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

在拟议的研究中，我将在常见的园林试验中测量几个常见树种下森林地面氮循环过程的总速率和净速率，以确定树种之间N循环的差异，以及对确定不同树种下森林地面主要N形态和N通量最有影响的枯枝落叶或森林地上部分的特征。这将告诉我们，为了林业、开垦或协助迁徙以应对气候变化，引入一种新的树种将如何改变场地，特别是氮循环和有效性。我还将比较不同气候、植被和土壤的天然林中的N循环，这将为了解天然林中的土壤N循环以及影响这些循环性质的因素提供新的见解。 准确的分解预测和建模对于可靠地预测全球变化下生态系统中碳通量和平衡的变化至关重要。我将测试两种拟议的方法，以提高我们预测凋落物分解速度的能力-通过确定一个因素对其产生压倒性影响的阈值，以及确定准确预测凋落物分解速度的植物功能性状。为此，我将使用长期实地实验的数据和样本，测量包括粗木质碎屑在内的凋落物的腐烂速度。最后，我将测试改变了我们对分解的看法的新假设--真正的木质素很早就开始分解，在分解早期最活跃，而且在早期分解过程中“木质素”的明显积累是由于新化合物的积累，而不是顽固的植物材料的持久性。我将通过测量腐烂不同阶段枯枝落叶中克拉森“木质素”和真木质素浓度的变化来测试这一点，以确定这些假设是否适用于地表有机层发生分解的北方森林。这些研究将测试新的概念，并提高我们预测和模拟森林土壤碳通量的能力。

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.