climate change is one of key topics in studies of plant adaptability. This review synthesizes the current understanding on the responses of leaf size, specific leaf mass, leaf nitrogen content and carbon isotopes to climate change. The responses of leaf traits to climate change vary with different leaf structures and ecological properties. Thus, a single leaf trait cannot be used to fully reflect the responses of plants to climate change. There are still a lot of uncertainties concerning the effects of climate change on leaf traits under different scales. Studies are relatively lacking in the alpine region. This review helps us to better understand the relationships between leaf traits and climate as well as the responses and adaptation of plants to climate change. It is critical to predict the variations and evolutionary strategies of plants in response to future climate change.

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    Cited: CSCD(72)
      
    Application of stable hydrogen isotope in study of water sources for Caragana microphylla bushland in Nei Mongol
    ZHENG Xiao-Ran,ZHAO Guo-Qin,LI Xiao-Yan,LI Liu,WU Hua-Wu,ZHANG Si-Yi,ZHANG Zhi-Hua
    Chin J Plan Ecolo    2015, 39 (2): 184-196.   DOI: 10.17521/cjpe.2015.0018
    Abstract1200)   HTML91)    PDF (744KB)(1459)       Save
    <i>Aims</i>

    Caragana microphylla is a dominant shrub widely distributed in the grasslands of Nei Mongol. Its water utilization pattern has an important effect on local plant community composition. However, the water source for C. microphylla remains poorly quantified, which is vital in understanding the adaptation of this specie to arid environment. This study aims to investigate the dynamics of water use in C. microphylla and its response to soil water fluctuations resulting from precipitation pattern including summer rains and winter snow.

    <i>Methods</i>

    Seasonal variations of hydrogen stable isotope ratios (δD) in the xylem of C. microphylla and potential sources of water (summer rains, winter snow and soil water) were analyzed by LGR hydrogen stable isotope tracer method. The contribution of soil water to C. microphylla was calculated by IsoSource model and the contribution of rainfall to soil water was calculated by a two-source model.

    <i>Important findings</i>

    The xylem of C. microphylla (xylem) showed no seasonal differences in δD, whereas there were significant differences in the water source of plants between two contrasting hydrological environments. In habitats where rainfall was shielded off, C. microphylla mainly used the soil water at depth of 0-20 cm, which accounted for 73.30% ± 16.14% of the total water usage; whilst under natural conditions, water uptake by C. microphylla was more or less similar at the depths of 0-20 cm, 20-60 cm and 60-100 cm, accounting for 34.66% ± 7.83%, 32.44% ± 7.42%, 32.90% ± 4.14% of the total water usage, respectively. Competition for water between shrubs and grasses gave a possible explanation for different water utilization patterns of the plants. In addition, rainfall accounted for 42.65%-63.92% of the water sources for C. microphylla. Resultsin this study demonstrated that C. microphylla used both summer rains and winter snow, and dynamics of water use in C. microphylla reflects its adaptation to the water-limiting arid environment.

