Evaluating relationships between plant traits and nitrogen use to help predict species' responses to climate change

Abstract

In many ecosystems, nitrogen (N) is the predominant nutrient limiting plant growth. Plants have therefore developed diverse strategies to compete for and partition soil N resources to ensure an adequate N supply. Differences in how plants acquire N may be important for predicting plant responses to different global changes. In particular, how species respond to climate change may depend on their N use strategy since climate change will likely alter the forms of N available to plants as well as total N availability. However, there remain key gaps in our understanding of plant N acquisition that impede our ability to project the impacts of climate change on plant communities. My research focuses on one of these gaps, the variation in plant use of different chemical forms of N, and examines how that variation can influence plant responses to climate change. Specifically, my research aims to increase our understanding of N acquisition in trees by examining whether plant traits can improve our ability to identify and explain differences in the use of different N forms. My first three chapters explore (1) the relationship between N uptake rates and root morphology for different N forms; (2) whether plant traits can help explain how species vary in their growth on different N forms; and (3) whether warming and drought alter patterns of N use in a regenerating forest. I then examine (4) how plant nutrient acquisition strategies and traits influence links between ecosystem carbon (C) and N cycling. Together, my research highlights that plants differ in their capacity to use different forms of N, which are in some cases associated with their traits. I also show that plants differ in how they partition N resources in the field, especially between mycorrhizal types. Finally, I show that both species’ mycorrhizal type and phylogeny contribute to differences in C and N cycling in ecosystems where they dominate. Overall, my research adds to our knowledge of how plants acquire N and shows that these strategies are an important influence on species and ecosystem responses to global change.