Background/Question/Methods While often overlooked, diffuse trophic interactions among plants and their soil microbiomes can have large effects on aboveground plant traits as they regulate nutrients for plant uptake. For example, variation in bacterial richness within soil surrounding the roots (i.e., rhizosphere) can have selective effects on photosynthetic biomass. However, the extent of microbial selection on floral traits and phenology is currently unknown. Host specific microbial composition is dynamic and can be dependent on environmental and biotic interactions. Linking environmentally mediated shifts in microbial composition to changes in floral traits will give realistic insight on variation in plant productivity and how mutualisms respond to multiple selective agents. I used Lupinus neomexicanus and the seasonal North American Monsoons to test the following questions: (1) To what degree does microbial community structure associated with the rhizosphere covary with plant phenology, reproductive traits, and plant productivity? (2) How does seasonal monsoonal rainfall alter community structure of plant rhizospheres and contribute to variation in reproductive traits and plant productivity? To directly test to what extent rhizospheric microbial structure changes due to monsoon events, I added rainfall shelters which removed monsoon rainfall at 60% and 80% for a subset of plants (n=31 each). Abundance and richness of soil bacteria and arbuscular mycorrhizal fungal communities were quantified through 16S and 18S gene sequencing using the Illumina MiSeq workflow. Results/Conclusions I have sequenced the rhizosphere communities and recovered approximately 40,000 different bacterial sequences and ~500 different AM fungal sequences that have been used to determine community differences among rainfall shelter treatments. I ran a distance-based redundancy analysis and analysis of variance using the quantitative Jaccard distance between microbial communities and rainout shelter treatments. My analysis shows that bacterial and fungal community differ amongst treatments (p=6.9e-4, 5,000 model permutations). Overall, I predict that less diverse (reduced) microbiomes should lead to lower nutrient uptake affecting the expression of phenotypic traits. Accordingly, plants that receive fewer resources from the rhizosphere microbiome will have fewer flowers and higher reproductive cost. I anticipate strong directional shifts in plant life stages as a direct result of rain disturbance through the increased probability in recruiting novel microbes and thus observe community turnover between groups.
