Abstract：
Rewilding abandoned farmlands provides a nature-based climate solution via carbon (C) offsetting; however, the C-cycle-climate feedback in such restored ecosystems is poorly understood. Therefore, we conducted a 2-year field experiment in Loess Plateau, China, to determine the impacts of warming (∼1.4 °C) and altered precipitation (±25 %, ±50 %, and ambient), alone or in concert on soil C pools and associated C fluxes. Experimental warming significantly enhanced soil respiration without affecting the ecosystem net C uptake and soil C storage; these variables tended to increase along the manipulated precipitation gradient. Their interactions increased ecosystem net C uptake (synergism) but decreased soil respiration and soil C accumulation (antagonism) compared with a single warming or altered precipitation. Additionally, most variables related to the C cycle tended to be more responsive to increased precipitation, but the ecosystem net C uptake responded intensely to warming and decreased precipitation. Overall, ecosystem net C uptake and soil C storage increased by 94.4 % and 8.2 %, respectively, under the warmer-wetter scenario; however, phosphorus deficiency restricted soil C accumulation under these climatic conditions. By contrast, ecosystem net C uptake and soil C storage decreased by 56.6 % and 13.6 %, respectively, when exposed to the warmer-drier climate, intensifying its tendency toward a C source. Therefore, the C sink function of semiarid abandoned farmland was unsustainable. Our findings emphasize the need for management of post-abandonment regeneration to sustain ecosystem C sequestration in the context of climate change, aiding policymakers in the development of C-neutral routes in abandoned regions.
摘要：
重新绿化废弃的农田通过碳（C）抵消提供了基于自然的气候解决方案；但是，在这种恢复的生态系统中，人们对C循环-气候反馈知之甚少。因此,我们在黄土高原进行了为期两年的田间试验，中国,为了确定变暖(~1.4℃)和降水变化(±25%，±50%,和环境)，单独或一致地在土壤碳库和相关的碳通量上。实验变暖显着增强了土壤呼吸，而不影响生态系统的净碳吸收和土壤碳储量；这些变量倾向于沿操纵的降水梯度增加。与单一变暖或降水变化相比，它们的相互作用增加了生态系统的净碳吸收（协同作用），但降低了土壤呼吸和土壤碳积累（拮抗作用）。此外,与C循环相关的大多数变量倾向于对增加的降水更敏感，但是生态系统的净碳吸收对变暖和降水减少反应强烈。总的来说,生态系统净碳吸收和土壤碳储量分别增加了94.4%和8.2%，分别,在温暖潮湿的情况下；然而，在这些气候条件下，磷缺乏限制了土壤碳的积累。相比之下,生态系统净碳吸收和土壤碳储量分别下降了56.6%和13.6%，分别,当暴露在温暖干燥的气候中时，加强其朝向C源的趋势。因此,半干旱废弃农田的C汇功能是不可持续的。我们的研究结果强调，在气候变化的背景下，需要对废弃后的再生进行管理，以维持生态系统C的隔离。协助政策制定者在废弃地区开发C中性路线。
