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Table of Content
    Volume 44 Issue 6
    20 June 2020
    Desert riparian vegetation landscape in Ruoqiang, Xinjiang, China (Photographed by LI Jun-Li). The Populus euphratica are distributed along the river channel in the lower reaches of Tarim River. Due to the differences of groundwater levels, the phenology of Populus euphratica is quite different. The Populus euphratica trees close to the river are green, while those far away from the river have turned yellow; [Detail] ...
    A review on the effects of nitrogen and phosphorus addition on tree growth and productivity in forest ecosystems
    FENG Ji-Guang, ZHU Biao
    Chin J Plant Ecol. 2020, 44 (6):  583-597.  doi:10.17521/cjpe.2019.0176
    Abstract ( 2612 )   Full Text ( 197 )   PDF (2242KB) ( 1672 )   Save
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    Nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities and atmospheric N and P deposition have largely increased the availability of soil N and P in terrestrial ecosystems, which have considerably affected terrestrial carbon cycling processes. Tree growth and productivity in forest ecosystems play an important role in global carbon cycling, and determine the magnitude and direction of terrestrial carbon sequestration. Currently, a large number of field manipulation experiments have been conducted to investigate the effects of N and/or P addition on tree growth and forest productivity, but the results from these studies were inconsistent. Such inconsistent results might be affected by multiple factors, including biological, environmental and experimental variables. Here, we reviewed the present research status of the effects of N and P addition on tree growth and forest productivity in forest ecosystems based on three aspects, including the number of publications and experiments with field N and P addition, and the global distributions of these experiments. Then, we summarized the methods for assessing tree growth and forest productivity at ecosystem level in forest ecosystems, including relative growth rate and absolute increment. According to the related results, we reviewed the regulating factors that affect tree growth and productivity, and the potential mechanisms for such factors, including climate, tree size and stand age, plant functional traits (including type of tree-associated mycorrhizal fungi, N-fixation property of trees, and conservative and acquisitive functional traits), plant-microbe interaction, ambient nutrient (i.e., N and P) deposition rate, and experimental variables. Finally, we summarized the current studies, and pointed out five aspects that are urgently needed to provide further insights in future studies, including the physiological mechanism of how tree growth responds to N and P addition, the tradeoff and allocation among growth of various parts of tree under N and P addition, the role of plant functional traits in regulating and predicting the responses of tree growth to N and P addition, how the competition among trees regulates the responses of tree growth to N and P addition, and conducting long-term and coordinated distributed field experiments investigating the effects of N and P addition on tree growth and forest productivity at the global scale.

    Research Articles
    Forest species diversity mapping based on clustering algorithm
    YI Hai-Yan, ZENG Yuan, ZHAO Yu-Jin, ZHENG Zhao-Ju, XIONG Jie, ZHAO Dan
    Chin J Plant Ecol. 2020, 44 (6):  598-615.  doi:10.17521/cjpe.2019.0347
    Abstract ( 1221 )   Full Text ( 138 )   PDF (14036KB) ( 1176 )   Save
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    Aims Monitoring forest species diversity continuously and efficiently is important to maintain ecosystem services and achieve sustainability and conservation goals. In this paper, we explored the relationship between leaf biochemical and spectral properties and their inner linkage with species diversity, then estimated the forest species diversity based on a clustering algorithm using airborne imaging spectroscopy and Light Detection and Ranging (LiDAR) data in the Gutianshan National Nature Reserve of China.
    Methods Firstly, we isolated individual tree crowns (ITCs) with the watershed algorithm from the LiDAR data. Then we calculated the optimal vegetation indices (VIs) representing the key biochemical properties from the hyperspectral data and selected optimal structural parameters from commonly used LiDAR-derived structural parameters based on correlation and stepwise regression analysis with the field samples. Finally, a self-adaptive Fuzzy C-Means (FCM) clustering algorithm was applied to map the species diversity (i.e. Richness, Shannon-Wiener index and Simpson index) in the study area for each 20 m × 20 m moving window.
