Physiology and genetics of nitrogen uptake and metabolism in trees

植物面临着扎根的独特挑战。它们必须在一生中从有限的土壤中获得养分--就树木而言，需要几个世纪的时间。在加拿大，森林土壤通常是寒冷、酸性的，有效养分含量很低，特别是氮。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，是一个重要的实用和科学目标。在自然系统中，树根与真菌伙伴菌根共生，菌根对养分的矿化、吸收和向宿主的转移至关重要。菌根物种在分解有机物和吸收养分的能力以及对非生物因素的反应方面有所不同。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以及温度或二氧化碳对这些共生生物的影响知之甚少。这项建议描述了一个关于树根及其相关菌根真菌的研究计划，以及在不同的温度、氮素有效性和二氧化碳条件下，这些共生体对氮素吸收和氮素形态偏好的影响。该项目之前的研究仅集中在树根对氮的吸收上。我们记录了物种间和物种内养分吸收和利用效率的遗传差异，并发现土壤温度影响氮的吸收形式。随着全球气温上升，这些影响将对森林生长和社区结构产生重大影响。未来的研究将对树木和菌根物种进行对比研究，以了解根温度如何影响细胞和全根水平上氮素吸收的速度和形式，氮素吸收所必需的基因的表达，以及二氧化碳如何影响树木和真菌之间的氮碳平衡。这项工作将加深我们对菌根共生功能多样性的理解，并将揭示森林应对全球变化的潜在复杂性。这项研究是为培训五名研究生和一些本科生而设计的，他们将成为NSERC森林和气候变化创造计划的一部分。

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.