IF: 1.780
5-year IF: 2.674
Editors-in-Chief
Wen-Hao Zhang
Bernhard Schmid
CN 10-1172/Q
ISSN 1752-9921(print)
ISSN 1752-993X(online)
  • Volume 15,Issue 5
    01 September 2022
    (In Progress)
      Editorial
      Zhongmin Hu, Shipin Chen and Yanbin Hao
      2022, 15 (5): 879-881.
      Abstract ( 4 )   PDF   Save

      Carbon and water fluxes are the core ecosystem processes, which is linked to diverse ecosystem services (Lian et al. 2021). Therefore, clarifying the variations and controls of ecosystem carbon and water fluxes is an effective approach to clarifying how ecosystem respond to global change in EVAs (Baldocchi 2020). As the only technique can directly measure the carbon, water and energy fluxes between vegetation and atmosphere, eddy covariance technique has been considered as a standard method for flux observations (Chen et al. 2020). By integrating long-term, eddy covariance measurements over time and space, researches are able to assess ecosystem metabolism at different time scales (hours to decades) (Forzieri et al. 2020; Han et al. 2020; Jung et al. 2017). Eddy covariance measurements also produce information on how ecosystem respond to the changes in climate, which is useful for assessing ecosystem carbon sequestration (Hu et al. 2018), water and energy balance (Forzieri et al. 2020), resource use efficiency (Liu et al. 2019) and ecosystem feedback to climate change (Huang et al. 2019; Piao et al. 2020; Yue et al. 2020). Long-term flux measurements are also vital for detecting the responses of ecosystem functions to extreme events, optimizing and validating models on regional and global scales (Baldocchi 2020). Combining with remote sensing and ecosystem modeling techniques, scientists can upscale and evaluate the functional relations between carbon and water fluxes with environmental variables at high resolution and across diverse spatial/temporal scales (Niu et al. 2017; Xia et al. 2020).

      With the continual efforts from scientists in the past two decades, diverse observations facilities, especially eddy flux towers have been established to monitor ecosystem functioning in EVAs in China (Yu et al., 2006). With the data accumulated based on these observations, enhancing our knowledge of carbon and water fluxes in ecologically vulnerable areas in China become feasible. The authors of this special issue share their findings and insights on how ecosystem carbon and water fluxes at different spatial and temporal scales in EVAs in China. For example, on ecosystem carbon flux, in the water-limited grasslands in Inner Mongolia, You et al. (2022) found that leaf area index directly and soil water content indirectly affected photosynthetic parameters at the canopy scale. In a Tibetan alpine meadow ecosystem, Xu et al. (2022a) revealed that biotic factors, rather than climatic factors, dominated the interannual variations in carbon fluxes. In saline–alkaline grassland, Diao et al. (2022) found that nitrogen deposition simulated soil respiration and the effect was nitrogen compounds dependent from a 3-year field experiment. In the Bayinbuluk alpine wetland, Yao et al. (2022) used an automatic chamber system d reported that the seasonal variations of ecosystem respiration were controlled by soil temperature and water content. On ecosystem water flux, Xu et al. (2022b) reported that variations of ecosystem evapotranspiration (ET) were dominated by net radiation and air temperature and behaved energy limited in wet peak season. However, variations of ET were regulated by canopy stomatal conductance and leaf area index and were water limited in dry seasons. In a desert steppe, Du et al. (2022) found that gross primary production responded more quickly to the plant water stress than ET, which decreased water use efficiency. The large-scale afforestation should fully consider the cost of water consumption. On extreme climate, Zhang et al. (2022) conducted the Fisher discriminant model, involving soil water content and saturated vapor pressure deficit, and successfully detect drought occurrence. The publications of this special issue will largely enrich our understanding the functioning of ecosystems in vulnerable areas in China.

      We are grateful to the editorial team of Journal of Plant Ecology, particularly to Wen-Hao Zhang, Bernhard Schmid and Li-Juan Liu, for giving us the opportunity to organize this special issue. The publication of this special issue would not have been possible without their support. We sincerely hope that this special issue will advance our mechanistic understanding of carbon and water functions in vulnerable ecosystems in China.

      Research Articles
      Mingjie Xu, Yi Sun, Tao Zhang, Yangjian Zhang, Juntao Zhu, Yongtao He, Liwei Wang and Guirui Yu
      2022, 15 (5): 882-896.
      Abstract ( 3 )   PDF   Save

      The alpine meadow ecosystem in Tibet is fragile and sensitive, and its carbon sink function with respect to climate change has become a matter of widespread concern. Therefore, this study aims to clarify the inter-annual variations (IAVs) in the carbon fluxes in an alpine meadow and to further quantify the contributions of the driving factors to the IAVs. Based on 7 years of flux data (2012–2018) and the corresponding climatic and biotic data, a set of look-up tables was used to separate and quantify the IAV sources. Furthermore, linear perturbation analyses were employed to quantify the contributions of each key factor. During 2012–2018, the net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Re) of this alpine meadow were 3.31 ± 26.90, 210.18 ± 48.35 and 206.88 ± 28.45 g C m−2 y−1, respectively, which indicated relatively large IAVs. When the contributions of climatic and biotic effects were distinguished and quantified, the dominant effects of biotic factors emerged. Additionally, negative interactions between climatic and biotic effects were detected. Among the climatic factors, only soil water content contributed relatively more to the IAVs and played a role in regulating the interactions between climatic and biotic effects. These results suggest that biotic effects must be carefully considered to reduce the uncertainties associated with future carbon flux estimates.

