Soil contains the largest diversity of all terrestrial ecosystems, especially microorganisms and mesofauna. However, this diversity is poorly quantified, and its relationship to ecosystem functioning is not well understood. Here, we propose to examine the relationships between the diversity and activities of soil microorganisms and stability of soil biological systems. Stability of soil biosystems will be measured by assessing activities of two plant pathogenic fungi, Pythium ultimum and Rhizoctonia solani. Three major questions guide this research: 1) Does diversity of soil microorganisms and mesofauna increase as intensity and frequency of disturbance decrease and resource availability increases in alternative agroecosystems? 2) Do high activities and diversity of soil microorganisms and mesofauna reduce activities of root pathogens? 3) Does the increase of diversity and activities of soil microorganisms and mesofauna enhance the resistance of soil biosystems to introduced pathogens? To expand the generality of findings, experiments will be carried out in two settings, one in soils of five adjacent ecosystems along the disturbance gradient, and another in four different types of soils. This study will advance our understanding of the relationship between soil diversity and the stability of soil biosystems. Since soilborne plant pathogens often cause extensive damage to many crops, knowledge of the effects of soil microorganisms on plant pathogens will also help us design better practices that reduce crop damage caused by these pathogens in sustainable agriculture.
A major uncertainty in predicting long-term ecosystem C balance is whether stimulation of net primary production will be sustained in future atmospheric CO 2 scenarios. Immobilization of nutrients (N in particular) in plant biomass and soil organic matter (SOM) provides negative feedback to plant growth and may lead to progressive N limitation of plant response to CO 2 enrichment. Soil microbes mediate N availability to plants by controlling litter decomposition and N transformations as well as dominating biological N fixation. One critical question is whether CO 2-induced N accumulation in plant biomass and SOM will result in N limitation of microbes and subsequently cause them to obtain N from alternative sources. Our current project examines
Arbuscular mycorrhizal (AM) fungi are ubiquitous in terrestrial plant communities, which significantly impact plant nutrient acquisition and community composition. Many cool-season grasses also form symbiosis with fungal endophytes that often enhance host resistance to herbivores, pathogens and other environmental stresses such as drought. Sporadic data suggest that there may be either competition for carbon resources within the host between the endophytes and mycorrhizae or that endophytes are inhibiting AM colonization through fungitoxic compounds. However, direct convincing evidence is still lacking. Our current project examines 1) how mycorrhizae and endophytes influence plant acquisition of N and other nutrients, and 2) whether endophytic fungi compete with mycorrhizae for C sources in their hosts, and inhibit the infection and activities of mycorrhizae.