Physiology and genetics of nitrogen uptake and metabolism in trees

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有限的土壤中获取养分——就树木而言，需要几个世纪。在加拿大，森林土壤通常是冷的、酸性的，有效养分，特别是氮(N)含量低。了解树木对这些土壤的适应，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、吸收和向宿主转移至关重要。菌根菌种在分解有机物和吸收营养物的能力以及对非生物因素的反应方面各不相同。这对气候变化中的树木营养具有重要意义。我们对菌根之间的变化知之甚少，也不知道温度或二氧化碳对这些共生的影响。本文介绍了在不同温度、氮效度和CO2条件下，根系及其相关菌根真菌对氮吸收和氮形态偏好的影响。

Plants face the unique challenge of being rooted in place. They must acquire nutrients from a limited volume of soil over an entire lifetime - in the case of trees, over centuries. In Canada, forest soils are typically cold, acidic and low in available nutrients, particularly nitrogen (N). Understanding the adaptations of trees to these soils, and how these 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 nutrient mineralization, uptake and transfer to the host. Mycorrhizal species differ in their ability to break down organic matter and take up nutrients, and in their response to abiotic factors. This has important implications for tree nutrition in changing climates. We know little about variation among mycorrhizae or about the effects of temperature or CO2 on these symbioses. This proposal describes a program of research on tree roots and their associated mycorrhizal fungi, and the effects of these symbioses on N uptake and N-form preference under contrasting temperatures, N availability and CO2. Previous research in this program has focused on N uptake by tree roots, alone. We have documented genetic variation among and within species in nutrient uptake and use efficiency, and found that soil temperature affects the form in which N is taken up. As global temperatures rise, these effects will have significant implications for forest growth and community structure. Future research will investigate contrasting tree and mycorrhizal species to understand how root temperature affects 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 affects the N-carbon balance between the tree and fungus. This work will deepen our understanding of the functional diversity in mycorrhizal symbioses, and will reveal potential complexities in forest response to global change. The research is designed for the training of five graduate students and a number of undergraduates who will be part of the NSERC CREATE Program in Forests and Climate Change.