Differential responses of CO2 and latent heat fluxes to climatic anomalies on two alpine grasslands on the northeastern Qinghai-Tibetan Plateau

Hongqin Li; Fawei Zhang; Jiexia Li; Xiaowei Guo; Huakun Zhou; Yingnian Li

doi:10.1016/j.scitotenv.2023.165863

Differential responses of CO₂ and latent heat fluxes to climatic anomalies on two alpine grasslands on the northeastern Qinghai-Tibetan Plateau

Sci Total Environ. 2023 Nov 20:900:165863. doi: 10.1016/j.scitotenv.2023.165863. Epub 2023 Jul 28.

Authors

Hongqin Li¹, Fawei Zhang², Jiexia Li³, Xiaowei Guo³, Huakun Zhou³, Yingnian Li³

Affiliations

¹ College of Life Sciences, Luoyang Normal University, Luoyang, Henan 471934, China; Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810008, China; Qinghai Provincial Key Laboratory of Restoration Ecology in Cold Region, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810008, China.
² Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810008, China; Qinghai Provincial Key Laboratory of Restoration Ecology in Cold Region, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810008, China. Electronic address: mywing963@126.com.
³ Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810008, China; Qinghai Provincial Key Laboratory of Restoration Ecology in Cold Region, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810008, China.

PMID: 37516184
DOI: 10.1016/j.scitotenv.2023.165863

Abstract

Discrete extreme heat events, deluges, and droughts will become more frequent and disproportionately affect the processes and functions of grassland ecosystems. Here, we compared the responses of CO₂ and heat fluxes to natural extreme events in 2016 in a lower alpine meadow and neighboring upper shrubland on the northeastern Qinghai-Tibetan Plateau. Unlike insensitive sensible heat flux, latent heat flux (LE) increased by 21.8 % in the meadow and by 56.4 % in the shrubland during a dry period and subsequent compound hot-dry period in August. Changes (Δ, data for 2016 minus the corresponding means from other years) in the heat flux at both sites were determined by changes in solar radiation (ΔSwin), as sufficient soil moisture was available. ΔLE was more sensitive to ΔSwin in the open-canopy shrubland, reflecting its greater capacity for evaporative cooling to buffer climate anomalies. CO₂ fluxes responded weakly to extreme wet or dry events but strongly when those events were accompanied by exceptional heat. During single or compound hot events, the mean changes in total ecosystem respiration (ΔTER) increased by about 30 % in both grasslands, although ΔTER was more sensitive to changes in the topsoil temperature in the more productive meadow than in the shrubland. The mean changes in gross primary productivity (ΔGPP) fluctuated by <10 % in the warmer meadow but increased by 29.3 % in the cooler shrubland relative to the respective baseline, probably because of the differences in canopy structure and root depth and the consequent high-temperature stress on vegetation photosynthesis. The changes in net ecosystem CO₂ exchange (ΔNEE) were significantly related to ΔTER in the meadow and increased by 55.8 %, whereas ΔNEE was controlled mainly by ΔGPP in the shrubland and decreased by 22.4 %. Overall, both alpine grasslands were resistant to rainfall anomalies but susceptible to exceptional warmth, with the differential responses being ascribed to canopy structure and root depth. Our results provide helpful insights based on which the carbon sequestration and water-holding functions of alpine grasslands during future climate change can be predicted.

Keywords: Alpine grasslands; CO(2) flux; Climatic anomalies; Exceptional warmth; Heat flux; Rainfall change.