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制约。预计在下个世纪，随着大气二氧化碳浓度翻一番，森林生产力将会提高。二氧化碳浓度升高对土壤氮素循环的反馈效应是研究和合成的一个关键领域。CO2浓度升高显著增加了植物生产力、土壤对N的吸收和C向土壤微生物的通量，但没有改变凋落物的化学组成、分解、生态系统池之间的N物质平衡、N的总矿化和净N矿化以及植物N的有效性。尽管植物氮的有效性在二氧化碳升高的情况下没有增加，但没有迹象表明，氮正在逐步限制这一生态系统在二氧化碳升高下的第六个生长季提高的生产力。这一结果令人惊讶，因为(I)净初级生产力在该生态系统中明显受到氮的限制，(Ii)植物、微生物和土壤中非生物汇之间对有效氮的激烈竞争，以及(Iii)本研究地点单一样地的长期生产力仅在增施氮肥后才受到二氧化碳增加的刺激。这些结果表明，我们在理解森林生态系统中碳和氮循环的耦合性质方面存在根本差距，这是扩大我们对生态系统生物地球化学知识的机会。这项研究将通过解决美国东南部覆盖超过2400万公顷林地的生态系统中碳封存的主要潜在限制，以及根据《京都议定书》可能因其碳汇潜力而受到管理的生态系统，对社会产生直接好处。更广泛的影响：鉴于杜克森林面对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。这笔赠款将培训未来的科学家，招募和留住女性研究生，并将通过积极参与SEED计划(欧空局和联合国儿童基金会的联合计划)，努力扩大少数群体的参与。该项目将通过为NCEAS和一个由15个示踪剂研究地点组成的国际网络的当前综合活动贡献数据集和改进的模型，来加强研究的基础设施。我们预计，这项工作的影响将继续很大，无论是在基础生态系统科学方面的进展，还是在生态系统科学在全球变化问题上的明显应用；这些问题将在下个世纪对社会产生越来越大的影响。

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.