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Table of Content
    Volume 38 Issue 1
    01 January 2014

    Mechanisms of rhizosphere priming effects. Sun et al. overviewed the mechanisms of rhizosphere priming effects and their ecological significance (Pages 62–75 of this issue) (Drawn by SUN Yue).

      
    Research Articles
    Spatio-temporal patterns of precipitation-use efficiency of vegetation and their controlling factors in Inner Mongolia
    MU Shao-Jie, ZHOU Ke-Xin, QI Yang, CHEN Yi-Zhao, FANG Ying, and ZHU Chao
    Chin J Plan Ecolo. 2014, 38 (1):  1-16.  doi:10.3724/SP.J.1258.2014.00001
    Abstract ( 715 )   PDF (850KB) ( 1321 )   Save
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    Aims Precipitation-use efficiency (PUE) is an important indicator for understanding how net primary productivity (NPP) in arid and semi-arid ecosystems responds to variations in precipitation. The objective of this study was to determine the spatio-temporal patterns and responses to climatic and biotic factors of PUE at a regional scale.
    Methods CASA (Carnegie-Ames-Stanford Approach) model was used to simulate NPP in Inner Mongolia during 2001–2010 based on the MOD13A1 data and spatially interpolated meteorological data. PUE was calculated as the ratio of NPP to annual precipitation. The effects of fraction of vegetation cover (FVC) and leaf area index (LAI) on PUE were also investigated. The FVC was calculated with the dimidiate pixel model based on the MOD13A1 data. LAI data were acquired as the MODIS LAI products.
    Important findings The multi-year average PUE of Inner Mongolia was 0.94 g C·m–2·mm–1, exhibiting apparent increasing trend at an average rate of 0.55 g C·m–2·mm–1 per 10° with changes in longitude from 105° E to 120° E. The spatial patterns of PUE showed significant differences among vegetation types. The PUE was highest in shrubs and lowest in desert. The spatial distribution of PUE responded differentially to climatic factors in different precipitation ranges. Where precipitation was less than 75 mm, PUE showed a significant negative correlation with temperature and precipitation (R2 = 0.226, p < 0.05). In the area with precipitation of 175–300 mm, PUE exhibited a significant positive correlation with temperature and precipitation (R2 = 0.878, p < 0.001), and increased significantly (R2 = 0.94, p < 0.001) with precipitation at a rate of 0.57 g C·m–2·mm–1 per 100 mm. In the area where precipitation was higher than 475 mm, PUE increased spatially with increasing temperature and decreasing precipitation. In this precipitation range, the effect of temperature on spatial variance of PUE was 8.61 times of that of precipitation. The inter-annual variation of PUE also had different responses to climatic factors in different precipitation ranges. Where precipitation was less than 220 mm, PUE displayed a positive correlation with precipitation and a negative correlation with temperature. In the area with precipitation of 220–310 mm, precipitation had a much greater effect than temperature on the inter-annual variations of PUE. Where precipitation was higher than 310 mm, PUE showed positive correlations with both temperature and precipitation. In relatively humid parts of this precipitation range, however, the PUE showed a poor correlation with precipitation, but a stronger correlation with temperature. FVC was linearly related with the spatial distribution (R2 = 0.73, p < 0.001) and inter-annual variations of PUE (R2 = 0.11, p < 0.001). LAI showed a linear relationship with the inter-annual variations of PUE (R2 = 0.42, p < 0.001). In the area where LAI was less than 3.15 and with non-forest vegetation, LAI was linearly related with the spatial distribution of the PUE.

