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

9615563 纳德尔霍费尔 陆地碳循环的变化通常受到C与其他元素（尤其是N和P）之间相互作用的严格限制。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苔原生态系统对全球环境变化的反应的了解。这项研究集中在这样一个问题上：“是什么控制了冻原土壤中每单位可供植物吸收的氮中损失的碳的数量？“这个问题很重要，因为苔原生态系统中植物碳的增加通常是强烈的氮限制，而苔原生态系统中维管植物几乎所有的氮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植物碳增益与氮吸收与土壤呼吸造成的碳损失的平衡。 该研究的设计是由一个简单的概念模型，在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与不同的周转时间和特征C：N比（微生物是第四池，介导其他三个周转，但也比其他三个小得多）。总的假设是，碳损失的平衡：在苔原土壤中提供的N是由土壤有机质（包括新鲜凋落物）的化学质量和环境因素，确定各种有机质池的分解和相互转化的相对速率之间的相互作用控制。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）温度的个体效应。 这些假设将通过测量来自对比冻原生态系统类型的土壤中的碳损失和氮来进行测试，这些生态系统类型已知在初始有机质方面存在差异 质量.一个野外实验将比较潮湿，潮湿和干燥的荒原苔原，两个实验室实验将比较潮湿和潮湿的苔原。一个实验室实验将是从现场运输的整个植物土壤整料，和其他实验室实验将仅对土壤;治疗将包括温度，排水，氮和磷的可用性的操纵。同位素示踪剂和自然丰度的C-N同位素在不同的土壤有机质组分将被用来帮助估计的主要有机质库的相互作用和周转率。由于实验是长期的（实验室实验将在3年的研究中模拟4个完整的生长季节，而实地测量将在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物池本身特性的变化，以及流入和流出它们的通量。除了用数据直接检验假设外，还将使用模拟模型（MBL-GEM）作为综合工具，进行长期预测，并与过去关于植被碳氮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.