Du Yue, Wang Ying-Ping, Su Fanglong, Jiang Jun, Wang Chen, Yu Mengxiao, Yan Junhua
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
CSIRO Oceans and Atmosphere, Aspendale, Vic., Australia.
Glob Chang Biol. 2020 Oct;26(10):6015-6024. doi: 10.1111/gcb.15270. Epub 2020 Jul 29.
Intensification of the Earth's hydrological cycle amplifies the interannual variability of precipitation, which will significantly impact the terrestrial carbon (C) cycle. However, it is still unknown whether previously observed relationship between soil respiration (R ) and precipitation remains applicable under extreme precipitation change. By analyzing the observations from a much larger dataset of field experiments (248 published papers including 151 grassland studies and 97 forest studies) across a wider range of precipitation manipulation than previous studies, we found that the relationship of R response with precipitation change was highly nonlinear or asymmetric, and differed significantly between grasslands and forests, between moderate and extreme precipitation changes. Response of R to precipitation change was negatively asymmetric (concave-down) in grasslands, and double-asymmetric in forests with a positive asymmetry (concave-up) under moderate precipitation changes and a negative asymmetry (concave-down) under extreme precipitation changes. In grasslands, the negative asymmetry in R response was attributed to the higher sensitivities of soil moisture, microbial and root activities to decreased precipitation (DPPT) than to increased precipitation (IPPT). In forests, the positive asymmetry was predominantly driven by the significant increase in microbial respiration under moderate IPPT, while the negative asymmetry was caused by the reductions in root biomass and respiration under extreme DPPT. The different asymmetric responses of R between grasslands and forests will greatly improve our ability to forecast the C cycle consequences of increased precipitation variability. Specifically, the negative asymmetry of R response under extreme precipitation change suggests that the soil C efflux will decrease across grasslands and forests under future precipitation regime with more wet and dry extremes.
地球水文循环的强化加剧了降水的年际变率，这将对陆地碳（C）循环产生重大影响。然而，在极端降水变化的情况下，先前观察到的土壤呼吸（R）与降水之间的关系是否仍然适用尚不清楚。通过分析比以往研究范围更广的降水操纵条件下的大量田间试验数据集（248篇已发表论文，包括151项草地研究和97项森林研究）的观测结果，我们发现R对降水变化的响应关系高度非线性或不对称，并且在草地和森林之间、中等降水变化和极端降水变化之间存在显著差异。在草地中，R对降水变化的响应呈负不对称（下凹），而在森林中呈双不对称，在中等降水变化下呈正不对称（上凹），在极端降水变化下呈负不对称（下凹）。在草地中，R响应的负不对称归因于土壤湿度、微生物和根系活动对降水减少（DPPT）的敏感性高于降水增加（IPPT）。在森林中，正不对称主要由中等IPPT下微生物呼吸的显著增加驱动，而负不对称则由极端DPPT下根系生物量和呼吸的减少引起。草地和森林中R的不同不对称响应将大大提高我们预测降水变率增加对碳循环影响的能力。具体而言，极端降水变化下R响应的负不对称表明，在未来降水格局中干湿极端情况增多的情况下，草地和森林的土壤碳通量将减少。