    Characteristics of soil seed banks and their relationships with aboveground vegetation in ditches in the Sanjiang Plain
    LIU Qing-Yan, WANG Guo-Dong, JIANG Ming, Lü Xian-Guo, and LOU Yan-Jing
    Chin J Plan Ecolo. 2014, 38 (1):  17-26.  doi:10.3724/SP.J.1258.2014.00002
    Abstract ( 483 )   PDF (334KB) ( 1536 )   Save
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    Aims Ditches play an important role in preserving plant biodiversity. Our objective was to determine the characteristics of soil seed banks and their relationships with aboveground vegetation in ditches over different times in the Sanjiang Plain.
    Methods Soil seed banks were investigated on different sites of ditches, and germination method was used to identify species composition of seed banks. Aboveground vegetation was investigated with quadrate method in ditches where seed banks were sampled.
    Important findings Results showed that the seed density in the soil seed banks in ditches was generally high. Seed density on the banks of ditches was 8 973–25 000 seeds·m–2, higher than that in the sediments of ditches, which was 506–1 488 seeds·m–2. A total of 50 species were identified in the soil seed banks with the germination method, belonging to 41 genera in 20 families. The number of species found in the soil seed banks was 37, 34, and 33 in ditches with excavation time history of 10 years, 20 years, and 30 years, respectively, corresponding to 25, 33, and 22 species recorded in the aboveground vegetation. Similarity indexes for the comparison between soil seed banks and aboveground vegetation were 38.7%, 35.8%, 32.7%, respectively. Simpson index, Shannon-Wiener index and Pielou evenness index of aboveground vegetation increased with succession. According to this study, there are a large amount of wetland species in the soil seed bank and aboveground vegetation in ditches in the Sanjiang Plain, indicating that ditches play an important role in preserving plant biodiversity and that soil seed bank in ditches have potential to be used in wetland restoration. Plant community degradation with succession in ditches suggests that management of ditches should be strengthened.

    Effects of simulated nitrogen deposition on root exudates and phosphorus efficiency in Pinus massoniana families under low phosphorus stress
    PANG Li, ZHANG Yi, ZHOU Zhi-Chun, FENG Zhong-Ping, and CHU De-Yu
    Chin J Plan Ecolo. 2014, 38 (1):  27-35.  doi:10.3724/SP.J.1258.2014.00003
    Abstract ( 554 )   PDF (314KB) ( 1632 )   Save
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    Aims Atmospheric nitrogen (N) deposition largely increased in recent years, resulting in an increased N availability and N:P ratio in forest soils. The objective of this study was to determine the effects of simulated N deposition on P efficiency and root secreted acid phosphatase and organic acids in Pinus massoniana under low P stress.
    Methods Treatments included two P conditions, i.e. homogeneous low P availability vs. heterogeneous low P availability among soil layers, in combination with two N deposition levels in a two-year pot experiment. Four full-sib progenies collected from the second-generation breeding population of P. massoniana were used.
    Important findings Under both the homogeneous and heterogeneous low P conditions, N:P stoichiometric ratio in P. massoniana seedlings was significantly increased by simulated nitrogen deposition, which stimulated the amount of root acid phosphatase and organic acid secretion. The amount of root exudates was higher under the homogeneous low P condition than under the heterogeneous low P condition. The level of root secreted organic acids was significantly correlated with the growth in P. massoniana seedlings. Under the homogeneous low P condition, P acquisition efficiency and biomass in P. massoniana seedlings were not affected by simulated N deposition, mainly due to the high N:P ratios and low sensitivity to N addition; whereas under the heterogeneous low P condition, greater growth response to N addition was observed due to the higher N:P ratio. An increased root secretion of organic acids contributed to enhancement of P acquisition efficiency and growth under the high N deposition level. Significant variations among families in growth response to the simulated N deposition were observed. Under the homogeneous low P condition, seedlings in the family 71 × 20 were found to respond to the simulated N deposition with increased root organic acids and biomass. Under the heterogeneous low P condition, seedlings in the families of 36 × 29, 71 × 20, and 73 × 23 responded to the simulated N addition with increased biomass and root secretion.

    Root architecture and ecological adaptation strategies in three shelterbelt plant species in the southern Taklimakan Desert
    GUO Jing-Heng, ZENG Fan-Jiang, LI Chang-Jun, and ZHANG Bo
    Chin J Plan Ecolo. 2014, 38 (1):  36-44.  doi:10.3724/SP.J.1258.2014.00004
    Abstract ( 590 )   PDF (352KB) ( 1752 )   Save
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    Aims Root architectural properties influence the efficiency and cost of resource exploitation of plants. This paper aims to investigate the root topological properties and ecological adaptation strategies of three plant species which play important roles in wind shelterbelt in the southern Taklimakan Desert of China.
    Methods We excavated the coarse root systems of three shelterbelt plant species (Tamarix ramosissima, Haloxylon ammodendron, Populus alba var. pyramidalis) at a study site in the southern Taklimakan Desert and analyzed their root architectural properties, including topology, root length, diameter, and scaling relations.
    Important findings We found differences as well as similarities in the topological structure of root systems among the three plant species. The differences in root structure reflected different adaptation strategies among the plants to soil environment. The root branching order in both T. ramosissima (qa = 0.46, qb = 0.13, TI = 0.84, qa and qb show normed values corresponding to parameters a and b, respectively, TI shows topological index) and H. ammodendron (qa = 0.63, qb = 0.19, TI = 0.90) resembled the herringbone structure; whilst it was dichotomous in P. alba var. pyramidalis (qa = 0.03, qb = 0.02, TI = 0.49). The main root length in the three plant species was all very along. Longer root length could reduce the internal competition of roots for nutrients, so that plants were better cope with the resource-poor sandy soil environment. The Leonardo da Vinci theory is supported in this study with the three plant species.