    Important findings The results indicated that biochemical components (chlorophyll a & b, total carotenoids, equivalent water thickness, specific leaf area, cellulose, lignin, nitrogen, phosphorus and carbon) could be well quantified by leaf spectrum using partial least squares regression (R2 = 0.60-0.79, p < 0.01), and represented by hyperspectral VIs, namely, Transformed Chlorophyll Ratio Index/Optimization of Soil-adjusted Vegetation Index (TCARI/OSAVI), Carotenoid Reflectance Index (CRI), Water Band Index (WBI), Ratio Vegetation Index (RVI), Photochemical Reflectance Index (PRI) and Canopy Chlorophyll Concentration Index (CCCI). The individual tree isolation showed high accuracy (R 2 = 0.77, RMSE = 16.48). The correlation and stepwise regression analysis showed tree height and skewness were the optimal structural parameters among seven commonly used forest structural parameters (R 2 = 0.32, p < 0.01). The species diversity indices calculated from the self-adaptive FCM clustering algorithm based on the six VIs and two optimal structural parameters correlated well with the field measurements (species richness, R 2 = 0.56, RMSE = 1.81; Shannon-Wiener index, R 2 = 0.83, RMSE = 0.22; Simpson index, R 2 = 0.85, RMSE = 0.09). With the clustering method combined with crown-by-crown variations in hyperspectral biochemical VIs and LiDAR-derived structural parameters, we created continuous maps of forest species diversity in the examined subtropical forest without the need to identify specific tree species. Our case study in Gutianshan showed the potential of airborne hyperspectral and LiDAR data in mapping species diversity of the subtropical evergreen broad-leaved forest. It could also provide a pathway for monitoring the state and changes of forest biodiversity at regional scales.

    Temporal areal changes of wetlands in the lower reaches of the Tarim River and their responses to ecological water conveyance
    YU Liang, LI Jun-Li, BAO An-Ming, BAI Jie, HUANG Yue, LIU Tie, SHEN Zhan-Feng
    Chin J Plant Ecol. 2020, 44 (6):  616-627.  doi:10.17521/cjpe.2019.0267
    Abstract ( 855 )   Full Text ( 130 )   PDF (2205KB) ( 432 )   Save
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    Aims Ecological water conveyance is of great importance for desert riparian wetland ecosystem. However, few studies have been focused on the quantitative evaluation of water conveyance to wetland restoration due to a lack of continous observation data. This paper analyzed the temporal wetland area changes between Yengisu and Alagan in the lower reach of Tarim River based on time series remote sensing data during 2000-2018, and evaluated the effects of ecological water conveyance on wetland restoration, so as to guide the ecological water conveyance and maintain the stability of the desert wetland ecosystem.
    Methods About 354 Landsat ETM+/TM/OLI, Sentinel 2 images during 2000-2018 were used to map the monthly wetland area changes in the lower reach of Tarim River, then their annual, seasonal and spaital areal changes were analyzed. The correlation between wetland area changes and ecological water conveyance, underground water levels were also evaluated based on Pearson correlation and cross-correlation methods.
    Important findings The wetland area has steadly increased in the last 19 years. The areal change rate was minor before 2011 while rapidly increased after 2011. The wetland expanded at a high rate during 2011-2013 and 2017-2018. Different ecological water volumes and water conveyance patterns (single channel or dual channel) can explain different areal changing rates at different stages. The correlation analysis between wetland area changes and ecological water volumes showed that the accumulative ecological water volume is the primary reason causing wetland expansion in recent years. In order to maintain a steady improvement of wetland vegetation, more than 350 million square meters of ecological water are conveyed to the downstream of the Tarim River through dual channel. When the groundwater depth is maintained between -5.0- -3.5 m, the wetland vegetation can sustain a good growth condition.

