Carbon and water fluxes and their coupling in an alpine meadow ecosystem on the northeastern Tibetan Plateau
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ORIGINAL PAPER
Carbon and water fluxes and their coupling in an alpine meadow ecosystem on the northeastern Tibetan Plateau Yuyang Wang 1,2
&
Yaoming Ma 1,2,3 & Haixia Li 1 & Ling Yuan 1,2
Received: 9 September 2019 / Accepted: 12 June 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Alpine meadow is one of the most widely distributed vegetation types on the Tibetan Plateau—the Earth’s Third Pole. Characterizing the carbon and water vapor fluxes in alpine meadow ecosystems is of particular importance for elucidating the mechanisms underlying the carbon budget and water cycle in high-altitude areas, especially under changing climatic conditions. Thus, the quantitative relationships between carbon and water fluxes and environmental drivers were examined based on a continuous eddy covariance (EC) dataset from 2013 to 2015 over the alpine Kobresia meadow on the northeastern Tibetan Plateau. The results show that (1) the net ecosystem CO2 exchange (NEE) was − 152.89 g C m−2 year−1, − 197.69 g C m−2 year−1, and − 160.09 g C m−2 year−1 from 2013 to 2015, respectively, suggesting that this alpine meadow ecosystem is a strong and consistent carbon sink. (2) Both the multiple stepwise regression analysis (MSRA) and the structural equation model (SEM) analysis confirmed the dominant role of Ts in controlling the carbon flux and that of Rn in controlling the water vapor flux. (3) The inherent water use efficiency (IWUE = GPP×VPD/ET) and underlying water use efficiency (uWUE = GPP×VPD0.5/ET), which incorporates the vapor pressure deficit (VPD) effect, better described the carbon-water coupling characteristics at daily and hourly scales than did the traditional water use efficiency (WUE = GPP/ET). These findings highlight the dominant climatic factors controlling CO2 and water vapor exchanges and contribute to our knowledge of the land surface-atmosphere exchange in alpine meadows on the Tibetan Plateau.
1 Introduction Environmental factors exert enormous influence on ecosystem carbon and water vapor fluxes, especially in alpine grassland ecosystems, which are highly susceptible to changing climate (Li et al. 2006; Li et al. 2019; Saito et al. 2009). Knowledge of the key factors affecting ecosystem CO2 and water vapor exchanges is crucial because these processes
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00704-020-03303-3) contains supplementary material, which is available to authorized users. * Yaoming Ma [email protected] 1
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China
strongly associated with regional carbon and water balance (Green et al. 2019; Jia et al. 2016). Thus, an increasing number of studies have focused on the environmental factors
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