Threshold response of ecosystem water use efficiency to soil water in an alpine meadow

Tingting Li; Dashuan Tian; Yicheng He; Ruiyang Zhang; Jinsong Wang; Furong Wang; Shuli Niu

doi:10.1016/j.scitotenv.2023.168345

Threshold response of ecosystem water use efficiency to soil water in an alpine meadow

Sci Total Environ. 2024 Jan 15:908:168345. doi: 10.1016/j.scitotenv.2023.168345. Epub 2023 Nov 5.

Authors

Tingting Li¹, Dashuan Tian², Yicheng He³, Ruiyang Zhang⁴, Jinsong Wang⁴, Furong Wang¹, Shuli Niu¹

Affiliations

¹ Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
² Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: tiands@igsnrr.ac.cn.
³ College of Grassland Science and Technology, China Agricultural University, Beijing 100193, China.
⁴ Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China.

PMID: 37935265
DOI: 10.1016/j.scitotenv.2023.168345

Abstract

Ecosystem water use efficiency (WUE) is a coupled index of carbon (gross ecosystem productivity, GEP) and water fluxes (transpiration, Tr or evapotranspiration, ET), reflecting how ecosystem uses water efficiently to increase its carbon uptake. Though ecosystem WUE is generally considered to decrease with increasing precipitation levels, it remains elusive whether and how it nonlinearly responds to extreme water changes. Here, we performed a 5-year precipitation halving experiment in an alpine meadow, combined with extremely interannual precipitation fluctuations, to create a large range of soil water variations. Our results showed that WUE_Tr and WUE_ET consistently showed a quadratic pattern in response to soil water. Such quadratic patterns were steadily held at different stages of growing seasons, with minor changes in the optimal water thresholds (25.0-28.4 %). Below the water threshold, more soil water stimulated GEP but reduced Tr and ET by lowering soil temperature, resulting in a positive response of ecosystem WUE to soil water. Above the threshold, soil water stimulated GEP less than Tr (ET), leading to a negative response of ecosystem WUE to soil water. However, biological processes, including plant cover and belowground biomass as well as vertical root biomass distribution, had less effect on ecosystem WUE. Overall, this work is among the first to reveal the nonlinearity and optimal water thresholds of ecosystem WUE across a broad range of soil water, suggesting that future extreme precipitation events will more frequently surpass the water threshold and differently change the coupling relationships of carbon and water fluxes in alpine grasslands.

Keywords: Alpine meadow; Ecosystem water use efficiency; Evapotranspiration; Gross ecosystem productivity; Transpiration; Water threshold.