    Spatio-temporal characteristics of vegetation water use efficiency and their relationships with climatic factors in alpine and subalpine area of southwestern China
    ZHOU Xiong, SUN Peng-Sen, ZHANG Ming-Fang, LIU Shi-Rong
    Chin J Plant Ecol. 2020, 44 (6):  628-641.  doi:10.17521/cjpe.2019.0281
    Abstract ( 1085 )   Full Text ( 117 )   PDF (3897KB) ( 712 )   Save
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    Aims Water use efficiency (WUE) is an important indicator for understanding the coupling and trade-off relationships between ecosystem water and carbon cycles. In order to reveal the response and adaptation characteristics of different vegetation types to climate change regionally, we examined the trends, altitudinal distributions, and spatial variations of WUE in nine vegetation types in the alpine and subalpine area of southwestern China during the period of 2000-2014.
    Methods We estimated the vegetation WUE using Moderate Resolution Imaging Spectroradiometer (MODIS) gross primary production (GPP) and evapotranspiration (ET) products, and the gridded climate data interpolated from Aunsplin. Trend analysis and correlation analysis were conducted to examine the relationships between vegetation WUE and other factors, including air temperature, precipitation, and elevation.
    Important findings The results showed that: (1) The average annual WUE in the study region was 0.95 g·m-2·mm-1 with a significantly increasing trend at 0.011 g·m-2·mm-1·a-1 from 2000 to 2014. The average WUE showed a pattern of higher in the southeast region but lower in the northwest region, and the WUE was found increased in 85.84% of study area. (2) The average WUEs were increasing in all vegetation types, and the WUEs showed a gradient of evergreen needleleaf forest > savannas > evergreen broadleaf forest > woody savannas > cropland > deciduous broadleaf forest > mixed forest > closed shrublands > grassland. (3) The WUE was positively correlated with air temperature in 89.56% of the study area, but it was negatively correlated with precipitation in 92.54% of the study area. The highest correlation between WUE and air temperature was found in grassland, while the highest correlation between WUE and precipitation was identified in woody savannas. (4) As the regional climax vegetation type in southwestern China, the evergreen needleleaf forest’s WUE has high adaptation abilities to both altitudinal change and climate change.

    Defense strategies of dominant plants under different grazing intensity in the typical temperate steppe of Nei Mongol, China
    LI Ying, GONG Ji-Rui, LIU Min, HOU Xiang-Yang, DING Yong, YANG Bo, ZHANG Zi-He, WANG Biao, ZHU Chen-Chen
    Chin J Plant Ecol. 2020, 44 (6):  642-653.  doi:10.17521/cjpe.2019.0329
    Abstract ( 1426 )   Full Text ( 136 )   PDF (1343KB) ( 863 )   Save
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    Aims Grazing is one of the main grassland using modes, which has caused certain biotic stress on pasture. In order to survive, pasture initiates defense mechanisms by regulating the primary and secondary metabolic processes. This article aims to 1) figure out the distribution of defensive substances in different organs produced by the dominant plants Stipa grandis and Leymus chinensis; 2) explore the similarities and differences of the defense mechanisms and carbon-nitrogen trade-off strategies in S. grandis and L. chinensis.
    Methods We conducted a different grazing intensity experiment in the typical temperate steppe of Nei Mongol. The lignin and secondary metabolites, such as tannins, flavonoids, phenols and alkaloids, as well as the ratio of carbon and nitrogen in different organs of the dominant plants S. grandis and L. chinensis were investigated.
    Important findings Our results showed that S. grandis and L. chinensis produced a large number of secondary metabolites such as tannins, flavonoids, phenols and alkaloids in the face of grazing stress. The leaves were the main synthesis and storage organs. In addition, the chemical defense mechanism of L. chinensis was well induced and expressed under moderate grazing. There was no significant increase in the lignin content in the aboveground parts of S. grandis and L. chinensis. Therefore, both of them were more inclined to chemical defense than mechanical defense in the mechanism of avoiding grazing. Because of the higher nitrogen use efficiency of L. chinensis, it could be protected by both carbon and nitrogen metabolic pathways. However, Stipa grandis did not efficiently distribute nitrogen into chemical defense in the early stages of growth. More resources still used for primary metabolism in the early stage of S. grandis and L. chinensis growth, under light grazing stress, which increased their grazing resistance. Therefore, light grazing is conducive to improving the carbon and nitrogen use efficiency of pasture, and improving ecosystem productivity and stability.

