Combined Use of 15N Natural Abundances and Tracers to Elucidate Above- and Belowground C and N Cycle Linkages during Forest Succession

目前，整个北温带重新种植的森林减少了约15%的化石燃料二氧化碳(CO2)排放。然而，目前尚不清楚这些森林将在多长时间内以及在多大程度上继续隔离二氧化碳，从而抵消很大一部分人类产生的二氧化碳排放。最近的测量表明，与长期持有的生态系统二氧化碳吸收随着时间的推移下降到零的观点相反，森林在建立后可以继续储存碳几个世纪。要做到这一点，氮循环模式和速率必须随着森林树种组成在演替过程中的变化而改变。然而，这是如何发生的还不是很清楚，所以这个项目将调查氮循环影响碳吸收的机制。这项研究将在密歇根州北部的一个大规模、大胆的试验性森林环境中使用新的、多尺度的、稳定的氮同位素方法进行，在那里，树干环剥正在加速成熟的、早期演替的树种的损失。实验森林的碳吸收正在与附近的一片单独资助的非人工森林进行比较。这项由美国国家科学基金会资助的研究重点是晚期演替树种、真菌共生体和土壤之间的氮素交换，因为它们控制着森林的碳平衡。研究结果将使人们更全面地了解演替阶段对森林生长的控制，并将改进对温带森林二氧化碳吸收和碳平衡的预测。这项研究将作为“从幼儿园到灰色”环境教育的资源，从这项研究得出的见解将为政策制定者和资源管理者关于森林碳固存和提供生态系统服务的决策提供参考。

Re-growing forests across the North Temperate Zone presently remove about 15% of fossil fuel carbon dioxide (CO2) emissions. It is unclear, however, how long and to what extent these forests will continue to sequester CO2 and thereby offset a major fraction of human-derived CO2 emissions. Recent measurements suggest that, in contrast to the long-held idea that ecosystem CO2 uptake declines to zero over time, forests can continue storing carbon for centuries after establishment. For this to occur, nitrogen cycling patterns and rates must change as tree species composition of the forest shifts during succession. How this occurs is not well understood, however, so this project will investigate mechanisms by which nitrogen cycling influences carbon uptake. The research will be conducted using novel, multi-scale, stable nitrogen isotope approaches in a large-scale, bold, experimental forest setting in northern Michigan where losses of maturing, early successional tree species are being accelerated by stem girdling. Carbon uptake by the experimental forest is being compared to a nearby non-manipulated forest under separate funding. The NSF-supported research here focuses on nitrogen exchanges between late-successional tree species, their fungal symbionts and soils as they control forest carbon balances. Results will provide a more complete understanding of controls on forest growth across successional stages and will improve predictions of temperate forest CO2 uptake and carbon balances. The study will serve as a resource for 'Kindergarten-to-Gray' environmental education and insights derived from this research will inform decisions of policymakers and resource managers regarding forest carbon sequestration and provision of ecosystem services.