3150 Plant and Environmental Science
Email:  nteutsch_at_ucdavis.edu

 Hausmann CV

Arbuscular mycorrhizal fungi (AMF) are important plant root symbionts that improve plant nutrient uptake.  Despite their recognized importance, we poorly understand the factors controlling AMF community composition.  For my doctoral work, I explored how plant communities alter AMF abundance and composition in California grasslands.  I tested how (1) plant and AMF performance interact, (2) plant monocultures and mixtures determine AMF community composition, (3) plant phenology and neighbor identity alter AMF communities on a single plant host, and (4) plant phenology and neighbors affect AMF community composition on various plant hosts.  For these field and greenhouse studies, I employed a combination of morphological and molecular-based techniques to quantify and identify AMF.

First, I found that a single plant host alters the composition of AMF spores over time.  Moreover, host-specific AMF negatively impacted plant performance.  Second, I found that exotic annual grasses in monoculture harbor unique AMF communities, yet they represent incomplete subsets of AMF communities found in plant mixtures.  Additionally, I found identical AMF in two different plant communities despite differences in plant composition and life form.  Hence, complex plant communities can mask host effects due to other interacting factors that influence AMF community composition. 

Third, I found that the AMF community composition of a native perennial host shifted significantly when that host was established at various times with different annual grass neighbors.  Both plant phenology and neighbor identity interact to structure AMF communities at the seedling stage.  Finally, I found that annual grass hosts can harbor distinct AMF communities, but the composition of AMF communities depends on the interacting effects of host identity, timing of plant establishment, and neighbor identity.  The AMF communities of annual grasses were more plastic than those of a native perennial, perhaps demonstrating their more ruderal nature.

These studies elucidate how plant community complexity, phenology and host and neighbor identity determine AMF community structure.  Many of these factors interact strongly to create new assemblages of AMF.  These results improve our understanding of basic AMF community ecology and build a framework around which we can conceptualize the interacting factors that determine AMF community dominance and community composition. 

For my postdoctoral work, I am participating in a study that examines how tomato root gene expression responds to nutrient patches in the soil and whether those gene expression patterns are mediated by mycorrhizal fungi.  We have found that mycorrhizal colonization has a minimal effect on ammonium uptake and gene expression, but plants were highly responsive to the concentration of ammonium they encountered in the patch.  We are currently exploring how patterns of gene expression change when the plant roots encounter other nutrients as well.  Specifically, we are exploring the effects of phosphorus, zinc and their interactions on gene expression.