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    Water sources of Medicago sativa grown in different slope positions in Yanchi County of Ningxia
    ZHU Lin,QI Ya-Shu,XU Xing
    Chin J Plant Ecol    2014, 38 (11): 1226-1240.   DOI: 10.3724/SP.J.1258.2014.00118
    Abstract1163)   HTML33)    PDF (1056KB)(1553)       Save
    Aims Alfalfa (Medicago sativa) is considered as an elite forage with high economic and ecological values. In semi-arid areas of Northwest China, the low rainfall is far from satisfying water demand of alfalfa. The northern part of Yanchi County is adjacent to Mu Us desert and has a shallow groundwater table. In this area, groundwater could be the potential water sources for growing alfalfa. Our objective was to investigate the growth performance and potential water sources of alfalfa grown in four slope positions with different altitudes in the bottomland of northern Yanchi County. Method Stable 18O and D isotope compositions (δ 18O and δD) of different water sources and xylem water were analyzed in April, June, July and August 2013. IsoSource was used to calculate the probable contribution of different water sources to the total plant water uptake. Stomatal conductance, carbon isotope discrimination (Δ 13C) of whole plant, soil volumetric water content in the 0-300 cm soil profile were also determined. Important findings Slope position had a significant effect on water content in the 0-300 cm soil profile. Highest soil water content was found in the slope position of lowest altitude. The δ 18O-δD coordinates of soil water and plant stem xylem water were distributed on the right of Northwest China local meteoric water line (LMWL), indicating that oxygen and hydrogen isotopic compositions in the water sources of alfalfa were subjected to enrichment due to evaporation. The δ 18O values of soil water in the 0-450 cm profile increased with altitude. Soil water δ 18O values decreased with the depth of soil profile for a given slope position. Soil water δ 18O values in deep profile were similar to those in groundwater, implying that groundwater would move to the upper soil layer via soil capillary. Seasonal fluctuation was observed in soil water δ 18O in the 0-40 cm profile, while soil water δ 18O in profile below 270 cm was stable seasonally. Plant stem xylem water δ 18O value was significantly lower (p < 0.001) in the slope position 1 than in other three slope positions in April, July and August. Highest water utilization rate from deep soil profile (below 270 cm) was recorded for alfalfa grown in the slope position 1 in April, June and July. In August, alfalfa grown in the slope positions 1, 3 and 4 mainly used soil water in the 150-270 cm and 270-450 cm profiles and groundwater; highest dependence on soil water in the shallow profile (0-20 cm) was found in alfalfa grown in the slope position 2. Higher yield, whole plant Δ 13C value and stomatal conductance were observed in alfalfa grown in the slope position 1 than in other three slope positions. These results suggest that bottomland with lower altitude and shallow groundwater table should be adopted when planting alfalfa without irrigation in the semi-arid areas of Northwest China where average annual rainfall is around 280 mm. Thus, groundwater could contribute to better growth performance of alfalfa, leading to higher ecological and economic returns.
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    Dynamics of water usage in Haloxylon ammodendron in the southern edge of the Gurbantünggüt Desert
    DAI Yue,ZHENG Xin-Jun,TANG Li-Song,LI Yan
    Chin J Plant Ecol    2014, 38 (11): 1214-1225.   DOI: 10.3724/SP.J.1258.2014.00117
    Abstract915)   HTML9)    PDF (982KB)(1740)       Save
    Aims Plant water use is an important aspect of plant-water relations in desert regions, and is vital in understanding the adaptation of desert species to arid environment. Haloxylon ammodendron is a dominant plant species in the Gurbantünggüt Desert, China. Its water use pattern has an important effect on water balance of the local ecosystem and plant community composition. This study aims to investigate the dynamics of water usage in H. ammodendron and its response to soil water fluctuations resulting from precipitation pulses.Methods Oxygen stable isotope ratios (δ 18O) were measured for xylem water, soil water in different soil layers (0-300 cm depth), precipitation and groundwater. Four potential water sources were classified: shallow (0-40 cm), middle (40-100 cm) and deep soil water (100-300 cm), and groundwater. The possible ranges of potential water sources used by H. ammodendron were calculated using the IsoSource model. Important findings Main water sources for H. ammodendron shifted from the shallow soil water in April to the groundwater during May to September. In April, the contributions of shallow soil water were in the range of 62%-95%, and the possible ranges of middle and deep soil water and groundwater were 0-8%, 0-15% and 0-38%, respectively. However, during May to September, the contribution of shallow soil water decreased drastically while that of groundwater increased rapidly. Contributions of groundwater were in the range of 68%-100%. Haloxylon ammodendron responded differently to two similar precipitation pulses occurred in different months. After the 6.7 mm precipitation pulse on May 22, the usage of soil water increased from 9.8% prior to the event to maximum at 40.4% one day after rainfall (May 23), while the usage of groundwater decreased from 83%-98% to 42%-81%. After 7 mm precipitation pulse on August 31, the usage of soil water was almost unchanged and the usage of groundwater was still up to 71%-98%, implying that roots of H. ammodendron in the upper soil layer are inactive due to the long-lasting low soil water content. Hence, H. ammodendron seemed to be insensitive to the August precipitation pulse. The shallow soil water recharged by snowmelt and precipitation in spring and groundwater are two important water sources for H. ammodendron. Dynamics of water usage in H. ammodendron reflects its adaptation to this water-limiting desert environment.
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    Ecological implications of hydraulic redistribution in nutrient cycling of soil-plant system
    SU Hua,LIU Wei,LI Yong-Geng
    Chin J Plant Ecol    2014, 38 (9): 1019-1028.   DOI: 10.3724/SP.J.1258.2014.00096
    Abstract1294)   HTML70)    PDF (97512KB)(1558)       Save

    Hydraulic redistribution (HR), one of the common bio-physical processes, plays key roles in mediating plant drought stress, regulating plant interspecific relations and community composition, as well as in influencing water and carbon balance of ecosystems. Great improvements have been achieved in HR research with fast development of isotopic labelling and tracing technologies. This paper summarizes the effects of HR on nutrient cycling of soil-plant system, based on studies over the past decade. HR increases soil water content in dry soil layers, thus helping to prevent embolism in roots, increasing the survival rate and the growth rate of fine roots and improving microbial activities. Such effects improve plant nutrient uptake, i.e., hydraulic lift promotes nitrogen uptake from upper soil layers and hydraulic descent promotes phosphorus uptake from deep soil layers. HR may facilitate nutrient exchange between upper and lower soil nutrient pools, improve nutrient flows and regulate the N:P ratio in both plants and soil. These effects may ultimately affect global ecosystems. Under the global change scenarios (e.g. nitrogen deposition), it is necessary to further explore the effects of HR on biogeochemical cycles. HR should be taken into account when using ecosystem models for future predictions.

