CAREER: Microbial Mediation of Temperate Tree Responses to Climate Change

Harvard University, Cambridge MA

Investigators

Abstract

Understanding how forests will function under future climate conditions is critical for predicting changes to the global carbon cycle and managing forest ecosystems. Global change is a complex issue involving many interacting drivers. As carbon dioxide accumulates in the atmosphere, this will increase temperatures, which will influence precipitation patterns. However, most experiments simulating global change scenarios in forest ecosystems manipulate only one or two factors at a time, limiting our ability to predict whether rising CO2, warming, and precipitation changes will have interacting or exacerbating effects on tree growth and forest function. This project establishes the Forest Responses to Warming, Atmospheric CO2 and Drought (FORWARD) experiment, which simulates future atmospheric CO2 concentrations, warmed temperatures, and increased drought exposure on temperate forest species that represent a diversity of growth strategies. The project examines how each global change factor and their combined effects impact tree physiology, growth, carbon capture, and the strategies that different tree species use to obtain soil resources. This work improves efforts to predict how temperate forest species will respond to more realistic future global change scenarios. Despite strong mechanistic evidence that CO2, warming, and drought will have compounding effects on forest function, relatively few attempts have been made to experimentally assess the interactions between these climate change factors. Further complicating how forests will respond to climate change is the fact that symbiotic relationships between trees and arbuscular mycorrhizal fungi (AM), ectomycorrhizal fungi (EM), and nitrogen-fixing bacteria (N-fixers) represent different strategies for obtaining water and nutrients that could lead to fundamentally different responses to climatic change. Given these differences, assessing the responses of these major tree-microbe symbioses to interacting components of climate change is critical to making realistic predictions of how forests will respond to future climate conditions. The FORWARD experiment manipulates atmospheric CO2 using Free-Air CO2 Enrichment, warming temperatures using aboveground heat lamps and belowground heating cables, and increased drought using throughfall shelters. Responses of trees and their associated microbes to these factorial manipulations demonstrate 1) the interacting and compounding effects of CO2, warming, and drought on temperate forest trees, 2) differences in physiological and growth responses of AM, EM, and N-fixing species to global change, and 3) how different responses of symbiotic groups influence future tree and soil carbon storage. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.