      Huajie Diao, Xiaopeng Chen, Ge Wang, Qiushi Ning, Shuya Hu, Wei Sun, Kuanhu Dong and Changhui Wang
      2022, 15 (5): 897-910.
      Abstract ( 2 )   PDF   Save

      The increase in atmospheric nitrogen (N) deposition has profound effects on soil respiration (SR). However, the responses of SR to the addition of different N compounds, particularly in saline–alkaline grasslands remain unclear. A 3-year controlled field experiment was conducted to investigate the responses of SR to different N compounds (NH4NO3, (NH4)2SO4 and NH4HCO3) during the growing seasons in a saline–alkaline grassland located in the agro-pastoral ecotone of northern China. Our results demonstrated that SR showed a bimodal pattern and a significant interannual difference that was regulated by air or soil temperature and precipitation. Nitrogen addition had a significant effect on SR, and the effect of N addition on SR varied yearly, which was related to seasonal precipitation. The mean SR across 3 years (2017–2019) was increased by 19.9%, 13.0% and 16.6% with the addition of NH4NO3, (NH4)2SO4 and NH4HCO3, respectively. The highest effect of NH4NO3 addition on SR across 3 years was ascribed to the highest aboveground net primary production, belowground net primary production (BNPP) and soil NO3 concentrations. SR (C loss) was significantly increased while plant productivity (C input) did not significantly change under NH4HCO3 addition, indicating a decrease in C sequestration. In addition, BNPP was the main direct factor influencing SR in this saline–alkaline grassland, and soil salinization (e.g. soil base cations and pH) indirectly affected SR through soil microorganisms. Notably, NH4NO3 addition overestimated the response of SR to N addition, and different N compounds should be considered, especially in saline–alkaline grassland.

      Tao Zhang, Ximeng Ji, Yuanyuan Tang, Mingjie Xu, Yangjian Zhang, Guang Zhao, Ning Chen, Juntao Zhu and Yongtao He
      2022, 15 (5): 911-920.
      Abstract ( 1 )   PDF   Save

      Fisher discriminant analysis can comprehensively take multiple factors into consideration and effectively conduct separations between two classes. If it can be used to detect the occurrences of drought, drought can be detected more effectively and accurately. Based on 9-year carbon flux and corresponding meteorological data, soil water content (SWC) and vapor pressure deficit (VPD) were selected as the discriminant factors. Drought occurrences were detected by applying the Fisher discriminant analysis method in an alpine ecosystem in Tibet. Fisher discriminant analysis was successfully applied to detect drought occurrence in an alpine meadow ecosystem. The soil water deficit and atmospheric water deficit were comprehensively taken into consideration. Consequently, this method could detect the onset and end date of droughts more accurately and reasonably. Based on the characteristics of drought and non-drought samples, the discriminant equation was constructed as y = 24.46SWC − 4.60VPD. When y > 1, the days were distributed above the critical line. In addition, when y was greater than one for more than 10 days, it was labeled as one drought event. If the interval between two drought processes was less than 2 days, it was considered one drought event. With increasing the study period and continued accumulation of observation data, the discriminant equation could be further optimized in the future, resulting in more accurate drought detection.

      Mingjie Xu, Tingting An, Zhoutao Zheng, Tao Zhang, Yangjian Zhang and Guirui Yu
      2022, 15 (5): 921-932.
      Abstract ( 1 )   PDF   Save

      The Tibetan Plateau is generally referred to as the Chinese water tower, and evapotranspiration (ET) affects the water budget and stability of alpine meadows on the Tibetan Plateau. However, its variability and controlling mechanisms have not been well documented under the drier conditions induced by global warming. Therefore, this study aimed to clarify whether meteorological or biological factors primarily affected the variability in ET under contrasting water conditions in the alpine meadow ecosystem on the Tibetan Plateau. Based on 6-year (2013–2018) eddy covariance observations and the corresponding meteorological and biological data, linear perturbation analyses were employed to isolate the contributions of meteorological and biological factors to the variability in evapotranspiration (δET). The results showed that δET was mainly driven by meteorological factors in wet peak seasons (July and August), and was dominated by net radiation (Rn) and air temperature (Ta), indicating that the inadequate available energy is the factor limiting ET. However, the dominant factors affecting δET shifted from meteorological to biological in dry peak seasons when the canopy stomatal conductance (gs) and leaf area index were dominant. At this point, the ecosystem was limited by the water conditions. These results provide empirical insights into how meteorological and biological factors regulate variability in ET under contrasting water conditions. These findings can further improve our understanding of water cycle processes and can help effectively manage water resources in alpine meadow ecosystems under future climate change conditions.

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