The role of mycorrhizae and mycorrhizal networks in tree species range shifts with climate change nad disturbance

预计随着气候变化，加拿大的树种范围将发生巨大变化，通常是前缘向北迁移，后缘大量死亡。树木迁移的能力不仅取决于其遗传适应性，还取决于新环境的适宜性，包括土壤中是否存在相容的外生菌根真菌（EMF）、场地干扰的严重程度以及植物竞争的强度。之前预测树种分布范围变化的研究主要集中在气候和遗传因素上，而我的项目做出了新颖的贡献，即利用同位素示踪剂、分子生物学（宏基因组学、微卫星和 DNA 测序）和网络分析方面的尖端技术，在真实物种迁移实验中检查 EMF 和菌根网络 (MN) 的生物效应。在作为气候变化空间代理的区域干旱胁迫梯度中，我将研究以下作用：（1）局部电磁场在促进树木基因型向新环境迁移方面的作用； (2) 由成熟树木形成的 MN，促进自然更新，特别是密切相关（亲缘）基因型的树木； (3) MN重组和影响自然再生模式的干扰严重程度； (4) 改变植物间碳源汇梯度，将碳从树木死亡转移到生长。 对于（1），我将研究 EMF 在辅助迁移场和生长室实验中建立非本地树木基因型的作用。对于（2）和（3），我将在网袋处理中种植亲缘和非亲缘种子（控制 MN 的形成和复杂性），或者在自然间隙中，或者在去除不同级别的中心（高度连接）树木的收获处理中。对于（4），我将使用模拟自然树木衰老的落叶处理来操纵幼苗碳源-汇梯度。我的项目对 EMF 和 MN 促进树木范围变化的作用和机制，以及它们如何影响植物群落和土壤碳动态的贡献，将有助于科学家预测森林生态系统对气候变化的反应，并帮助管理者设计维持加拿大森林的恢复力、碳储存和适应能力的实践。

Tree species ranges are predicted to shift dramatically in Canada with climate change, typically with northward migration at the leading edges and extensive mortality at the trailing edges. The ability of trees to migrate will depend not only on their genetic suitability, but also the hospitability of the new environment, including the presence of compatible ectomycorrhizal fungi (EMF) in soil, the severity of site disturbance, and the intensity of plant competition. Whereas previous research predicting tree species range shifts has focused on climatic and genetic factors, my program makes the novel contribution of examining the contributing biotic effects of EMF and mycorrhizal networks (MNs) in real species migration experiments using cutting edge techniques in isotope tracers, molecular biology (metagenomics, microsatellites, and DNA sequencing) and network analysis. Across a regional drought-stress gradient serving as a spatial proxy for climate change, I will study the roles of: (1) local EMF in facilitating migration of tree genotypes to new environments; (2) MNs formed by mature trees in facilitating natural regeneration, particularly of closely related (kin) genotypes; (3) disturbance severity in reorganizing the MN and affecting natural regeneration patterns; and (4) shifting interplant carbon source-sink gradients in transfer of carbon from dying to establishing trees. For (1), I will examine the role of EMF in establishment of non-local tree genotypes within assisted migration field and growth chamber experiments. For (2) and (3), I will plant kin and non-kin seed in mesh bag treatments (controlling for the formation and complexity ot MNs) either in natural gaps or within harvesting treatments that remove different levels of hub (highly connected) trees. For (4), I will manipulate seedling carbon source-sink gradients using defoliation treatments emulating natural tree senescence. The contributions of my program on the roles and mechanisms by which EMF and MNs facilitate tree range shifts, and how these affect plant community and soil carbon dynamics, will help scientists to predict forest ecosystem responses to climate change and managers to design practices for maintaining the resilience, carbon storage, and adaptive capacity of Canada's forests.