Ecophysiology of ectomycorrhizal symbioses

外生菌根是真菌与植物根系之间古老的共生关系。松树、桦树、柳树和山毛榉科的许多成员都严重依赖这些真菌伙伴来充分吸收矿物质营养。在我的实验室里，我们研究了外生菌根真菌（EMF）的双重功能：作为共生体，可以将氮(N)、磷(P)和其他矿质营养物质转运给它们的植物伙伴；作为土壤真菌，通过排泄降解酶，有助于土壤有机质的分解和碳(C)、氮、磷和硫(S)的循环。由于EMF在植物养分吸收中起着重要作用，因此它们在树木响应环境变化的迁移或适应中将发挥重要作用。我们计划调查不同的EMF群落是否使用不同的策略来获取P，这取决于它们所在土壤中占主导地位的P的类型（有机与无机）。如果EMF社区是在当地适应的，那么如果由于气候变化而改变了重新种植计划，森林管理者将需要同时管理树木和EMF。我的一个学生最近观察到，在一段时间的饥饿后，当松树幼苗的EMF被提供营养时，它们的N会大量流失。这表明氮从幼苗转移到真菌，这与传统的共生认识相反。我们将通过用15N标记叶子和菌丝来验证这一假设，并使用质谱法和复杂的显微方法定量N在两个方向上的易位。如果证实植物向EMF的氮迁移，我们将与国际专家合作研究菌根根根-真菌界面上氮转运体的行为。我们还将在田间和温室中跟踪松树幼苗的萌发和定植，看看我们是否能发现土壤养分状况突然变化后N运输方向的任何短期变化。本研究将挑战外生菌根植物中氮转运的传统观点，特别是在幼苗建立过程中，并增加对菌根界面氮转运的认识。虽然人们普遍认为EMF会分解土壤有机质以获取N、P和S，但鉴于EMF可以直接获取植物宿主根系中最近固定的C，因此关于EMF是否能满足土壤C的任何C需求存在很多争论。我们将在实验室中通过种植带有13c标记的土壤C的外生菌根松来测试EMF的腐养行为。我们将通过分析EMF磷脂中的C同位素特征来量化从土壤中获得的C与根的比例。通过这项研究，在国际合作者的参与下，四名荣誉学生，三名硕士和两名博士将接受培训，使用复杂的显微镜，同位素和分子技术来研究电磁场如何影响加拿大森林中的幼苗建立和养分循环。

Ectomycorrhizae are ancient symbiotic relationships between fungi and plant roots. Many members of the pine, birch, willow and beech families depend heavily on these fungal partners for adequate uptake of mineral nutrients. In my lab, we look at the dual function of ectomycorrhizal fungi (EMF): as symbionts that can translocate nitrogen (N), phosphorus (P) and other mineral nutrients to their plant partners, and as soil fungi that, by excreting degradative enzymes, contribute to the breakdown of soil organic matter and the cycling of carbon (C), N, P and sulphur (S). Because EMF play a major role in plant nutrient uptake, they will be important in the migration or adaptation of trees in response to environmental change. We plan to investigate whether different EMF communities use different strategies for acquiring P depending on the types of P (organic vs inorganic) that dominant the soils in which they are found. If EMF communities are locally adapted, forest managers will need to manage both the trees and EMF if replanting programs are changed as a result of climate change. One of my students recently observed a major loss of N from pine seedlings when their EMF were supplied with nutrients after a period of starvation. This suggests that N moved from seedling to fungus, which is counter to conventional understanding of the symbiosis. We will test this hypothesis by labelling foliage, as well as hyphae, with 15N and quantify translocation of N in both directions using both mass spectrometry and sophisticated microscopic approaches. If movement of N from plant to EMF is confirmed, we will collaborate with an international expert to study behavior of N transporters at the root-fungal interface in mycorrhizal roots. We will also follow the germination and colonization of pine seedlings in the field and greenhouse to see if we can detect any short-term shift in the direction of N transport after a sudden change in soil nutrient status. This research will challenge the conventional view of N transport in ectomycorrhizal plants especially during seedling establishment, and increase understanding of N transport at the mycorrhizal interface. While it is accepted that EMF break down soil organic matter to access N, P and S, there is much debate about whether EMF meet any of their C needs from soil C, given that they have direct access to recently fixed C in roots of their plant hosts. We will test for saprotrophic behavior of EMF in the lab by growing ectomycorrhizal pine with 13C-labelled soil C. We will quantify the proportion of C acquired from soil vs roots by analyzing C isotope signatures in the phospholipids of the EMF. Through this research, and with the involvement of international collaborators, four honours, three MSc, and two PhD students will be trained in the use of sophisticated microscopic, isotopic and molecular techniques to study how EMF affect seedling establishment and nutrient cycling in Canadian forests.