Abstract
The response mechanism of ecosystem respiration (Re) and soil respiration (Rs) to different water conditions is of great significance for understanding the carbon cycle under future changes in the precipitation patterns. We used seven precipitation treatments to investigate the effects of precipitation on Re and Rs on a typical alpine steppe in Northern Tibet. Precipitation was captured and relocated to simulate the precipitation rates of −25, −50, −75, 0 (CK), +25, +50, and +75%. The soil moisture was influenced by all the precipitation treatments. There was a positive linear relationship between the soil moisture and Re, Rs in the study area during the experiment (July–October). Soil volumetric water content (VWC), absolute water content (AWC), soil temperature (ST), aboveground biomass (AGB), bulk density, soil total nitrogen (TN), and alkaline hydrolysis nitrogen (AHN) were the predictors of Re and Rs. The multiple linear regression analysis showed that ST and AWC could explain 90.6% of Rs, and ST, AWC, and AHN could explain 89.4% of Re. Ecosystem respiration was more sensitive to the increased precipitation (+29.5%) whereas Rs was more sensitive to the decreased precipitation (−23.8%). An appropriate increase in water (+25 and +50%) could improve the Re and Rs, but a greater increase (+75%) would not have a significant effect; it could have an effect even lower than those of the first two. Our study highlights the importance of increased precipitation and the disadvantage of decreased precipitation on Re and Rs in an arid region. The precipitation changes will lead to significant changes in the soil properties and AGB, and affect Re and Rs, to change the climate of the alpine steppe in Northern Tibet in the future. These findings contribute to our understanding of the regional patterns of environmental C exchange and soil C flux under the climate change scenarios and highlight the importance of water availability to the regulating ecosystem processes in semi-arid steppe ecosystems. In view of these findings, we urge future researchers to focus on manipulating the precipitation over longer time scales, seasonality, and incorporating more environmental factors to improve our ability to predict and model Re and Rs and feedback from climate change.
Highlights
Ecosystem respiration (Re), one of the major fluxes in the terrestrial ecosystems and the atmospheric carbon cycle, is the main way that carbon is removed from an ecosystem (Johnston et al, 2021)
The Rs was significantly higher in W1 and CK than in D2, and there was no significant difference between D1 and D2 (Figures 2A,B)
Our research showed that the increased precipitation treatments increased Re, Rs, and aboveground biomass (AGB)
Summary
Ecosystem respiration (Re), one of the major fluxes in the terrestrial ecosystems and the atmospheric carbon cycle, is the main way that carbon is removed from an ecosystem (Johnston et al, 2021). Many studies have shown that air temperature, relative air humidity, soil temperature (ST), soil moisture content, plant aboveground biomass (AGB), aboveground respiration, and groundwater level affect the monthly total change of Re and seasonal dynamics; different regions exhibited different responses (Huang et al, 2009; Fang et al, 2012). Soil contains approximately two times as much carbon as that stored in the atmosphere; even small soil carbon flux changes can have a significant impact on the global ecosystem carbon cycle (Lee et al, 2017). The precipitation changes affect Rs mainly through the changes in the ecosystem processes, such as plant growth (Yan et al, 2011; Zhou et al, 2016), soil microbial activity (Zhao et al, 2016a; Ren et al, 2018), and temperature sensitivity (Liu et al, 2016). It is imperative to improve our mechanistic understanding of Rs responses to the precipitation and soil moisture changes
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