 |
 |
David Myrold
Professor, Crop and Soil Science
|
 |
||||||||||||||
RESEARCH:
We study the microbiology of soil ecosystems and are particularly interested in the relationships between the structure of microbial communities and their activities. Our research ranges from process level studies of nitrogen and carbon cycling in soils, often using stable isotopes as research tools, to studies of the composition of microbial communities and the autecology of Frankia, using modern molecular methods.
Frankia are sporulating actinomycetes that form a nitrogen-fixing symbiosis with plants from more than 20 genera. This so-called actinorhizal association is analogous to the much better studied rhizobia-legume symbiosis. Unlike rhizobia, however, very little is known about Frankia, especially its ecology or genetics. Thus, there is a need for obtaining basic information about the population sizes and diversity of Frankia. There are also, however, a number of practical reasons for studying Frankia. Several actinorhizal plants in Oregon are present in forest and range ecosystems (e.g., red alder [Alnus rubra] and Ceanothus spp.). These actinorhizal associations fix nitrogen in amounts comparable to productive agricultural legume crops, and red alder is a commercially valuable timber species. Our research on Frankia uses DNA-based methods to study the ecology and diversity of this bacterial genus in soils. We were the first to use PCR-based methods to study the population dynamics of Frankia in soils. This work on Frankia that nodulate alders was broadened to include more recent studies of the Frankia that nodulate Ceanothus. These studies included investigations of the molecular phylogeny of the host plant and its bacterial symbiont using DNA sequencing and ecological studies on the diversity of Ceanothus-infective Frankia using a range of PCR-based methods.
More recently my laboratory has been involved in collaborative efforts to study the comosition of the entire soil bacterial community. We demonstrated the length-heterogenity PCR of DNA extracted from soils and fatty acid methyl ester (FAME) analysis of lipis extracted from soil provided similar resolving power in differentiating among microbial communities from different soils. We are actively engaged in an NSF-funded Micrbial Observatory, which has focused on determining the relationships between the diversity of functional genes of specific N cycling processes and the rates of these processes in soils. This work is being done in forest soils of the H. J. Andrews Long-term Ecological Research site. We are working to combine the use of stable isotopes and molecular methods to study the role of microbial communities in cycling C. In particular, we are following 13C-labeled plant material through various components of the soil microbial community using 13C-FAME analysis.
We also study the dynamics of nitrogen in the soil environment. These studies have been done in agricultural and forested soils. We have studied denitrification losses from several agricultural and forest soils. Many of these studies have used 15N stable isotope methodologies to investigate nitrogen cycle dynamics. Examples of past work include measuring nitrogen fixation rates and the dynamics of fixed nitrogen in alder forests and developing a new method to measure subsurface denitrification rates in situ. We are currently using 15N methods to study soil nitrogen transformations and the regulation of the nitrogen cycling at small spatial scales, such as soil aggregates and in the rhizosphere. A very interesting recent advance has been the use of time-of-flight mass spectrometry to study the assimilation of 13C and 15N by individual bacteria and fungi.