Global Change and the Carbon Balance of Arctic Ecosystems: The Importance of Carbon/Nutrient Interactions

这项研究的主题是碳/营养相互作用对陆地生态系统碳循环过程和总体碳收支的制约作用。特别关注的是阿拉斯加北部从旱地到潮湿低地的三个不同冻土带生态系统中的碳/养分相互作用。这项研究是在全球变暖的背景下进行的，将预测的全球气温上升视为生态系统层面上碳/养分相互作用的实验。其核心思想是，北极生态系统的初级生产力受到严重的养分限制，因此其对较高温度的反应能力受到养分供应的限制。另一方面，土壤呼吸更直接地受到土壤温度的限制，土壤有机质中养分的矿化也是如此。因此，与养分矿化增加相关的植物碳收益必须与因土壤呼吸增加而造成的土壤碳损失相平衡。为了了解生态系统层面对碳平衡的控制，人们需要了解对植物碳/养分比率和土壤碳呼吸与N、P矿化比率的控制。提出了包括过程研究、全生态系统实验和模拟建模的研究方案。这些过程研究旨在提高对陆地生态系统有机质循环关键点上的C/N/P相互作用的理解，特别是对土壤呼吸和N、P矿化的平衡。全生态系统试验的重点是确定主要有机质通量的C：N：P比值变化与有机质库之间的相关性。建模工作旨在帮助解释整个生态系统中的这些相关变化，确定因果关系，并澄清对观察到的C：N：P比率变化范围的限制。

The Subject of this research is the role of carbon/nutrient interactions as constraints on carbon cycling processes and overall carbon budgets of terrestrial ecosystems. The specific focus is on carbon/nutrient interactions in three contrasting tundra ecosystems along a continuum from dry uplands to wet lowlands in northern Alaska. The research is placed in the context of global warming, viewing the predicted global temperature increase as an experiment in carbon/nutrient interactions at the ecosystem level. The central idea is that primary production of arctic ecosystem is strongly nutrient-limited, and thus its ability to respond to higher temperatures is constrained by nutrient supply. Soil respiration, on the other hand, is more directly limited by low soil temperature, as is the mineralization of nutrients in soil organic matter. Plant carbon gains associated with increased nutrient mineralization must thus be balanced against soil carbon losses due to increased soil respiration. To understand controls on carbon balance at the ecosystem level, one needs to understand controls on plant carbon/nutrient ratios and the ratio of soil carbon respiration to N and P mineralization. A program of research is proposed that includes process studies, whole- ecosystem experiments, and simulation modeling. The process studies are designed to improve understanding of C/N/P interactions at key points in the cycle of organic matter in terrestrial ecosystems, with a particular focus on the balance of soil respiration and N and P mineralization. The whole- ecosystem experiments are focused on determining correlations between changes in the C:N:P ratios of the major organic matter fluxes and organic matter pools. The modeling efforts are designed to help explain these correlated changes in whole ecosystems, to identify cause-effect relationships, and to clarify constraints on the observed range of variation in C:N:P ratios.