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，人为的N沉积改变了N相对于P的化学计量比，并引起P的共同限制。树木应对营养缺乏的主要策略是与菌根真菌形成共生关系。主要菌根类型丛枝菌根(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固存)。越来越多的人认识到，主要通过预测模型，土壤N：P比的增加触发了森林组成从EM树种向AM树种优势的转变。这一转变涉及到土壤碳储量的减少，并对生态系统功能产生了强烈的负面影响。然而，主要树科(壳斗科、松科、杨柳科、桃金娘科)的属能够在同一物种内形成两种类型的菌根。双菌根对生态系统过程的作用机制以及它们对人为土壤养分变化的响应仍处于起步阶段。本研究的目的是在改良的土壤N：P比例下，研究树木与土壤真菌的相互作用，使我们能够理解和量化树种内菌根类型转变对森林生态系统过程的影响。具体地说，我将1)在三个不同的树木模式系统-针叶-道格拉斯冷杉、阔叶-黑杨和磷敏感的澳大利亚Jarrah中，将与根相关的真菌群落和菌根类型的变化与土壤N：P比率联系起来，2)通过酶谱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，以及3)测量一个树种内菌根类型的转移和/或真菌功能群落的变化对树木生产力、叶凋落物分解和土壤真菌生物量的影响。这项研究的结果将有助于制定具体的策略(例如，增加生态系统对环境变化的适应能力的适应性森林管理(物种选择)。

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.