Participating Students - Glenna Malcolm

Glenna M. Malcolm
Pennsylvania State University
Enrollment Year: 2002
Email Address: glenna.malcolm at gmail.com
Atmospheric Mentor: Kenneth Davis, The Pennsylvania State University
Biosphere Mentor: Roger Koide, The Pennsylvania State University

Research Topics
The goal of my research was 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 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 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 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.

Current Work

I currently employed as a half-time Post Doc Rsearcher in the Department of Plant Pathology at Penn State. I am investigating the interaction between different genotypes of a fungal pathogen, Verticillium dahliae, and their specificity or non-specificity for host (commercial crops) and non-host plants (often cover crops or rotational crops). This study system is quite interesting because V. dahliae has long-living fungal structures that can remain in the soil for up to 10 years and it causes significant vascular wilting to commercial crops worldwide. Further, the different genotypes of V. dahliae appear to be generalists (colonizing many host plants) and specialists (colonizing few host plants) and are differentially virulent on various crop plants. For all of the above reasons, management of vascular wilting caused by V. dahliae is quite complicated. By integrating information at the species level (genotype diversity) with ecologically-grounded questions, I hope to help in better management of this fungal pathogen. My specific questions are:

1) Do different genotypes of V. dahliae respond differently to root exudates from host and non-host plants?
2) Do different genotypes of V.dahliae differentially colonize the roots of host and non-host plants?
3) In the field, is there evidence for spatial separation of different genotypes of V. dahliae with particular genotypes colonizing host plants and others colonizing non-host plants?

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