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    Morphological traits and physiological characteristics in drought tolerance in 20 shrub species on the Qinghai-Xizang Plateau
    QIU Quan,PAN Xin,LI Ji-Yue,WANG Jun-Hui,MA Jian-Wei,DU Kun
    Chin J Plant Ecol    2014, 38 (6): 562-575.   DOI: 10.3724/SP.J.1258.2014.00052
    Abstract1886)   HTML116)    PDF (13513KB)(2067)       Save

    Aims Providing indispensably theoretical evidence for establishing indices of evaluation on drought tolerance in shrubs, and screening for tree species that are drought tolerant for afforestation in arid regions or for matching their characteristics with suitable habitat conditions are the key to vegetation restoration in the Qinghai-Xizang Plateau. However, these issues are not adequately addressed in recent research due to lack of systematic methods. Therefore, our objective was to make a comprehensive evaluation on drought tolerance in 20 shrub species collected from different areas in Qinghai-Xizang Plateau, and to study their underlying mechanisms in drought tolerance.
    Methods We made measurements on variables depicting root characteristics, including the root length (TRL), surface area (TRSA), volume (TRV), and tips number (TRTN) of all roots, the root length (FRL), surface area (FRSA), volume (FRV), and tips number (FRTN) of fine roots (d≤2 mm), and derived plant characteristic indices including thickness of cuticle (CT), thickness of palisade tissue (TPT), thickness of spongy tissue (TST), TPT/TST, thickness of leaf (LT), palisable tissue cell density, and tissue structural tense ratio (CTR = TPT/LT × 100%) and spongy tissue loosened ratio (SR = TST/LT × 100%) of leaf anatomical structure, root to shoot ratio (RSR), leaf transpiration rate (Tr), instantaneous water use efficiency (WUEi), and carbon isotopic composition (δ13C) of the 20 shrub species through field experiments. Correlation analysis and principal component analysis were performed on the 19 variables and indices.
    Important findings Different shrubs had different mechanisms of drought tolerance. In this study, the character- istics of drought tolerance were mainly categorized into 6 types, involving modifications of (1) root systems, (2) leaf anatomical structure, (3) leaf pattern, and (4) biomass allocation, or via (5) low water-consumption and (6) high WUEi. Different genera or different tree species within the same genus clearly differed in drought tolerance. The species of the genus Hippophae were relatively poorly tolerant to drought, whereas several shrubs including Potentilla fruticosa, Berberis julianae, Caragana arborescens, Spiraea salicifolia and Hippophae rhamnoides ssp. mongolica occurred to be more drought tolerant than other shrub species investigated in this study. On the other hand, there were highly significant correlations among the characteristics of root systems and among characteristics of leaf anatomical structure. The results of principal component analysis on 19 variables and indices showed that TRL, TRSA, TRV, TRTN, FRL, FRSA, FRV, FRTN, CT, TPT, TST and WUEi could be effective indicators of drought tolerance of shrubs in the Qinghai-Xizang Plateau. In addition, the drought tolerance of shrubs had a close connection with their origin of collections; the shrubs collected from Xining prefecture in Qinghai Province were more drought tolerant than those from Tianshui Prefecture in Gansu and Lasa Prefecture in Xizang.

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    Nitrogen uptake and allocation characteristics of alpine meadow main species under water and nitrogen additions based on 15N isotope
    DENG Jian-Ming, YAO Bu-Qing, ZHOU Hua-Kun, ZHAO Xin-Quan, WEI Qing, CHEN Zhe, WANG Wen-Ying
    Chin J Plant Ecol    2014, 38 (2): 116-124.   DOI: 10.3724/SP.J.1258.2013.00038
    Abstract1334)   HTML91)    PDF (2202KB)(1908)       Save

    Aims Resource-use differentiation among species, which can reduce species competition for the same resources, is the main mechanism to maintain species diversity. Changes in soil temperature and moisture conditions, in the context of global change, may affect nitrogen (N) nutrition of plants of alpine meadow ecosystems. Our objective is to compare the characteristics of N uptake and resource allocation of dominant species of alpine meadow with changes in soil N and water.
    Methods An alpine meadow was treated with N and water addition for three years using the method of 15N isotope injection. We determined the growth responses of dominant species to the N and water additions, as well as the features of N uptake capacity, N allocation and root to shoot ratio.
    Important findings The species showed significantly different responses to the N and water treatments, with respect to functional traits of species in N absorption capacity, root N content and root to shoot ratio. There was no significant relationship between N absorption capacity and root N content, whereas N absorption capacity was negatively correlated with root to shoot ratio across all plant species. These results indicated there was ecological niche differentiation in N uptake and a trade-off between the N absorption capacity and resource allocation strategies among species.

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    Study on plant water use in Myricaria squamosa with stable hydrogen isotope tracer in Qinghai Lake basin
    ZHAO Guo-Qin, LI Xiao-Yan, WU Hua-Wu, ZHANG Si-Yi, LI Guang-Yong
    Chin J Plant Ecol    2013, 37 (12): 1091-1100.   DOI: 10.3724/SP.J.1258.2013.00112
    Abstract1014)   HTML5)    PDF (115241KB)(1519)       Save

    Aims Little study has been conducted to quantify plant water sources for Myricaria squamosa, which is a dominant alpine riparian shrub in the Qinghai Lake basin and plays a key role in maintaining riverine wetland system. The objective of this study was to quantify water sources for M. squamosa growing under different hydrological conditions.
    Methods We collected the water samples from the xylem of M. squamosa, groundwater, river, and soils in the Qinghai Lake basin from June through September, and analyzed the seasonal variation of hydrogen stable isotope ratio (δD) in the xylem and potential water sources using stable hydrogen isotope tracer method. We then compared the differences in water sources for M. squamosa growing under two contrasting hydrological conditions.
    Important findings Myricaria squamosa plants growing on the river bank mainly used groundwater and water from the river stream in June and July, with groundwater contributing up to 89% of water use in June and 55% in July and river stream contributing up to 86% in June and 65% in July, respectively; whilst in August, they used water mainly from the 0-20 cm soil layer; the water source in September was identifiable. In contrast, Myricaria squamosa plants growing approximately about 100 m away from the river bank mainly accessed the groundwater and river water in June (91% and 70%, respectively), and used water from the 0-60 cm soil layer during the rainy months July, August and September. Results suggest that M. squamosa plants on the river bank use mainly groundwater and river water; soil water was more important for those far away from the river bank. These are resulted from the responses of this shrub species to specific water conditions when growing under contrasting water regimes.

