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

点击翻译按钮获取中文摘要

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.