Cassie Ettinger, Ph.D.

While the rhizosphere is one of the most diverse terrestrial ecosystems and directly influences the cycling of nutrients within an ecosystem, relatively little is known about microbial community assembly and how plant species identify and interact with microbial species pools to determine the composition and abundance of the rhizosphere soil community.

I am collaborating with Dr. Marina LaForgia, to study how below-ground plant-microbe feedback loops during competition between native wildflowers and invasive grass species in California grasslands across varying precipitation regimes. This study involves a field experiment which uses metagenomic sequencing to assess microbial community assembly and function during competition between communities of invasive grasses and native wildflowers grown in combination under varying precipitation regimes. It also involves a greenhouse experiment which uses high throughput sequencing of the 16S rRNA gene and internal transcribed spacer (ITS) regions to look at the rhizosphere communities of each grass / wildflower species when grown alone as well as in pair-wise combinations.

In our greenhouse study, we found that the bacterial alpha and beta diversity differed between native forbs and invasive grasses, but that fungal alpha and beta diversity did not. We also found that bacterial beta diversity during competition was distinct from individual plant bacterial beta diversity. We also identified five bacterial families that varied in normalized abundance during competition and that were correlated with plant biomass under competition. We speculate that invasive grass dominance over these natives may be partially due to effects on the rhizosphere community, with changes in specific bacterial families potentially benefiting invaders at the expense of natives.