Collaborative Research: Effects of Elevated CO2 on Forest N Cycling: Assessment with Large-Scale 15N Tracers and Modeling

抽象的。 森林生态系统每年与大气交换大量的碳（C），这种交换受到养分循环的强烈限制。预计森林生产力将随着下一个世纪大气中二氧化碳浓度增加一倍而增加。研究和综合的一个关键领域是CO2浓度升高对土壤氮循环的反馈效应。 CO2浓度升高显着增加植物生产力，从土壤中的N的吸收和C的土壤微生物的通量，但不改变凋落物化学，分解，生态系统之间的N的质量平衡池，总和净N矿化或植物N的可用性。即使植物氮的可用性没有增加CO2浓度升高，有没有迹象表明，N是逐步限制这个生态系统的生产力提高，现在在它的第六个生长季节CO2浓度升高。这一结果是令人惊讶的，考虑到（i）净初级生产力是明显的N限制在这个生态系统中，（ii）有激烈的竞争，为可用的N之间的植物，微生物和非生物汇在土壤中，（iii）的长期生产力的一个单一的原型FACE图在这个研究地点是刺激CO2浓度升高后，只有增加氮肥。这些结果表明，在我们的理解森林生态系统中的C和N循环的耦合性质的一个根本的差距，并有机会扩大我们的生态系统地球化学的知识。这项研究将通过解决美国东南部2400多万公顷林地生态系统中碳固存的主要潜在限制，对社会产生直接效益;这些生态系统可能根据京都议定书对其碳汇潜力进行管理。鉴于杜克森林FACE实验的跨学科和多机构性质，这项研究的影响将远远超出这个合作团队。这笔赠款将用于培训未来的科学家，招聘和留住女研究生，并将通过积极参与SEEDS方案（欧空局和联合国儿童基金会的一个联合方案），努力扩大少数民族的参与。 该项目将通过向国家环境评估中心和15个氮示踪剂研究点的国际网络的当前综合活动提供数据集和增强模型，加强研究基础设施。我们预计这项工作的影响将继续很高，无论是在基础生态系统科学的进步，并在生态系统科学的全球变化问题的可证明的应用，这些问题将越来越多地影响社会在下一个世纪。

Abstract. Forest ecosystems exchange large amounts of carbon (C) with the atmosphere each year, an exchange that is strongly constrained by nutrient cycling. Forest productivity is anticipated to increase with the projected doubling in the concentration of atmospheric CO2 over the next century. A critical area for research and synthesis concerns the feedback effects of elevated CO2 on soil N cycling. Elevated CO2 significantly increased plant productivity, the uptake of N from soils and the flux of C to soil microbes but did not change litter chemistry, decomposition, the mass balance of N among ecosystem pools, gross and net N mineralization or plant N availability. Even though plant N availability did not increase under elevated CO2, there is no indication that N is progressively limiting the enhanced productivity of this ecosystem now in it sixth growing season under elevated CO2. This result is surprising given that (i) Net Primary Productivity is demonstrably N limited in this ecosystem, (ii) that there is intense competition for available Namong plants, microbes and abiotic sinks in soils, and (iii) that the long-term productivity of asingle prototype FACE plot at this research site was stimulated by elevated CO2 only after the addition of N fertilizer. These results suggest a fundamental gap in our understanding of the coupled nature of C and N cycles in forest ecosystems, and an opportunity to expand our knowledge of ecosystem biogeochemistry. This research will have direct benefits to society by addressing a major potential limitation to C sequestration in ecosystems that cover over 24 million hectares of forest land in the southeastern US; ecosystems that are likely to be managed for their C-sink potential under the Kyoto Protocol.Broader Impacts: Given the interdisciplinary and multi-institutional nature of the Duke Forest FACE experiment, this research will have impacts that extend well beyond this collaborative team. This grant will train future scientists and recruit and retain women graduate students, and will make an effort to broaden the participation of minorities by actively participating in the SEEDS program (a joint program of ESA and UNCF). This project will enhance infrastructure for research by contributing data sets and an enhanced model to current synthesis activities at NCEAS and an international network of 15 N tracer study sites. We expect the impact of this work to continue to be high, both in advances to fundamental ecosystem science, and in the demonstrable application of ecosystem science to issues of global change; issues that will increasingly impact society over the next century.