    Analysis of soil respiration and components in Castanopsis carlesii and Cunninghamia lanceolata plantations
    WU Jun-Jun, YANG Zhi-Jie, LIU Xiao-Fei, XIONG De-Cheng, LIN Wei-Sheng, CHEN Chao-Qi, and WANG Xiao-Hong
    Chin J Plan Ecolo. 2014, 38 (1):  45-53.  doi:10.3724/SP.J.1258.2014.00005
    Abstract ( 512 )   PDF (329KB) ( 1586 )   Save
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    Aims Partitioning the soil respiration is an important step in understanding ecosystem-level carbon cycling. In addition, the heterotrophic and autotrophic components of soil respiration may respond differently to climate change. Our objectives were to evaluate the impact of soil temperature and water content on soil respiration and its components in Castanopsis carlesii and Cunninghamia lanceolata plantations, to determine the relative contributions of autotrophic and heterotrophic respiration to soil respiration, and to explore how different forest types would affect soil respiration and its components.
    Methods The study site is located in the Nature Reserve of Castanopsis kawakamii, Fujian Province, eastern China. By using a field setup through trenching method and LI-8100 open soil carbon flux system, the dynamics of soil respiration were measured from August 2012 through July 2013. Soil temperature at 5 cm depth and water content of the 0–12 cm soil layer were measured concurrently with the measurements of soil respiration. Relationships of soil respiration with soil temperature and water content were determined by fitting both an exponential model and a two-factor model.
    Important findings Soil respiration and its components showed significant correlations with soil temperature. There were significant monthly changes, in the form of a single-peaked curve, in soil respiration and its components in the two forest types. Soil temperature explained 70.3%, 73.4%, and 58.2% of the monthly variations in soil respiration, autotrophic respiration, and heterotrophic respiration, respectively, in the Castanopsis carlesii plantation; whilst it explained 77.9%, 65.7%, and 79.2% of the monthly variations in the three variables in the Cunninghamia lanceolata plantation. There was no significant relationship between soil respiration and soil water content in both forest types. The annual estimates of CO2 efflux through autotrophic respiration in the two types forests were 4.00 and 2.18 t C·hm–2·a–1, respectively, accounting for 32.5% and 24.1% of soil respiration. The annual estimates of CO2 efflux through heterotrophic respiration were 8.32 and 6.88 t C·hm–2·a–1, respectively, accounting for 67.5% and 75.9% of soil respiration. The annual estimates of CO2 efflux through soil respiration and partitioning of the components were all higher in the Castanopsis carlesii plantation than in the Cunninghamia lanceolata plantation.

