LB 24-206 - Untangling Biotic and Abiotic Factors that Structure Prairie Pimple Mound Plant Communities

Although many studies suggest that plant community composition is a result of competition for soil nutrients, others have shown that root-associated symbionts also regulate plant communities through plant-soil feedbacks. Few studies, however, have been designed to test the relative contribution of these two regulatory mechanisms to plant community assembly. Prairie pimple mounds (relict nebkhas) provide an ideal system to study how below-ground biotic and abiotic factors interact to affect plant communities, in part because they exhibit distinct environmental changes over small spatial scales. In this study, we 1) characterized the spatial change in plant community composition across twenty paired pimple mound and surrounding prairie matrix sites, 2) characterized spatial variation in soil abiotic properties across these same sites, and 3) conducted a greenhouse experiment that tested the relative contributions of abiotic and biotic soil factors to the growth and survival of eight plant species common to either pimple mounds or the prairie matrix.We found strong evidence that both plant communities and soil abiotic properties differed between pimple mounds and the surrounding prairie matrix. For example, pimple mounds had six times the available phosphorus than the prairie matrix. Collectively, nutrient compositions of mound soil were more similar to other mounds than they were to adjacent matrix plots (R = 0.434, P < 0.001). Likewise, mound plant communities of pimple mounds were more similar to other mounds than they were to the adjacent matrix plots and vice versa (R = 0.787, P < 0.001). We also found that plots that were more similar in plant community composition tended to have more similar soil nutrient compositions (Mantel statistic R = 0.5147, P < 0.001). In our greenhouse study, the eight common prairie plant species were planted separately in pots containing either sterilized pimple mound or prairie matrix soil, inoculated with either soil microbial communities from live pimple mound or prairie matrix soil to measure the effect on plant biomass. Preliminary results show a significant effect of soil type and inoculum type on above ground biomass (soil: F1, 269 = 267.24, P < 0.001, inoculum: F1, 269 = 14.25, P < 0.001), as well as significant interactions between species identify, soil type (F7, 269 = 4.51, P < 0.001), and inoculum type (F7, 269 = 3.86, P < 0.001). Collectively, these results indicate that both abiotic and biotic soil factors are important in generating spatial variation in plant communities.