    Effects of endophyte fungal species and host plant genotype on the leaf shape and leaf area of endophyte-grass symbionts
    QIN Tian-Zi, REN An-Zhi, FAN Xiao-Wen, GAO Yu-Bao
    Chin J Plant Ecol. 2020, 44 (6):  654-660.  doi:10.17521/cjpe.2020.0037
    Abstract ( 644 )   Full Text ( 112 )   PDF (933KB) ( 354 )   Save
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    Aims Epichloë infection can play an important role in the growth and development of host plants. However, few studies have been reported on the effects of endophyte infection on leaf shape and area of host plants.
    Methods Our study used Achnatherum sibiricum as experimental material, and explored the effects of endophyte species and host plant genotype on the leaf shape and area of A. sibiricum-endophyte symbionts through the combination of the length and width method with the revised correction coefficient and the scanning calculation method.
    Important findings Endophyte infection status, endophyte species and host plant genotype had no significant influences on the correction coefficient of leaf size calculation, leaf length, leaf width and leaf length-width ratio reflecting leaf shape. By calculation and verification, we determined that the correction coefficient of leaf size calculation of A. sibiricum was 0.594 9. There was no significant difference between the leaf areas measured by length and width method with the revised correction coefficient and the scanning calculation method. In addition, the leaf areas measured by two methods were not significantly affected by endophyte infection, endophyte species and plant maternal genotype.

    Spatial genetic structure of Lycium ruthenicum in the Qaidam Basin
    WANG Chun-Cheng, MA Song-Mei, ZHANG Dan, WANG Shao-Ming
    Chin J Plant Ecol. 2020, 44 (6):  661-668.  doi:10.17521/cjpe.2019.0298
    Abstract ( 773 )   Full Text ( 113 )   PDF (1373KB) ( 494 )   Save
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    Aims Based on the cpDNA sequences, we studied the genetic diversity, genetic structure and haplotype evolution of wild Lycium ruthenicum in the Qaidam Basin and provided the scientific basis for the genetic conservation of this species.
    Methods We used three filtered high polymorphic cpDNA fragments (psbA-trnH, psbK-psbI and trnV) to study the genetic variation pattern of L. ruthenicum in the Qaidam Basin by employing the population genetic analysis methods. The molecular diversity indices were calculated by using the software of DnaSP 6.0 and Permut 2.0. Genetic differentiation among populations and the defined groups was estimated by the AMOVA analysis. The median-joining network and principal coordinate analysis (PCoA) were used to identify the clustering relationship of haplotype. The maximum likelihood method and Bayesian method were used to reconstruct the phylogenetic tree based on cpDNA haplotypes.
    Important findings The combined length of psbA-trnH, psbK-psbI and trnV was 1 454 bp. 14 polymorphic sites were detected, and a total of seven haplotypes were identified. The total genetic diversity (hT) and within-population genetic diversity (hS) were 0.916 and 0.512, respectively. Results from AMOVA suggested that more than 80% of the observed variation was due to differences among groups and populations. The maximum likelihood analysis and Beast analysis revealed that seven haplotypes clustered into two clusters, corresponding to Golmud and Delingha regions and Nuomuhong region, respectively. The revealed topological structure and clusters of haplotype network and PCoA analyses were consistent with the phylogenetic trees. Results of the Mantel test (r = 0.591 1, p = 0.000 9) indicated a non-significant correlation between geographical distance and genetic distance. The L. ruthenicum populations in the Qaidam Basin have high levels of genetic diversity and significant genetic differentiation among populations. In relation to conservation management, we identified the Nuomuhong forestry station and Xinle Village of Golmud City as having a high degree of genetic diversity and these should be the areas of the greatest focus for conservation.