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    Differences and similarities between water sources of Tamarix ramosissima, Nitraria sibirica and Reaumuria soongorica in the southeastern Junggar Basin
    ZHOU Hai,ZHENG Xin-Jun,TANG Li-Song,LI Yan
    Chin J Plant Ecol    2013, 37 (7): 665-673.   DOI: 10.3724/SP.J.1258.2013.00069
    Abstract1327)   HTML3)    PDF (7346KB)(1648)       Save

    Aims Water is the most important limiting factor for plant growth in desert ecosystems. Our objective was to investigate the water sources of three co-existing desert plants and illustrate seasonal variation characteristics in southeastern Junggar Desert in China.
    Methods We investigated three kinds of desert plants (Tamarix ramosissima, Nitraria sibirica and Reaumuria soongorica) in the same habitat and measured hydrogen and oxygen stable isotope ratio (δD and δ18O) values of their xylem water and potential water sources (precipitation, soil moisture and ground water). The IsoSource model was then used to calculate probable contributions of potential water sources to total plant water uptake.
    Important findings The water sources of the three desert plants had obvious seasonal characteristics. Reaumuria soongorica and N. tangutorum obtained a high proportion of water from shallow soil water (0-100 cm) in spring. However, during the summer and autumn, R. soongorica tended to use deeper soil water, and N. tangutorum tended to use ground water. Tamarix ramosissima obtained 90% of its water from deep soil water and ground water, and there were no seasonal variations. The three kinds of plants had different water sources closely related to their water use strategies. This shows desert shrubs, through self-regulation, could tend to their optimal phenotypes and maximize water uptake.

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    Response of Rumex dentatus foliar nitrogen and its allocation to altitudinal gradients along Balang Mountain, Sichuan, China
    FENG Qiu-Hong,CHENG Rui-Mei,SHI Zuo-Min,LIU Shi-Rong,WANG Wei-Xia,LIU Xing-Liang,HE Fei
    Chin J Plant Ecol    2013, 37 (7): 591-600.   DOI: 10.3724/SP.J.1258.2013.00061
    Abstract1177)   HTML5)    PDF (7576KB)(1671)       Save

    Aims As a key element in plant tissue, nitrogen plays an important role in the growth and development of plants. Our objective is to determine (1) how both leaf nitrogen and its allocation between photosynthetic and non-photosynthetic systems have responded to an altitudinal gradient and (2) what role their response has played in the adaptation of Rumex dentatus to its changed environment along the altitudinal gradient.
    Methods We measured foliar parameters of photosynthesis, diffusional conductance to CO2, stable carbon isotope ratio (δ13C), nitrogen content and specific leaf area (SLA) of the forb R. dentatus in four sites with different altitudes (2350, 2700, 3150 and 3530 m) in the Wolong Reserve. One-way ANOVA was used to find the differences for all parameters among R. dentatus plants from different altitudes, and standardized major axis (SMA) was used to determine the relationships among some main parameters.
    Important findings Leaf nitrogen content per area (Narea) increased as maximum photosynthetic capacity (Amax) increased with altitude in R. dentatus. Increased diffusional conductance also had a positive effect on increased photosynthetic capacity with altitude. These may be the result of adaptation of plants to a shortened leaf lifespan caused by low temperature at high altitude. Along with the altitudinal gradient, nitrogen and diffusional conductance of R. dentatus have an indirect effect on foliar δ13C through acting on the ratio of chloroplast partial pressure of CO2 to ambient CO2 partial pressure (Pc/Pa). Compared with diffusional conductance, nitrogen (or carboxylation capacity based on nitrogen) played a more important role in the process, in order to increase foliar δ13C with altitude. Rumex dentatus allocated more nitrogen to build defensive structural tissue with increased altitude. This is why SLA and photosynthetic nitrogen use efficiency (PNUE) decreased with altitude. In the photosynthetic system, more nitrogen was allocated to light-harvesting components in order that enhanced light resource was used preferably by R. dentatus, and then photosynthetic capacity was increased with altitude. Nitrogen and its allocation among systems (especially between photosynthetic and non-photosynthetic systems) are the keys to the adaptation and the response of R. dentatus to the gradient in altitude.

