Principal Investigator - Brenda Casper

bcasper [at] sas [dot] upenn [dot] edu

UPenn Faculty Profile
NSF PIRE-Mongolia

Arbuscular mycorrhizal communities

    With the goal of understanding how soil types and host plant species influence the community structure of AM fungi, we have compared the AM fungal communities on the same host plant species (all C4 grasses) but in two very different soils—in tall grass prairie remnants at two sites in Iowa and in Eastern serpentine grasslands. Serpentine soils have elevated levels of Mg, relative to Ca, and other potentially toxic heavy metals (Cr, Ni) but are deficient in some important nutrients. In these systems, the taxonomic structure of AM fungal communities seems to be influenced much more by soil characteristics than by the identity of the host plant species. Further evidence of ecological matching between AM fungal communities and their soils comes from a greenhouse experiment in which we switched the fungal communities between the prairie and serpentine systems and found that plants grew better with native fungi. When the same AM fungal community is added to plants in the two different soils, the composition of the communities also diverges. These results suggest that some fungal species are better suited for serpentine while others are better suited for prairie soils and soil traits shape AM fungal communities. We also find evidence of functional variation within a single population of the fungal species Gigaspora gigantea. This is exciting as it suggests that some of the feedback we have detected between plants and their AM fungi may be due to intraspecific fungal variation.

    We are also exploring functional differences among co-occurring AM fungi with the idea of explaining why a single host plant normally harbors more than one fungal species. Previous studies have evaluated the benefit AM fungi provide to the host by comparing plant growth in response to a single AM species with plant growth when no fungi are present. Our unique approach to understanding the functions of different fungal species involves infecting the plant with several species simultaneously and then evaluating the effect on host plant growth when one of the species is omitted from the community. By repeating the experiment under different soil conditions we can determine whether the benefit provided by a particular AM species depends on soil composition. If so, this would be an example of niche partitioning among the fungi.

Research history

    Initially, my own interests (and graduate training) were in the area of pollination biology and plant breeding systems, which led me to studies related to the evolution of fixed embryo abortion and distyly, as a breeding system. I have also examined how soil nutrient heterogeneity changes rooting distributions of competing plants and investigated the consequences of soil heterogeneity for the size structure of plant populations. Thus, I feel comfortable supervising graduate research conducting research in diverse areas of plant ecology.