The shifts in mycorrhizal symbionts within individual tree species under anthropogenic soil nutrient alteration - the effects on forest ecosystem processes

温带和北方森林生态系统被认为主要是氮（N）有限的。然而，人为氮沉降改变了氮相对于磷（P）的化学计量比，并引起P的共同限制。树木科普养分缺乏的主要策略是与菌根真菌形成共生。主要的菌根类型，丛枝菌根（AM）和外生菌根（EM）在碳（C）和养分循环机制上不同，对森林生态系统过程的影响也不同（例如，C螯合）。人们越来越多地认识到，主要是通过预测模型，土壤N：P比的增加触发了森林组成从EM到AM树木占主导地位的转变。这种转变涉及土壤碳储量的减少，对生态系统功能产生强烈的负面影响。然而，来自主要树木科（壳斗科，松科，杨柳科，桃金娘科）的属能够在同一个体物种内形成双重共生的两种类型的菌根。双重菌根对生态系统过程的机制性影响的理解，以及他们对人为土壤养分变化的响应，仍然处于起步阶段，本提案的目的是调查下修改土壤N：P比，树木与土壤真菌的相互作用的规模，使我们能够理解和量化的结果，在一个树种内的菌根类型的转变对森林生态系统过程。具体来说，我将1）将根相关真菌群落和菌根类型的变化与土壤N：在三个不同的树木模型系统中，针叶树-道格拉斯冷杉，阔叶树-黑白杨，和磷敏感的澳大利亚贾拉，2）通过用酶谱法测量土壤酶的强度和空间分布来描述树木-土壤真菌相互作用的功能输出，3）测量一个树种内真菌功能群落的菌根类型转移和/或变化对树木生产力，凋落物分解，和土壤真菌生物量。这项研究的结果将有助于制定具体的战略（例如，物种选择）的适应性森林管理，提高生态系统对环境变化的适应能力。

Temperate and boreal forest ecosystems are considered to be primarily nitrogen (N) limited. However, anthropogenic N deposition changes the stoichiometry of N relative to phosphorus (P) and gives rise to P co-limitation. The primary strategy of trees to cope with nutrient deficiency is to form symbioses with mycorrhizal fungi. The dominant mycorrhizal types, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM) differ in carbon (C) and nutrient cycling mechanisms with divergent consequences on forest ecosystem processes (e.g., C sequestration). It is increasingly acknowledged, mainly through predictive models, that increasing of soil N:P ratio triggers the transition in forest composition from EM to AM trees dominance. This transition involves the decrease of soil C storages with a strong negative impact on ecosystem function. However, genera from major tree families (Fagaceae, Pinaceae, Salicaceae, Myrtaceae) are capable of forming both types of mycorrhizas in a dual symbiosis within the same individual species. The understanding of the mechanistic effects of dual mycorrhizas on ecosystem processes, as well as their response to anthropogenic soil nutrient change, is still in its infancy.The objective of this proposal is to investigate under the modified soil N:P ratio, the interactions of trees with soil fungi at a scale that enables us to understand and quantify the consequences of a shift in mycorrhizal type within a tree species on forest ecosystem processes. Specifically, I will 1) relate the changes in root-associated fungal communities and mycorrhizal type to soil N:P ratios in three distinct tree model systems, conifer - Douglas fir, broadleaf -Black poplar, and the P-sensitive Australian Jarrah, 2) describe the functional output of tree-soil fungi interactions by measuring the intensity and spatial distribution of soil enzymes by zymography, and 3) measure the effects of mycorrhizal type shift and/or changes in fungal functional communities within a tree species on tree productivity, leaf litter decomposition, and soil fungal biomass.The results of this research will contribute to developing specific strategies (e.g., species selection) of adaptive forest management that increase the ecosystem resilience to environmental change.