季节非对称性增温对高寒草甸植物与微生物养分关系的影响

Warming in winter on the Qinghai-Tibetan Plateau is over-proportionally affected by climate warming. The observed warming over the past decades is greater in non-growing season than in growing season. An increased frequency of soil freeze–thaw cycles at the winter-spring transition induced by warming during non-growing season may have great impacts on nutrient cycles in alpine ecosystems. However, studies on warming mostly focused on year-round warming effects, and ignored the facts of asymmetric warming. To better understand the response and underlying mechanism of alpine ecosystems to climate change, studies on the partitioning of nitrogen (N) between plants and soil microbes at the winter-spring transition and carry-over effects are needed. Based on field asymmetric warming experiment, we will dynamically monitor the N decoupling process during soil freezing-thaw cycles using in-suit incubation and 15N isotope tracer techniques in an alpine meadow. We will also investigate the carry-over effects on nutrient supply and the competition for N between plants and soil microbes during growing season. The results of this study are expected to provide insights into how nutrient cycling of alpine ecosystem responds to future climate change and its mechanism on the Qinghai-Tibetan Plateau.

青藏高原气候变暖呈现非生长季升温幅度高于生长季的季节非对称性升温趋势，导致冬春转换时期冻融循环提前、频率增加，将对受氮限制的高寒生态系统的养分循环产生重要影响。但当前的增温研究集中于全年增温的影响，忽略了季节非对称性升温的事实。为了阐明高寒生态系统对气候变化的响应及其机制，亟待研究季节非对称性升温对冻融时期植物与土壤微生物养分利用关系及其后续效应。本项目基于植物-微生物响应与作用的理论框架，在西藏当雄草原站季节非对称性增温试验平台，采用原位培养和15N同位素标记技术,动态监测季节非对称性升温对冻融时期微生物养分释放及植物养分吸收过程的影响，探讨微生物介导的资源供应变化如何影响生长季植物-微生物养分关系。项目结果有望为高寒生态系统养分循环对未来气候变化的响应提供机理解释。

气候变暖是目前面临的重要环境问题。研究表明，目前的变暖趋势呈现非生长季升温显著高于生长季的季节非对称特征，青藏高原的变暖趋势更是如此。非生长季升温幅度增大会导致冻融循环提前、频率增加，将对受氮限制的高寒生态系统产生重要影响。但当前的增温研究主要集中于全年增温，忽略了季节非对称性的事实。为了准确预测高寒生态系统对气候变化的响应及其机制，亟待研究季节非对称性升温对高寒生态系统养分循环及其他生态过程的影响。本项目基于植物-土壤微生物响应与作用的理论框架，依托于我们在青藏高原设置的长期季节非对称性增温平台，系统研究了冻融交替时期植物与微生物的养分关系以及对生态系统养分动态的影响，并对由此引起的延滞效应。研究发现，冬季增温处理导致冻融交替活动提前，从而导致植物与微生物关系在养分释放与吸收的时间动态上出现解耦，进而导致生态系统氮流失的增加。土壤养分含量的变化会产生延滞效应，影响随后生长季各个生态过程。冬季增温引起的养分含量变化会影响植物养分利用效率与策略：增温导致植物叶片氮磷回收效率提高，说明植物受养分的限制增强。养分限制模式的改变会影响生态系统生产，引起生产力分配模式的改变和碳排放的降低等一系列延滞效应的出现。从长期来看，这种延滞效应会影响高寒生态系统整个生长季节的群落结构和稳定性。因此，本项目的研究结果对于阐明高寒生态系统生物地球化学循环的季节变化过程至关重要，对揭示生态过程对未来气候变化的响应具有重要意义。