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    Intra-annual variation in δ 13C from tree rings of Pinus sylvestris var. mongolica and its response to climatic factors
    SHANG Zhi-Yuan, WANG Jian, CUI Ming-Xing, CHEN Zhen-Ju
    Chin J Plant Ecol    2012, 36 (12): 1256-1267.   DOI: 10.3724/SP.J.1258.2012.01256
    Abstract1280)   HTML7)    PDF (566KB)(2640)       Save

    Aims We assess the relationship among the carbon isotopic signatures of earlywood (EW), transitional wood (TW) and latewood (LW) from tree rings. Our aims were to investigate variation in the intra-annual stable carbon isotope ratio (δ 13C) in Pinus sylvestris var. mongolica and determine the relationship between them and homologous ring width. Methods Based on two tree discs of Pinus sylvestris var. mongolica sampled from the northern part of Daxing’an Mountains in China, the EW, TW and LW were obtained with different stripping and pooling programs. After performing ring widths measurement and cross-dating, the periods analyzed were the maximum growth periods for one sample and different growth periods for the other. The holocellulose fractions were extracted and the intra-annual δ 13C of samples were measured. Important findings In general, the δ 13C values of TW are the highest, EW come second and LW are the lowest. The intra-annual trend of δ 13C is fluctuateing prominently from the juvenile period to the fast-growing period and is smoother from the maturation period to the senescence period. The variation amplitude of LW is almost greater than EW at the same period. The δ 13C of LW is always prominently higher than EW for the juvenile period. The difference between EW and LW is indistinctive for the maturation period and is negligible for the senescence period. The intra-annual variability of δ 13C concentrates on the middle and later phase of the growing season. The correlation relationship between the intra-annual δ 13C sequences and homologous detrended ring width sequences (dRWS) decreases with the seasons, which implies that environmental factors play a dominant role in cell formation and carbon fractionation during the middle and later phase of the growing season in each year. The ring width of EW of the current year is positively correlated with LW of the previous year (pLW). Also the δ 13C of EW is negative correlated with the incorporative dRWS of EW + pLW. But the correlation between δ 13C of EW and δ 13C or dRWS of pLW is statistically insignificant. The growing season could be divided as: EW (from late April to middle June, with greater soil moisture and rapidly increasing temperature), TW (from late June to middle July, with lower soil moisture and maximum temperature) and LW (from late July to middle September, with greater soil moisture and decreased temperature).

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    New advances in seed geography
    YU Shun-Li, FANG Wei-Wei
    Chin J Plant Ecol    2012, 36 (8): 918-922.   DOI: 10.3724/SP.J.1258.2012.00918
    Abstract1373)   HTML3)    PDF (287KB)(2551)       Save

    We add research content and several hypotheses and also amend some scientific questions in the field of seed geography. Three research areas that we expound upon are the geographies of soil seed banks, seed rain and seed dispersal syndromes. We summarize two hypotheses: 3-dimensional (latitude, longitude and altitude) variation hypotheses on soil seed banks and on seed dispersion modes. We also supplement the geography of seed chemical elements with seed isotope content. In the geography of seed mass, we mention elaiosomes. In the geography of seed morphology, we reaffirm use of length and width of seed and their ratio, absence or presence of seed (or fruit) wings, length and width of seed wings and their ratio, etc. In the geography of fruits and flowers, we add length and width of flower sepal and petal, as well as length, width and height of fruits and also percentage of fruit ripe in summer and autumn. In the geography of seed genetic characteristics, we add seed DNA content. In the geography of seed cell characteristics, we include seed starch grain. Overall, seed geography is a constantly developing field that should incorporate additional research from seed science and technology.

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    Cited: CSCD(11)
      
    Water sources of shrubs grown in the northern Ningxia Plain of China characterized by shallow groundwater table
    ZHU Lin, XU Xing, MAO Gui-Lian
    Chin J Plant Ecol    2012, 36 (7): 618-628.   DOI: 10.3724/SP.J.1258.2012.00618
    Abstract1851)   HTML3)    PDF (545KB)(1962)       Save

    Aims Shallow groundwater table is the main cause of salinization in the northern Ningxia Plain of China. The uptake of groundwater by halophytes can lower the groundwater table and reduce the demand for irrigation. Our objective was to investigate the potential water sources (different soil profile and groundwater) of four shrubs, i.e., twenty-year-old Tamarix ramosissima and three-year-old T. ramosissima, Lycium barbarum and Atriplex canescens.

    Method Stable18O and D isotope compositions (δ18O and δD) of different potential water sources and xylem water were analyzed before and after irrigation. The IsoSource mode was used to calculate the probable contribution of different water sources to the total plant water uptake. The photosynthetic gas exchange parameters, contents of salt and water and pH in 0-200 cm soil profile were also determined.

    Important findings Soil water δ 18O and δD in different depths differed consistently. The soil water δ 18O and δD values decreased with depth. More negative soil water δ 18O and δD values were recorded after irrigation. There were significant effects of evaporation and irrigation on soil water δ 18O and δD values. δ 18O and δD values of twenty-year-old T. ramosissima were lower than that of the three-year-old shrubs. Before irrigation, the three-year-old T. ramosissima, L. barbarum and A. canescens mainly tapped water in the upper soil layer (70.1%, 52.3% and 48.9%); highest groundwater uptake rate (21.5%) was observed for twenty-year-old T. ramosissima. After irrigation, higher water uptake rates from 80-140 cm soil profile were recorded for three-year-old T. ramosissima (59.5%) and L. barbarum (58.8%). Highest groundwater uptake rate was found for twenty-year-old T. ramosissima (18.3%). Before irrigation, the net photosynthetic rate, stomatal conductance and transpiration rate of twenty-year-old T. ramosissima were higher than those of other shrubs. Highest net photosynthetic rate were observed for three-year-old A. canescens after irrigation. Irrigation had significant effects on net photosynthetic rate and stomatal conductance of three-year-old T. ramosissima and L. barbarum. The intrinsic water use efficiency of three-year-old A. canescens was higher than other shrubs. These results suggested that different shrubs have different water use strategies, which is presumably related to species and age of shrubs. Young T. ramosissima mainly extracted soil water from upper un-saturated profile based on its strong tolerance to drought, and it switched its water use to middle soil profile after irrigation. Mature T. ramosissima turned out to bephreatophytic with growth being heavily dependent on groundwater and deep soil water and unresponsive to irrigation.