    Effects of fungal endophyte infection on soil properties and microbial communities in the host grass habitat
    ZHOU Yong, ZHENG Lu-Yu, ZHU Min-Jie, LI Xia, REN An-Zhi, and GAO Yu-Bao
    Chin J Plan Ecolo. 2014, 38 (1):  54-61.  doi:10.3724/SP.J.1258.2014.00006
    Abstract ( 548 )   PDF (336KB) ( 1464 )   Save
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    Aims Leymus chinensis is a dominant grass native to the mid-eastern Inner Mongolia Steppe. The plants of this species are sometimes heavily infected with fungal endophytes that produce alkaloids, which in turn affect insect herbivory, plant production, and litter decomposition. Our objective was to investigate the effects of the L. chinensis-endophyte association on soil properties and soil microbial communities in field and pot experiments.
    Methods We concurrently conducted a field and a pot experiment. The soil total carbon (C) and nitrogen (N) were analyzed with an Elemental Analyzer, and C mineralization was determined by using a soil incubation test over a 30-day period. Soil microbial biomass and community composition were assayed by using phospholipid fatty acid (PLFA) technique.
    Important findings In the field experiment, where L. chinensis plants had grown for longer time and there was litter decomposition, fungal endophyte infection significantly increased soil N content, the initial C mineralization rate, the C mineralization during the first three days, and the accumulative C mineralization during the 30-day soil incubation. In the pot experiment, where L. chinensis plants had grown for shorter time and there was no litter decomposition, the soil total C and N contents and the C mineralization did not differ between the endophyte-infected (E+) and endophyte-free (E–) treatments. We found no significant difference in the types of PLFAs between the E+ and the E– treatments in both field and pot experiment, but endophyte infection tended to increase the soil microbial biomass. The PLFA contents of bacteria, gram-negative bacteria (G–), fungi, and total PLFA were significantly higher in the E+ treatment than in the E– treatment in the pot experiment; whereas in the field experiment, the PLFA contents of gram-positive bacteria (G+) and actinomycetes were significantly higher in the E+ treatment than in the E– treatment. This study suggests that endophyte infection may change the soil N accumulation and the rate of C mineralization, and alter soil microbial community structure. Our findings can help with understanding the relationship between fungal endophytes and L. chinensis and its role in ecosystem C and N cycling.

    Review
    Mechanisms of rhizosphere priming effects and their ecological significance
    SUN Yue, XU Xing-Liang, and Yakov KUZYAKOV
    Chin J Plan Ecolo. 2014, 38 (1):  62-75.  doi:10.3724/SP.J.1258.2014.00007
    Abstract ( 1178 )   PDF (446KB) ( 1634 )   Save
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    Priming effects are defined as “strong short-term changes in the turnover of soil organic matter caused by moderate treatments of the soil”. Rhizosphere is the most important place, where the priming effects take place. Rhizosphere priming effects reflect the turnover rate of soil carbon and nitrogen, and affect the acquisition of competition for nutrients by plants and microorganisms, thus maintaining nutrient balance among the various components of an ecosystem. Although there has been a general understanding on the occurrence of rhizosphere priming effects, the mechanisms underlying their role in soil carbon and nitrogen transformations and their ecological significance are still not fully comprehended. This paper provides a synthesis of the latest advancement in studies of the rhizosphere priming effects. On the basis of reviews of research history and identification of the hotspots, we first put forward a mechanism underlying the occurrence of rhizosphere priming effects, and then examined the biotic and abiotic factors influencing the rhizosphere priming effects. The ecological significance and outlooks of research in the rhizosphere priming effects were discussed and clarified.

    Gynomonoecy in angiosperms: phylogeny, sex expression and evolutionary significance
    Jannathan MAMUT and TAN Dun-Yan
    Chin J Plan Ecolo. 2014, 38 (1):  76-90.  doi:10.3724/SP.J.1258.2014.00008
    Abstract ( 582 )   PDF (479KB) ( 1479 )   Save
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    Gynomonoecy is the mode of sex expression in which female and bisexual flowers occur on the same plants; it is an important step in the evolution of monoecy from hermaphroditism in angiosperms. The sexual system of gynomonoecy is considered to play several important roles, including reducing herbivore damage to pistils, reducing inbreeding depression by favoring out-crossing and pollen-pistil interference, enhancing the flexibility of resource allocation to male and female functions in two flower types, and attracting pollinators. According to the classification of APG III system, gynomonoecy occurs in about 23 families in angiosperms including Lactoridaceae in magnoliids, Araceae and Poaceae in monocots, and Asteraceae, Amaranthaceae, Lamiaceae and other families in eudicots. Gynomonoecy is most common in Asteraceae. Female and bisexual flowers from different gynomonoecious taxa show diversified sex expressions, such as their position in inflorescence, morphs, size and flowering time. These traits are regulated not only by genetic factors, but also by resource availability (e.g., nutrition, light, temperature, and moisture conditions). Because reports on gynomonoecy in China are rare, this paper emphasizes our analysis and summary of the phylogeny of gynomonoecious taxa and their evolution in angiosperm and the relationship between their sex expression and environmental conditions. In addition, five hypotheses on the evolutionary significance of gynomonoecy are introduced and evaluated in this paper. Finally, we discuss prospects for further research in this topical area. Our purpose is to provide a theoretical framework for research on evolutionary patterns and mechanisms of gynomonoecy for angiosperms in China.


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