Collaborative Research: Aboveground and Belowground Community Responses to Climate Changes in Arctic Tundra

虽然现有的观测结果表明，北极植物群落在物种组成、净初级生产力（NPP）和生物量方面经历了巨大的变化，以响应气候变暖和随后土壤养分矿化的增加，但目前用于预测北极冻土带碳(C)和氮(N)循环的模型缺乏更高营养水平的考虑，因此缺少可能具有相当大影响的机制。提供资金同时测量植物、土壤无脊椎动物和微生物（生物量和多样性）对土壤养分增加的反应，以测试有关这些变化的生态学理论，并了解营养水平之间的反馈。拟议的工作解决了我们是否正在目睹生态系统组成部分的简单增加和微妙变化，或者生态系统的根本变化，这些变化有可能改变当前生物群，碳和氮的平衡。理论认为，当NPP增加时，额外的营养水平应该进入系统，因为现在有足够的能量来维持它们。这些变化在NPP较低的系统（如北极苔原）将更为显著，因为动态不是线性的。该研究将研究土壤群落和养分循环如何对植物生长的变化做出反应，以及如何在NPP、干燥健康和潮湿酸性草堆苔原两种常见的北极生态系统之间比较这些反应。它将利用位于阿拉斯加图里克湖的北极LTER现有实验地块，在长期营养富集的地块尺度上测试这些假设，并将建立新的小规模营养修正实验，在这些实验中，将进行更局部和更频繁的植物和土壤采样，以捕获更适合土壤生物的时空尺度。理论和经验为基础的模型将被用来帮助分析和解释。

While existing observations suggest that arctic plant communities undergo dramatic changes in species composition, net primary productivity (NPP), and biomass in response to climate warming and subsequent increased soil nutrient mineralization, current models used to predict carbon (C) and nitrogen (N) cycling in arctic tundra are lacking inclusion of higher trophic levels and, thus, are missing mechanisms that may be having considerable effects. Funds are proided to concurrently measure plants, soil invertebrates and microbes (biomass and diversity) as they respond to increased soil nutrients to test ecological theory regarding such changes and understand feedbacks among trophic levels. The proposed work addresses whether we are witnessing simpleincreases and subtle shifts in the ecosystem components or fundamental changes in the ecosystem that have the potential to alter the current balance of biota, carbon and nitrogen.Theory suggests that when NPP increases, additional trophic levels should enter the system because there is now enough energy to sustain them. These changes will be more dramatic in lower NPP systems, such as arctic tundra, because the dynamics are not linear. The study will examine how soil communities and nutrient cycling respond to changes in plant growth and how these responses compare between two common arctic ecosystems that differ in NPP, dry heath and moist acidic tussock tundra. It will use existing experimental plots of the Arctic LTER at Toolik Lake, Alaska to test these hypotheses at the plot scale under long-term nutrient enrichment and will establish new smaller-scale nutrient amendment experiments on which more localized and frequent plant and soil sampling will occur to capture a temporal and spatial scale more appropriate for soil organisms. Theoretical and empirically-based models will be used to aid in the analysis and interpretation.