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    Cited: CSCD(13)
      
    Diurnal variations of soil evaporation δ18O and factors affecting it in cropland in North China
    YANG Bin, XIE Fu-Ti, WEN Xue-Fa, SUN Xiao-Min, WANG Jian-Lin
    Chin J Plant Ecol    2012, 36 (6): 539-549.   DOI: 10.3724/SP.J.1258.2012.00539
    Abstract1700)   HTML6)    PDF (584KB)(1613)       Save

    Aims The δ18O of soil evaporation (δE) is an important factor controlling the variations of atmospheric δ18O (δv), and it is also one of the key challenges of partitioning evapotranspiration into evaporation and transpiration components. δE is mostly simulated by the Craig-Gordon model, which is constrained by the δv of water vapor, the relative humidity (h), the equilibrium and kinetic factors and the δ18O of soil water (δs) at the evaporating front. Our objective is to investigate the diurnal variations of δE and factors affecting it.
    Methods We determined the δ18O of water vapor in a winter wheat-summer maize cropland based on the in-situ and continuous water vapor isotope ratio measurement system. We sampled soil water at different depths and analyzed it using the cryogenic vacuum distillation technique to acquire the δ18O of soil water at the evaporating front.
    Important findings During the growing period of winter wheat-summer maize, the diurnal variation of δE exhibited a bimodal pattern with peaks at 6:00 and 15:00. The h has a significant effect on the diurnal variation of δE in cropland ecosystems, and causes the Craig-Gordon model to be invalid under high humidity condition of h > 95%. The in-situ and high resolution measurement of δv overcomes the uncertainty of using the local precipitation equilibrium method to evaluate δv, which improves the accuracy of δE. Different equilibrium factors have no significant influence on the accuracy of δE. Different kinetic factors, especially the canopy scale kinetic factor, influence the accuracy of δE significantly. The location of the evaporating front determines the h normalized to soil temperature and the δ18O of soil water directly and also influences the accuracy of δE significantly. Further research is needed to attain direct measurement of δE by combining isotope ratio infrared spectroscopy (IRIS) with the static chamber or dynamic chamber.

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    Cited: CSCD(5)
      
    Use of 15N natural abundance in nitrogen cycling of terrestrial ecosystems
    YAO Fan-Yun,ZHU Biao,DU En-Zai
    Chin J Plant Ecol    2012, 36 (4): 346-352.   DOI: 10.3724/SP.J.1258.2012.00346
    Abstract2417)   HTML30)    PDF (17218KB)(3406)       Save

    Stable isotope technique has been widely used in ecology research with the increasing concern on global change. Our objectives are to better understand the impacts of nitrogen addition and other environment changes on the nitrogen cycling of terrestrial ecosystem, predict the consequent changes in environmental conditions, and provide a reference for policy making to help ensure the sustainable development of terrestrial ecosystems. Based on the relationship between nitrogen (N) isotope composition (δ 15N) in ecosystem N status and soil N cycle, we summarized the effects and mechanisms of N input and other environment changes on δ 15N of plant and soil. Most studies show significant positive relationships between N input and δ 15N values of plant and soil. Higher N input increases soil N availability, which leads to 15N enrichment in soil because of mass discrimination during soil N cycling processes. Foliar δ 15N also will be higher as plants take up the relatively 15N-enriched soil available N. 15N natural abundance can be a useful tool for assessing nitrogen saturation and N cycling.

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    Cited: CSCD(17)
      
    Effects of different ratios of straw to N-fertilizer on growth of Malus hupehensis seedling and its absorption, distribution and utilization of nitrogen
    CUI Tong-Li, JIANG Yuan-Mao, PENG Fu-Tian, WEI Shao-Chong
    Chin J Plant Ecol    2012, 36 (2): 169-176.   DOI: 10.3724/SP.J.1258.2012.00169
    Abstract1720)   HTML6)    PDF (368KB)(1759)       Save

