Metabolic Response To Temperature By Soil Microorganisms
Open Access
- Author:
- Malcolm, Glenna Marjorie
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 03, 2007
- Committee Members:
- Roger Tai Koide, Committee Chair/Co-Chair
David Eissenstat, Committee Member
Jonathan Paul Lynch, Committee Member
Howard Skinner, Committee Member - Keywords:
- respiration
temperature
ectomycorrhizal fungi
decomposer microorganisms
Q10
global warming - Abstract:
- Because of quick changes in temperature in forest litter between and within seasons and the anticipated continued increase in global surface temperatures, it is important to better understand the metabolic response to temperature by soil microorganisms. Notably, researchers have revealed that different soil dwellers may not metabolically respond to temperature in similar manners. In the case of ectomycorrhizal fungi, their respiration comprises a significant portion of total soil respiration, which is a flux ten times greater in size than that from fossil fuel emissions. Concern exists that a positive feedback may occur between soil respiration and temperature. If ectomycorrhizal fungi are capable of adjusting their metabolic response to temperature, they might partially ameliorate that feedback. In the case of decomposer communities, their activity digests organic soil carbon pools, a large amount of which is found in temperate and boreal forests across the globe. Small proportional changes in the concentration of carbon in soil may cause forest soils to be a large source or sink of carbon dioxide to the atmosphere. Again, the metabolic response of decomposer communities to temperature might determine the size of their carbon demand on forest soils, or put another way, how much CO2 they return to the atmosphere. The goal of my research was, therefore, to assess the metabolic response to temperature by ectomycorrhizal fungi and decomposer microorganisms at a variety of time scales. On a shorter time scale, I examined whether ectomycorrhizal fungi acclimated their respiration to three different incubator temperatures over the course of one week. Out of 12 ectomycorrhizal fungal isolates, Suillus intermedius, Cenococcum geophilum, and Lactarius cf. pubescens exhibited significant acclimation to temperature. Ectomycorrhizal fungal isolates also displayed significant differences in temperature sensitivity, or Q10. As the earth warms, those ectomycorrhizal fungi that acclimate to temperature will demand less carbon from their host plant and will add less carbon to the atmospheric carbon dioxide pool than those that do not. The fact that variation occurs among ECM fungal species in their ability to acclimate and in their sensitivity to temperature indicates that the response of the ectomycorrhizal fungal community as a whole will be determined by the structure of that community. On an evolutionary time scale, I investigated whether ectomycorrhizal fungi collected from contrasting latitudes vary in their respiratory response and sensitivity to temperature. Respiration by ectomycorrhizal fungi from Alaska was higher than that of fungi from Pennsylvania across measurement temperatures, when compared at incubation temperatures that reflected their environment of origin or at common incubator temperatures. Estimated growth rate and temperature sensitivity were also lower for ectomycorrhizal fugal isolates from Alaska. These pieces of evidence suggest that ectomycorrhizal fungi are thermally adapted to the thermal regime of their latitudes of origin. Presumably, this allows ectomycorrhizal fungi from different latitudes of origin to have similar carbon demands from their hosts. In contrast with the abilities of many plants and some ectomycorrhizal fungi, decomposer communities show very little acclimation ability over the course of a week. The ability of decomposer communities to acclimate may influence decomposition and soil carbon content. At different times during the year, however, decomposer communities were able to change their respiration as prevailing temperatures changed but not at all time points. This suggests that more than just temperature is important in affecting respiration at different times of year. Decomposer community structure, substrate availability, and moisture might potentially change at different times of year, all of which have the potential to affect respiration. In summary, my results suggest that soil microorganisms display some differences in metabolic response to temperature. Some ectomycorrhizal fungi acclimated their respiration while, for the most part, decomposer communities largely did not acclimate their respiration. In the one instance (May 2007) where decomposers significantly acclimated their respiration, the reduction in respiration across measurement temperatures was small in comparison with ectomycorrhizal fungi when they acclimated. Notably, the sensitivity to temperature by both ectomycorrhizal fungi and decomposer communities from the same red pine plantation in Pennsylvania was quite similar, which indicates that they might proportionally change their respiration rate in the same manner. When ectomycorrhizal fungi from Alaska and Pennsylvania were compared, our results indicate that their respiratory responses to temperature appear to be adapted to their thermal regime from their latitude of origin. The experiments in my dissertation highlight the facts that 1) much variability exists between different soil microorganisms in their metabolic response to temperature, 2) much variability also exists within a group of soil microorganisms (i.e. only 25% of ectomycorrhizal fungal isolates acclimated), and 3) different time scales can be quite important when examining metabolic responses to temperature.