Physiology and genetics of nitrogen uptake in the tree/mycorrhizal holobiont

植物面临着扎根的独特挑战。它们必须在整个生命周期中从一个地方获取营养对于树木来说，需要几个世纪。北方森林树木面临着额外的挑战，因为土壤通常是寒冷、酸性的，有效养分，特别是氮(N)含量低。了解树木对氮限制土壤的适应，以及这些适应如何影响树木对气候变化的反应是一个重要的实践和科学目标。在自然系统中，树根与真菌伙伴菌根相关联，对养分矿化、吸收和转移过程至关重要。有些人甚至认为这棵树不是一个独立的实体，而是一个整体，依赖于它的微生物群。菌根类型和种类在分解有机物和吸收养分的能力上有所不同，但我们对菌根之间的变化以及温度和二氧化碳对共生关系的影响知之甚少。本研究旨在研究树木根系与外生和丛枝菌根真菌的相互作用，以及在不同温度、氮有效性和CO2条件下菌根对氮的吸收和形态偏好。我们将探索寄主植物和微生物伴侣基因型的相互作用，重点关注寄主植物的生长和营养。我过去的工作主要集中在针叶树和外生菌根真菌之间的伙伴关系。我们已经证明，真菌物种之间与N相关的功能性状的差异是对不同N形态有效性的适应，真菌伴侣在控制N吸收方面起着关键作用。本研究的目的是评估树木与菌根菌种和基因型之间的相互作用，以及N形态有效性、温度和CO2等环境因子。随着全球气温上升和土壤变暖，这些相互作用将对氮吸收产生重大影响，从而影响森林生长和群落结构。我将研究细胞和全根水平上氮吸收的速率和形式，氮吸收的基因表达，以及二氧化碳浓度如何影响树木和真菌之间的N-碳平衡。这项工作将加深我们对菌根共生功能多样性的认识。它将揭示森林应对全球变化的潜在复杂性以及改善森林生长的手段。这项研究是为在维多利亚大学森林生物学中心培训四名研究生和十名本科生而设计的。

Plants face the unique challenge of being rooted in place. They must acquire nutrients from one location over an entire lifetime in the case of trees, over centuries. Northern forest trees face an additional challenge because soils are typically cold, acidic and low in available nutrients, particularly nitrogen (N). Understanding the adaptations of trees to N-limited soils, and how these adaptations may shape tree response to changing climates is an important practical and scientific goal. In natural systems, tree roots associate with fungal partners, mycorrhizae, that are vital to the processes of nutrient mineralization, uptake and transfer. Some go so far as to suggest that the tree is not a standalone entity but a holobiont, dependent on its microbiota. Mycorrhizal types and species differ in their ability to break down organic matter and take up nutrients, but we know little about variation among mycorrhizae or about temperature or CO2 effects on the symbiosis. This proposal describes a program of research on the interaction of tree roots with ecto- and arbuscular mycorrhizal fungi, and the N uptake and N-form preferences of the mycorrhizae under conditions of contrasting temperature, N availability and CO2. We will explore the interaction of genotypes of host plant and microbial partner, with a focus on the growth and nutrition of the host plant.My past work has focused on the partnership between conifers and ectomycorrhizal fungi. We have shown that differences in N-related functional traits among fungal species are adaptations to varying N form availability, and that the fungal partners play a key role in controlling N uptake. The objective of the proposed research is to evaluate the interactions among tree and mycorrhizal species and genotypes, and the environmental factors of N form availability, temperature and CO2. As global temperatures rise and soils warm, these interactions will have significant implications for N uptake, and thus forest growth and community structure. I will investigate the rate and form of N uptake at the cellular and whole-root level, the expression of genes integral to N uptake, and how CO2 concentration affects the N-carbon balance between the tree and fungus.This work will deepen our understanding of the functional diversity in mycorrhizal symbioses. It will reveal potential complexities in forest response to global change and means to improve forest growth. The research is designed for the training of four graduate students and ten undergraduates in the UVic Centre for Forest Biology.