    Aims The study was to explore the effects of different ratios of straw to N-fertilizer on growth of Malus hupehensis seedlings and 15N absorption, distribution and utilization in them.
    Methods Using 15N trace technique, we measured growth parameters (plant height, basal stem diameter and dry weight) and 15N parameters (absorption, N derived from fertilizer, distribution and utilization) of two-year-old M. hupehensis seedlings and C/N ratio in soil organic matter under different straw-nitrogen fertilizer treatments.
    Important findings Seedlings grew best under the condition of 45 : 1 of soil to straw and 300 mg·kg-1 N addition, showing the greatest height, basal stem diameter and total dry weight: 85.33 cm, 8.05 mm and 74.68 g, respectively. Total nitrogen, the 15N uptake and 15N utilization were also greatest: 0.938 g, 29.2 mg and 9.7%, respectively. The root/shoot ratio of seedlings without addition of straw (the control treatment) was 1.54, higher than those of other treatments. The 15N derived from fertilizer (Ndff) values of the aboveground parts for all the treatments were higher than those of the belowground parts, and the control showed the highest Ndff values in both aboveground and belowground parts, which were 7.94% and 4.69%, respectively. The 15N distribution ratios of the aboveground parts were higher than those of belowground parts in all treatments except the control. Straw additions could obviously increase the contents of organic matter and total nitrogen in soil and increase C/N ratio of soil organic matter. The correlation analysis showed that the C/N ratio of soil organic matter was significantly negatively correlated with the Ndff value of the belowground parts, as well as in the whole plant. Our findings suggest that it is better to apply nitrogen at rates between 200 and 300 mg·kg-1when corn straw is added into orchard soil.

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    Cited: CSCD(4)
      
    Seasonal variation of water sources for plants growing on continuous rock outcrops in limestone area of Southwest China
    NIE Yun-Peng, CHEN Hong-Song, WANG Ke-Lin
    Chin J Plant Ecol    2011, 35 (10): 1029-1037.   DOI: 10.3724/SP.J.1258.2011.01029
    Abstract2305)   HTML4)    PDF (466KB)(2042)       Save

    Aims Woody plants in karst regions often grow on the continuous rock outcrops. However, the source of water for these plants is unclear. This study aimed at investigating the seasonal variation of water sources for plants growing on continuous limestone outcrops in southwestern China.
    Methods Stable isotope techniques were used to access plant water uptake patterns for five different species in both wet and dry seasons. Then the IsoSource model was used to determine the probable contribution of each potential water source to total plant water uptake.
    Important findings In the wet season, an average of >80% of water for four of the five species came from rainwater received in the previous 15 days and stored in fissures in shallow layers. Water accessed by the other species came mostly from recent rainwater; however, the species simultaneously absorbed water from fissures in deep layers that had been recharged from previous precipitation. In the dry season, all five species utilized both recent and previous rainwater, and the two tree species and one large evergreen shrub species used more previous rainwater (>50%).

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    Cited: CSCD(31)
      
    Water-use strategies of two desert plants along a precipitation gradient in northwestern China
    ZHOU Ya-Dan, CHEN Shi-Ping, SONG Wei-Min, LU Qi, LIN Guang-Hui
    Chin J Plant Ecol    2011, 35 (8): 789-800.   DOI: 10.3724/SP.J.1258.2011.00789
    Abstract3256)   HTML13)    PDF (722KB)(2802)       Save

    Aims In arid and semiarid regions, precipitation is the most important water source for plants. Our objective was to investigate the water-use strategies of two dominant desert plants along a precipitation gradient in northwestern China.

    Methods We determined stable hydrogen and oxygen isotope compositions of the stem water from Artemisia ordosicaand Nitraria tangutorum and potential water sources (rain water, groundwater and soil water) at three study sites with different annual precipitation (Hanggin Banner and Dengkou County of Inner Mongolia Autonomous Region and Minqin County of Gansu Province). The IsoSource model was then used to calculate probable contributions of potential water sources to total plant water uptake. We also determined foliar carbon isotope ratios and free proline contents of both species to indicate water use efficiency and osmotic-adjustment ability.

    Important findings At the Hanggin Banner site (highest annual precipitation), both species obtained the highest proportion of water from shallow soil water and A. ordosicatook up water mostly from the 0-50 cm soil layer. However, they depended mainly on deep soil water or groundwater at the Dengkou and Minqin sites with lower annual precipitation. The water use efficiency of both species decreased with increasing annual precipitation. There was a positive correlation between carbon isotope ratio and free proline content in A. ordosica. These results suggest that desert plants can adjust their capabilities for up-take from different water sources and other physiological properties with variation in natural precipitation, but the strategies are species-specific.

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    Cited: CSCD(42)
      
    Relationships between foliar stable carbon isotope composition and environmental factors and leaf element contents of Pinus tabulaeformis in northwestern China
    LI Shan-Jia, ZHANG You-Fu, CHEN Tuo
    Chin J Plant Ecol    2011, 35 (6): 596-604.   DOI: 10.3724/SP.J.1258.2011.00596
    Abstract2240)   HTML4)    PDF (10101KB)(1936)       Save

    Aims Our objective was to analyze relationships between foliar stable carbon isotope composition (δ13C) and environmental factors and leaf element contents in Pinus tabulaeformis, which is widely distributed in northwestern China.

    Methods Leaf samples were taken in ten natural populations of P. tabulaeformis from Gansu, Ningxia and Inner Mongolia. The δ13C was determined using an isotope mass spectrometer. Environmental factors were recorded by Magellan GPS320 and from nearby weather stations. Leaf element contents were measured with low vacuum scanning electron microscope and X-ray energy dispersive spectroscopy. Carbon content was estimated with the potassium dichromate method, and nitrogen content was measured with the micro-Kjeldahl method. Data were evaluated with Excel 2003 and SPSS 13.0 analysis of correlation and regression.

