Species composition influences soil nutrient depletion and plantphysiology in prairie agroenergy feedstocks

High-diversity mixtures of perennial tallgrass prairie vegetation could be useful biomass feed-stocks for marginal farmland in the Midwestern United States. These agroenergy crops can help meet cel-lulosic agrofuel targets while also enhancing other ecosystem services on the landscape. One proposedadvantage of high-diversity prairie biomass feedstocks is that they should become nutrient limited at aslower rate than monoculture feedstocks. In this study, we examine rates of soil nutrient depletion and thephysiology and performance of a focal species (switchgrass,Panicum virgatumL.) in four prairie agroen-ergy feedstocks with different species composition and diversity. The feedstocks in this study were a1-species switchgrass monoculture, a 5-species mixture of C4grasses, a 16-species mixture of C3and C4grasses, forbs, and legumes, and a 32-species mixture of C3and C4grasses, forbs, legumes, and sedges. Toassess feedstock effects on soil, we measured changes in soil N/P/K over afive-year period. We also per-formed a greenhouse study, in which we grew switchgrass plants infield soil conditioned by each feed-stock. To assess feedstock effects on plant function, we measured four physiological traits (photosyntheticrate, chlorophyll concentration, leafflorescence, leaf N concentration) on switchgrass plants within eachfeedstock in thefield. In the soil analysis, we found that the 5-species feedstock displayed higher rates ofsoil N/P/K depletion than other feedstocks. In the greenhouse analysis, we found that switchgrass plantsgrown in soil conditioned by the 5-species feedstock were smaller than plants grown in soil conditionedby other feedstocks. In the physiological analysis, we found that switchgrass plants in the 5-species feed-stock had lower leaf N, photosynthesis, chlorophyll concentration, and higherflorescence than switchgrassplants growing in other feedstocks. Collectively, our results show that prairie agroenergy feedstocks withdifferent species composition and diversity have different rates of soil nutrient depletion, which influencesthe physiology and performance of plants within the feedstock. These differences would ultimately impactthe ecosystem services (e.g., biomass production, need for fertilizer) that these prairie agroenergyfeedstocks provide