Global Change and the Carbon Balance of Arctic Ecosystems: The Importance of Carbon-Nutrient Interactions in Soils

9615563陆地碳循环中的纳德尔霍夫变化往往受到碳与其他元素，特别是氮和磷之间的相互作用的严格制约。本研究的目的是提高对土壤中碳/养分相互作用如何影响北极冻土带生态系统对全球环境变化的响应的理解。这项研究的中心问题是，“是什么控制了冻土带土壤中每单位N可供植物吸收的碳的流失量？”这个问题很重要，因为冻土带生态系统中植物C的获得往往受到氮的强烈限制，而冻土带生态系统中维管植物获得的几乎所有N都来自土壤有机质的微生物矿化。因此，生态系统的整体碳平衡在很大程度上取决于与氮吸收相关的植物碳吸收与土壤呼吸造成的碳损失之间的平衡。这项研究的设计遵循一个简单的概念模型，在该模型中，冻土带生态系统中的大量土壤有机质被视为由三个相互作用的有机质池组成，这些有机质库具有不同的周转时间和特征C：N比(微生物是调节其他三个库周转的第四个库，但也比其他三个库小得多)。总的假设是，冻土带土壤中可利用的C损失：N的平衡是由土壤有机质(包括新鲜凋落物)的化学性质和环境因素之间的相互作用控制的，环境因素决定了各种有机质库的相对分解和相互转化的速度。其他假设涉及(1)土壤有机质质量，(2)排水和相关的好氧/厌氧条件，以及(3)温度的单独影响。这些假设将通过测量土壤中的碳损失和有效氮来检验，这些土壤来自不同的冻土带生态系统类型，这些类型已经知道在初始有机物质质量上存在差异。一项野外实验将比较潮湿、潮湿和干燥的荒原苔原，两项实验室实验将比较潮湿和潮湿的苔原。一个实验室实验将在从田间运来的整个植物-土壤整体上进行，另一个实验室实验将仅在土壤上进行；处理将包括温度、排水以及N和P有效性的调控。将使用同位素示踪剂和不同土壤有机质组分中碳和氮同位素的自然丰度来帮助估计主要有机质库的相互作用和周转速度。由于实验是长期的(实验室实验将在研究的3年中模拟4个完整的生长季，野外测量将在1988年开始的实验的第10年至第12年进行)，因此有可能记录有机质储藏库本身的特征变化，以及进出有机质储存库的通量。除了用数据直接检验假设外，模拟模型(MBL-GEM)将被用作一个综合工具，用于较长期的预测，并与过去关于植被C-N相互作用的研究相结合。

9615563 Nadelhoffer Changes in terrestrial carbon cycles are often tightly constrained by interactions between C and other elements, especially N and P. The aim of this research is to improve the understanding of how carbon/nutrient interactions in soils might affect the responses of arctic tundra ecosystems to global environmental change. The research centers on the question, "What controls the amount of C lost from tundra soils per unit N made available for plant uptake?" This question is important because plant C gain in tundra ecosystems is often strongly N-limited, and virtually all of the N made available to vascular plants in tundra ecosystems comes from microbial mineralization of soil organic matter. Thus the overall C balance of the ecosystem is largely determined by the balance of plant C gains associated with N uptake versus C losses due to soil respiration. The design of the research is guided by a simple conceptual model, in which the large amount of soil organic matter in tundra ecosystems is viewed as being composed of three interacting organic matter pools with different turnover times and characteristic C:N ratios (microbes are a fourth pool that mediates turnover of the other three, but which is also much smaller than the other three). The overall hypothesis is that the balance of C lost: N made available in tundra soils is controlled by interactions between the chemical quality of soil organic matter (including fresh litter) and environmental factors that determine the relative rates of decomposition and interconversion of the various organic matter pools. Additional hypotheses deal with the individual effects of (1) soil organic matter quality, (2) drainage and associated aerobic/anaerobic conditions, and (3) temperature. These hypotheses will be tested by measuring C losses and N made available in soils from contrasting tundra ecosystem types that are already known to differ in initial organic matter quality. A field experiment will compare wet, moist, and dry heath tundras, and two laboratory experiments will compare wet and moist tundras. One laboratory experiment will be on whole plant-soil monoliths transported from the field, and the other laboratory experiment will be on soils only; treatments will include manipulations of temperature, drainage, and N and P availability. Isotopic tracers and natural abundances of C & N isotopes in various soil organic matter fractions will be used to help estimate interactions and turnover rates of the major organic matter pools. Because the experiments are long-term (the laboratory experiment will simulate 4 full growing seasons over the 3 years of the research, and the field measurements will be made in the 10th through the 12th years of an experiment begun in 1988), it may be possible to document changes in characteristics of organic matter pools themselves, as well as the fluxes into and out of them. In addition to direct tests of the hypotheses with data, a simulation model (MBL-GEM) will be used as a synthesis tool and for longer-term prediction and integration with past research on vegetation C-N interactions.