A fundamental challenge in ecology is to understand the forces that both shape and maintain biodiversity at various spatial scales over time. Traditional microbial cosmopolitanism has asserted that due to microbes’ small size, high abundance, and other aspects of their biology, dispersal limitation is drastically reduced for populations of these organisms. However, recent studies suggest that there are biodiversity scaling rules common to all forms of life. Here, we aim to characterize the species-time-area relationship of prokaryotic communities under bioenergy crop (switchgrass) establishment at two ‘Dust Bowl’ remnant field sites (designated SL-silt loam and CL-clay loam) in Oklahoma that are low in nitrogen (N) and phosphorus (P) nutrient availability. We hypothesize that nutrient availability, along with the activation of beneficial plant-microbe interactions, will regulate microbial biodiversity scaling and that species turnover temporally will have a stronger effect on species number than area. Paired plots at each site, including a control fallow plot and a plot cultivated with switchgrass, were assessed by profiling (i) the spatial and temporal biodiversity scaling of bacterial communities using 16S rRNA high-throughput sequencing of samples taken from a cross design with increasing areas, and (ii) tracking the topsoil physiochemical properties over two complete growing seasons (17-months).
Results/Conclusions
We found that switchgrass significantly increased the total carbon (C) content at the SL site but not at the CL site when compared to the fallow plots. Soil nutrient heterogeneity was found to be higher at the CL site than at the SL site. The soil heterogeneity/turnover of the soil nutrient conditions across the different spatial scales was related to and helped in explaining the different patterns of species-time-area relationships observed for each plot. At both sites, species turnover was higher over time than with increasing area. Remarkably, the seasonal dynamics of the species-area relationship was positively related to the heterogeneity of soil P concentrations at both sites by multiple linear regression models. This linkage may reflect that the changes in P may influence the growth of the plants and thus mediate the soil nutrient conditions and plant-microbe interactions, which consequently will affect the overall bacterial diversity of the ecosystem. Together, our results stress the importance of nutrient condition and heterogeneity in regulating soil bacterial biodiversity at different scales and over time. Further investigations are underway to understand the net effect of switchgrass establishment on soil biodiversity scaling and differences in soil type to aid in sustainable switchgrass management practices.