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Atmospheric water vapor and soil moisture jointly determine the spatiotemporal variations of CO2 fluxes and evapotranspiration across the Qinghai-Tibetan Plateau grasslands
Li, Hongqin; Wang, Chunyu; Zhang, Fawei; He, Yongtao; Shi, Peili; Guo, Xiaowei; Wang, Junbang; Zhang, Leiming; Li, Yingnian; Cao, Guangmin; Zhou, Huakun
2021
Source PublicationSCIENCE OF THE TOTAL ENVIRONMENT
Volume791
AbstractAlpine grasslands play important functions in mitigating climate change and regulating water resources. However, the spatiotemporal variability of their carbon and water budgets remains unquantified. Here, 47 site-year observations of CO2 and water vapor fluxes (ET) are analyzed at sites situated along a hydrothermal gradient across the Qinghai-Tibetan Plateau, including an alpine wetland (wettest), an alpine shrub (coldest), an alpine meadow, an alpine meadow-steppe, and an alpine steppe (driest and warmest). The results show that the benchmarks for annual net ecosystem exchange (NEE) are -79.3, -77.8, -66.7, 20.2, and 100.9 g C m(-2) year(-1) at the meadow, shrub, meadow-steppe, steppe, and wetland, respectively. The peak daily NEE normalized by peak leaf area index converges to 0.93 g C m(-2) d(-1) at the 5 sites. Except in the wetland (722.8 mm), the benchmarks of annual ET fluctuate from 511.0 mm in the steppe to 589.2 mm in the meadow. Boosted regression trees-based analysis suggests that the enhanced vegetation index (EVI) and net radiation (Rn) determine the variations of growing season monthly CO2 fluxes and ET, respectively, although the effect is to some extent site-specific. Inter-annual variability in NEE, ecosystem respiration (RES), and ET are tightly (R-2 > 0.60) related to the inter growing season NEE, RES, and ET, respectively. Both annual RES and annual NEE are significantly constrained by annual gross primary productivity (GPP), with 85% of the per-unit GPP contributing to RES (R-2 = 0.84) and 15% to NEE (R-2 = 0.12). Annual GPP significantly correlates with annual ET alone at the drier sites of the meadow-steppe and the steppe, suggesting the coupling of carbon and water is moisture-dependent in alpine grasslands. Over half of the inter-annual spatial variability in GPP, RES, NEE, and ET is explained by EVI, atmospheric water vapor, topsoil water content, and bulk surface resistance (rs), respectively. Because the spatial variations of EVI and rs are strongly regulated by atmospheric water vapor (R-2 = 0.48) and topsoil water content (R-2 = 0.54), respectively, we conclude that atmospheric water vapor and topsoil water content, rather than the expected air/soil temperatures, drive the spatiotemporal variations in CO2 fluxes and ET across temperature-limited grasslands. These findings are critical for improving predictions of the carbon sequestration and water holding capacity of alpine grasslands. (C) 2021 Published by Elsevier B.V.
KeywordCO2 and water vapor exchanges Boosted regression trees Enhanced vegetation index Net radiation Bulk surface resistance Alpine grasslands
Document Type期刊论文
Identifierhttp://210.75.249.4/handle/363003/60691
Collection中国科学院西北高原生物研究所
Recommended Citation
GB/T 7714
Li, Hongqin,Wang, Chunyu,Zhang, Fawei,et al. Atmospheric water vapor and soil moisture jointly determine the spatiotemporal variations of CO2 fluxes and evapotranspiration across the Qinghai-Tibetan Plateau grasslands[J]. SCIENCE OF THE TOTAL ENVIRONMENT,2021,791.
APA Li, Hongqin.,Wang, Chunyu.,Zhang, Fawei.,He, Yongtao.,Shi, Peili.,...&Zhou, Huakun.(2021).Atmospheric water vapor and soil moisture jointly determine the spatiotemporal variations of CO2 fluxes and evapotranspiration across the Qinghai-Tibetan Plateau grasslands.SCIENCE OF THE TOTAL ENVIRONMENT,791.
MLA Li, Hongqin,et al."Atmospheric water vapor and soil moisture jointly determine the spatiotemporal variations of CO2 fluxes and evapotranspiration across the Qinghai-Tibetan Plateau grasslands".SCIENCE OF THE TOTAL ENVIRONMENT 791(2021).
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