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

点击翻译按钮获取中文摘要

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.*****