    Extreme drought effects on nonstructural carbohydrates of dominant plant species in a meadow grassland
    SONG Lin, LUO Wen-Tao, MA Wang, HE Peng, LIANG Xiao-Sa, WANG Zheng-Wen
    Chin J Plant Ecol. 2020, 44 (6):  669-676.  doi:10.17521/cjpe.2019.0331
    Abstract ( 1287 )   Full Text ( 46 )   PDF (975KB) ( 848 )   Save
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    Aims Plant nonstructural carbohydrates (NSCs) produced by photosynthesis can reflect the responses of plants and/or ecosystem to environmental changes. Climate models recently predicted an increase in the frequency and duration of extreme drought (ED) events that could profoundly impact ecosystem structure and functions. Yet, less is understood about the response patterns of different plant species and functional groups to extreme drought.
    Methods Here we studied the effects of extreme drought on the NSCs of dominant species belonging to different functional groups in grasslands. To achieve ED, we experimentally reduced precipitation amounts by 66% during four consecutive growing seasons in a meadow steppe in Hulunbeier, North China. The NSCs of six plants grouped into two functional groups (i.e., grass and non-grass) were examined.
    Important findings We found different species responded differently to drought, due to their differences in plant biological characteristics, photosynthetic characteristics and physiological ecology. This result implied that different species used different NSC-use strategies to cope with drought stress, resulting in different responses of their biomass to extreme drought. Extreme drought significantly increased the starch concentrations, and had no effect on the soluble sugar concentrations of the grass functional group. Contrarily, ED significantly increased the soluble sugar concentrations, and had no significant effects on the starch concentrations of the non-grass functional group. These results indicate that grasses moderately use and store photosynthate to cope with drought stress, hence their biomass was less sensitive. The biomass of the non-grasses was more sensitive perhaps because they maximally utilize soluble sugar for plant growth, defense and reproduction. Our results showed that different species or functional groups exhibit different NSC-use strategies to cope with drought stress. This study could provide scientific data for predicting future ecosystem responses to extreme drought.

    Effects of drought stress on photosynthesis, growth and root structure of transgenic PtPIP2;8 poplar 84K (Populus alba × P. glandulosa)
    LIU Li-Yan, FENG Jin-Xia, LIU Wen-Xin, WAN Xian-Chong
    Chin J Plant Ecol. 2020, 44 (6):  677-686.  doi:10.17521/cjpe.2020.0058
    Abstract ( 927 )   Full Text ( 70 )   PDF (1220KB) ( 575 )   Save
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    Aims In this study, changes in growth, photosynthesis and root structure in response to drought were tested in transgenic poplar 84K (Populus alba × P. glandulosa) seedlings with different expression levels of aquaporin gene (PtPIP2;8). The function of aquaporin gene PtPIP2;8 and its response to drought stress were analyzed.
    Methods We selected PtPIP2;8 silencing line of poplar 84K, PtPIP2;8 overexpressing line of poplar 84K and wildtype (WT) as the experimental materials. The Real-time fluorescence quantitative PCR technique was used to detect the PtPIP2;8 expression in roots, stems and leaves. Root hydraulic conductance was measured by high pressure liquid flow meter. The photosynthetic light-response curve, and gas exchange parameters were measured by a LI-6400 photosynthetic system. Growth indexes were determined, and the root length, root surface area, root volume and total root tips were scanned and then analyzed with the root analysis software.
