THE ROLE OF MYCORRHIZAE IN WATER USE IN NORTHERN HARDWOOD: IS TRANSPIRATION OPTIMIZED FOR UPTAKE LIMITING NUTRIENTS

Transpiration is a key ecohydrologic process that requires better understanding, especially considering the need to manage forests under future climates and altered nutrient regimes. Forest fertilization alters transpiration for reasons that are not well understood. This project will use a set ofpreviously established, replicated, nitrogen, phosphorus, and calcium treatments in New Hampshire to provide insight into the mechanisms behind observed effects of nutrient availability on transpiration.Current models of forest hydrology generally consider evapotranspiration to be a function of vegetation type, atmospheric evaporative demand, and water availability. The role of nutrient availability in determining plant water use has not been adequately explored, and our focus on the role of mycorrhizal fungi in this relationship is novel. The fungal measurements in fertilized plots will also provide evidence of how both ectomycorrhizal and arbuscular mycorrhizal communities reorganize after N, P, or Ca addition. Further, this project will test whether water use and plant and fungal responses are consistent with nutrient optimization theory, using a combination of model simulations and field measurements of nutrient uptake capacity.The role of mycorrhizal networks in water use has not been comprehensively addressed, and Ca and P have been relatively little studied compared to N in terms of their effect on mycorrhizal communities in forested ecosystems. Testing the optimality of water use will contribute to resource optimization theory. This study will contribute to graduate and undergraduate student training and produce theses and articles in peer-reviewed journals.