Data from: Asymmetric sensitivity of ecosystem carbon and water processes in response to precipitation change in a semiarid steppe

1.Semiarid ecosystems play an important role in regulating the dynamics of the global terrestrial CO2 sink. These dynamics are mainly driven by increasing inter-annual precipitation variability. However, how ecosystem carbon processes respond to changes in precipitation is not well understood, due to a lack of substantial experimental evidence that combines increased and decreased precipitation treatments. 2.This study, a 3-year field manipulation experiment with 5 precipitation levels conducted in a semiarid steppe, examined the impacts of increased and decreased precipitation on ecosystem CO2 (GEP: gross ecosystem photosynthesis; ER: ecosystem respiration; NEE: net ecosystem CO2 exchange), water exchange (ET: evapotranspiration), and resource use efficiency (CUE: carbon use efficiency; WUE: water use efficiency). 3.We found that decreased precipitation reduced ecosystem CO2, water exchange and resource use efficiency significantly, while increased precipitation did not cause significant influence on them. That is, they responded more sensitively to decreased precipitation. Soil water availability was the most important driver determining changes in GEP, ER and ET. Changes in NEE, CUE and WUE were predominately regulated by soil temperature. Photosynthesis at leaf and ecosystem levels showed significantly greater sensitivity to changed precipitation than respiration and ET, and therefore determined the trends of net carbon uptake and resource use efficiency. 4.This study highlighted an asymmetric response of ecosystem carbon and water processes to altered precipitation. This is potentially important for improving our understanding of how possible future changes in precipitation will affect the carbon cycle in this ecosystem. Taking this asymmetric response into consideration will inevitably reduce uncertainties in predicting the dynamics of the global carbon cycle.1. 半干旱生态系统（Semiarid ecosystems）在调控全球陆地碳汇动态过程中扮演着至关重要的角色。该动态过程主要受年际降水变率加剧的驱动。然而，由于缺乏同时涵盖降水增加与减少处理的可靠实验证据，学界对于生态系统碳过程如何响应降水变化的机制尚未得到充分阐释。 2. 本研究在半干旱草原（semiarid steppe）开展了为期3年的野外控制实验，设置5个降水梯度，探究了降水增减对生态系统CO₂交换[总生态系统光合作用（gross ecosystem photosynthesis, GEP）、生态系统呼吸（ecosystem respiration, ER）、净生态系统CO₂交换（net ecosystem CO₂ exchange, NEE）]、水分交换（蒸散（evapotranspiration, ET））以及资源利用效率[碳利用效率（carbon use efficiency, CUE）、水分利用效率（water use efficiency, WUE）]的影响。 3. 研究结果表明，降水减少会显著降低生态系统CO₂交换、水分交换与资源利用效率，而降水增加未对上述指标产生显著影响，即生态系统过程对降水减少的响应更为敏感。土壤水分有效性是调控总生态系统光合作用（GEP）、生态系统呼吸（ER）与蒸散（ET）变化的核心驱动因子；而净生态系统CO₂交换（NEE）、碳利用效率（CUE）及水分利用效率（WUE）的变化则主要受土壤温度调控。叶片及生态系统尺度的光合作用对降水变化的响应敏感性显著高于呼吸作用与蒸散，因此决定了净碳吸收与资源利用效率的变化趋势。 4. 本研究揭示了生态系统碳、水过程对降水变化的不对称响应特征，这为深化我们理解未来降水变化如何影响该生态系统碳循环提供了重要参考。将该不对称响应纳入考量，将有效降低全球碳循环动态预测中的不确定性。