    Important findings The results showed that: (1) The gene PtPIP2;8 was mainly expressed in the root system in WT, while its significant expression occurs not only in roots, but also in stems and leaves in PtPIP2;8 overexpressing poplar lines. The PtPIP2;8 RNAi-silence poplar lines only showed weak expression of PtPIP2;8 in the root, and the expression level were 1/20 and 1/80 of WT and overexpression line, respectively. (2) The root structure analysis showed that overexpression lines had significantly lower total root length, total root surface area, total root volume and total root tips than RNAi-silence line and WT, but higher root hydraulic conductance compared with RNAi-silence line and WT. These results showed that the aquaporin gene PtPIP2;8 participated in plant water transport and improved water transport efficiency. (3) Under normal water conditions, RNAi-silence lines showed lower plant height and leaf area but higher root-shoot ratio compared with overexpression line and WT. After drought stress, RNAi-silence lines only slightly decreased the net photosynthetic rate (Pn) and stomatal conductance (Gs), and maintained a relatively high Pn. Diurnal changes of Pn and Gs in RNAi-silence lines showed a single-peak pattern, in which the decrease of photosynthesis was caused by stomatal limitation. Diurnal changes of Pn in both overexpression lines and WT had a two-peak pattern, indicating the non-stomatal limitation of photosynthesis. Drought stress slightly decreased Pn of RNAi-silence lines, while largely decreased Pn of overexpression line and WT decreased, especially at 13:00 and 15:00, indicating that overexpression line and WT were more sensitive to drought stress compared with the RNAi-silence lines. (4) Under drought stress, RNAi-silence line showed the least decline in relative growth rate and total biomass, and the highest root-shoot ratio among the three poplar lines. The total root surface area, total root volume and total root tips of RNAi-silence line were significantly higher than those of WT. The results suggest that aquaporin gene PtPIP2;8 directly participates in the water transport and helps to improve the water transport efficiency, thus the transformation of aquaporin PtPIP2;8 gene may affect root development and growth of plants. Overexpression lines weaken their drought resistance with decreased root development and increased leaf area, while RNAi-silence line increases its drought resistance with reduced leaf area, increased root growth and root-shoot ratio. The results of this study indicate that aquaporin improves the efficiency of water transport across membranes, while the non-aquaporin water-conducting mechanism has greater tolerance to drought.

    Spatial variation and controlling factors of temperature sensitivity of soil respiration in forest ecosystems across China
    ZHENG Jia-Jia, HUANG Song-Yu, JIA Xin, TIAN Yun, MU Yu, LIU Peng, ZHA Tian-Shan
    Chin J Plant Ecol. 2020, 44 (6):  687-698.  doi:10.17521/cjpe.2019.0300
    Abstract ( 1814 )   Full Text ( 130 )   PDF (2321KB) ( 1225 )   Save
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    Aims Our objective was to determine the spatial variation of the temperature sensitivity of soil respiration (Q10) and it’s controlling factors in forest ecosystems across China.
    Methods Based on published papers, the field measurement data of soil respiration were collected to build the dataset of annual Q10 in forest ecosystems across China. Further, the spatial variation and the drivers of Q10 in different forest types were analyzed.
    Important findings The results showed that 1) Q10 ranges from 1.09 to 6.24, with a mean value (± standard error) of 2.37 (± 0.04) and no significant difference among different forest types; 2) When all forest types were considered, Q10 increased with increasing latitude, altitude, soil organic carbon content (SOC) and soil total nitrogen content (TN), but decreased with increasing longitude, mean annual temperature (MAT) and mean annual precipitation (MAP). Climate (MAT, MAP) and soil (SOC, TN) factors together explained 32.8% variations in Q10. MAT and SOC were considered as the primary factors driving the spatial variation of Q10. 3) Q10 of different forest types responded differently to climate and soil factors. Q10 decreased with the increase of MAP in the deciduous needleleaf forest (DNF), while Q10 showed no significant correlation with MAP in other forest types. Q10 increased with the increase of TN in evergreen broadleaved forest (EBF), deciduous broadleaved forest (DBF), evergreen needleleaf forest (ENF), and the sensitivity of Q10 to TN was the highest in EBF and the lowest in ENF. Although Q10 showed concentrated distribution trend, more attention should be paid to the large range of variation in future C budget studies. The primary driving factors and the response to environmental factors of Q10 varied among forest types. Under the scenario of future climate change, Q10 may vary divergently among different forest types. Therefore, the divergent responses of key parameters of carbon cycle in different forest types to climate change should also be considered in future carbon-climate models.

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