Using Phylogenetically Independent Contrasts to Examine Temperature Acclimation of Root and Mycorrhizal Fungal Respiration Among Organisms from Broad Latitudinal Gradients

David M. Eissenstat and Roger T. Koide, Penn State University

February 1, 2003 - January 3, 2006. Funded by NSF IBN-Ecological and Evolutionary Physiology.

Temperature is a major constraint on mycorrhizal root metabolism in many environments. In cold climates, temperatures in the spring restrict root metabolism and nutrient acquisition. In the summer in temperate and tropical climates, unshaded soils may reach temperatures that cause excessive carbohydrate metabolism unless root acclimation occurs. The central objective of this proposal is to examine how latitude of origin affects plant root and mycorrhizal fungal respiratory responses to soil temperature. These investigations will use phylogenetically independent contrasts (contrasts using distinct evolutionary lineages) to permit general inferences on plant and mycorrhizal fungal responses to temperature as a function of latitude of origin. The research will focus on four, interrelated hypotheses associated with organism response to temperature. Does diurnal temperature variation affect an organism's ability to acclimate to temperature? Under conditions of no acclimation, do plants and mycorrhizal fungi from higher latitudes exhibit higher respiration than those from lower latitudes when measured at the same temperature? Under conditions where acclimation occurs, do plants & mycorrhizal fungi from high latitudes exhibit less acclimation to high temperature (i.e., excessively metabolize carbohydrates) than those from lower latitudes? Are the independent mycorrhizal fungal or plant respiratory responses to temperature the same when the organisms are measured in symbiosis? The use of multiple, distinct evolutionary lineages of both fungi and plants will provide new insight into how organisms respond globally to both average temperatures and temperature variation.

This work has several opportunities for broader scientific impacts. Global climate change is an area of intense interest to both scientists and government policy makers. The Intergovernmental Panel on Climate Change predicts a 1.4-5.8 °C increase in global surface temperature by 2100, using atmospheric models that assume increases in atmospheric CO2 will lead to increases in ambient temperature, which increases soil respiration, causing a positive feedback. Mycorrhizal root respiration represents the dominant source of soil respiration in many soils. If mycorrhizal roots acclimate to increases in temperature, than predicted increases in surface temperatures may be overestimated.