Litter decomposition and nitrogen cycling in forest soils: influences of tree species and site factors

在拟议的研究中，我将在普通园林实验中测量几种常见树种下森林地面N循环过程的总速率和净速率，以确定树种间N循环的差异程度，以及对不同树种下森林地面N优势形态和N通量影响最大的凋落物或森林地面的特征。这将告诉我们，为了应对气候变化而引入一种新的树种，用于林业、开垦或辅助迁徙，将如何改变场地，特别是氮循环和可用性。我还将比较不同气候、植被和土壤条件下天然林的N循环，这将为天然林土壤N循环以及影响这些循环性质的因素提供新的见解。

In the proposed research, I will measure gross and net rates of N cycling processes in forest floors under several common tree species in common garden experiments to establish how divergent N cycling is amongst tree species, and the characteristics of the litter or forest floors that are most influential in determining the dominant N forms and N fluxes in forest floors under different tree species. This will inform us as to how introducing a new tree species for purposes of forestry, reclamation or assisted migration in response to climate change will alter the site, particularly nitrogen cycling and availability. I will also compare N cycling in natural forests that differ in climate, vegetation and soil, which will provide new insights into soil N cycling in natural forests and the factors that influence the nature of these cycles. Accurate prediction and modeling of decomposition is essential to reliably predicting changes in carbon fluxes and balances in ecosystems under global change. I will test two proposed means to improve our ability to predict rates of litter decomposition - through identification of thresholds at which one factor exerts overwhelming influence, and of plant functional traits that accurately predict rates of litter decomposition. For this I will use data and samples from long-term field experiments measuring rates of decay of litter including coarse woody debris. Finally I will test new hypotheses that have transformed our thinking about decomposition - that decomposition of true lignin begins early and is most active early in decomposition, and that the apparent accumulation of "lignin" during early decomposition is due to the accumulation of new compounds rather than persistence of recalcitrant plant material. I will test this by measuring changes in concentrations of Klason "lignin" and true lignin in litter at various stages of decay, to determine if these hypotheses apply to northern forests in which decomposition occurs in surface organic layers. These studies will test new concepts and improve our ability to predict and model carbon fluxes from forest soils.