    Important findings Foliar δ13C ranged from -28.68‰ to -25.02‰, with an average value of -26.82‰. Foliar δ13C did not closely correlate with altitude and longitude, but was significantly positively correlated to latitude and negatively correlated with annual mean precipitation and temperature. Therefore, δ13C in different natural populations of P. tabulaeformis is significantly influenced by environmental factors, and annual mean temperature and precipitation are essential factors in δ13C’s capability of fractionation and growth. Leaf N, P and K content were significantly negatively correlated with δ13C; however, Si, Ca and Fe content were significantly positively correlated with δ13C. Different δ13C in different natural populations reflects changes in plant nutrient element content. Response mode of climatic factors and element content under different habitat conditions reflected and affected properties of δ13C change in natural populations of P. tabulaeformis.

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    Cited: CSCD(20)
      
    Stable carbon isotope ratio (δ13C) in flag leaves of different genotypes of winter wheat and its relation to yield and water use efficiency
    FAN Ting-Lu, MA Ming-Sheng, WANG Shu-Ying, LI Shang-Zhong, ZHAO Gang
    Chin J Plant Ecol    2011, 35 (2): 203-213.   DOI: 10.3724/SP.J.1258.2011.00203
    Abstract2571)   HTML5)    PDF (561KB)(2091)       Save

    Aims Our objectives were to analyze differences of grain yield, water use efficiency (WUE) and stable carbon isotope ratio (δ13C) in various genotypes of dryland winter wheat (Triticum aestivum) and the correlation between δ13C value and grain yield and WUE under two different ecological conditions. Findings will help clarify the reliability of using δ 13C to evaluate WUE and provide a basis for breeding water-saving types.
    Methods We studied 15 winter wheat genotypes (12 from north China and 3 from Texas, USA) on the Loess Plateau of East Gansu under dryland and supplemental irrigation treatments at the jointing stage.
    Important findings Different genotypes had considerable differences in grain yield, WUE and δ 13C value whether under dryland or irrigation, and the δ 13C value increased with grain filling proceeding. Moreover, the δ 13C value under dryland condition was higher than under limited irrigation. The correlation between δ 13C with grain yield and WUE is significant during the grain filling stages whether under dryland or irrigation, and the correlation under dryland is better than that under limited irrigation. With irrigation of 100 mm water at jointing stage, various genotypes of winter wheat had significant compensation or super compensation effects. The δ 13C value can indicate WUE well whether under dryland or irrigated condition. Therefore, the δ 13C value can be used by breeding programs as a potential selection criterion for grain yield and WUE in wheat.

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    Cited: CSCD(5)
      
    Carbon isotope composition (δ13C) of C3 plants and water use efficiency in China
    REN Shu-Jie, YU Gui-Rui
    Chin J Plant Ecol    2011, 35 (2): 119-124.   DOI: 10.3724/SP.J.1258.2011.00119
    Abstract2909)   HTML15)    PDF (390KB)(2973)       Save

    Aims There have been many studies of carbon isotope composition (δ13C) of C3 plants in China, and δ13C has been widely used as an index of water use efficiency (WUE); however, most studies focused on single sites or small regions. Therefore, our objective was to study the spatial pattern of δ13C, the relationships between δ 13C and climate factors and whether δ 13C can represent WUE in large regions.
    Methods We obtained leaf δ 13C for 478 C3 species from 187 sites in China based on the literature.
    Important findings The range of δ13C was from -33.50‰ to -22.00‰, and the mean was -(27.10‰ ± 1.70)‰. There were significant differences among δ13C of grasses, shrubs and trees, with grasses having the highest value and trees the lowest. The result was different from studies in single sites and small regions. For different phylogenic plants, δ 13C of seed plants was significantly higher than ferns, the difference between gymnosperms and angiosperms was not statistically significant and monocotyledons had significantly higher values than dicotyledons. Leaf δ 13C had irregular variation with increasing longitude, but significantly increased with increasing latitude. Leaf δ 13C significantly increased with mean annual temperature and decreasing mean annual precipitation. The relationship between δ 13C and precipitation was similar to that of WUE and precipitation, so we conclude that δ 13C of C3 plants can be used as an index of WUE in large regions as well as in single sites or small regions.

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    Cited: CSCD(40)
      
    A review of applications of sulfur stable isotope technology in ecological studies
    WANG Yan-Hong, JIANG Hong, YU Shu-Quan, LI Wei, LIN Xi-Qiao
    Chin J Plant Ecol    2010, 34 (2): 179-185.   DOI: 10.3773/j.issn.1005-264x.2010.02.009
    Abstract2781)   HTML5)    PDF (361KB)(2295)       Save

    With the increase of anthropogenic SO2 emission, behavior of sulfur isotopes during biogeochemical processes has been the focus of numerous studies. We reviewed the potential contributions of studies using sulfur stable isotope, which include studies on 1) sources of sulfur in atmospheric processes, 2) sulfur dynamics in forest, farmland and aquatic ecosystems, 3) additions of sulfur stable isotope in ecological systems and 4) acid rain research in China. Furthermore, we made suggestions on future research, proper analysis methods and source partitioning models using sulfur stable isotopes.

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    Cited: CSCD(6)