Evidence of Plant-Soil Feedback in South Texas Grasslands Associated with Invasive Guinea Grass Independent of Soil Inoculation Method

Abstract Purpose: Plant-soil feedback plays a strong role in plant community composition, but the effect of invasive Guinea grass, Megathyrsus maximus, on these processes remains unexplored. Here, we aim to provide a first look at plant-soil feedback (PSF) process in South Texas savannahs currently undergoing invasion by Guinea grass. Our two main questions are (1) how does the presence of the invasive M. maximus alter PSF compared to non-invaded grasslands and (2) are these results robust to inoculation method. Methods: Under greenhouse conditions, we assessed growth of Guinea grass and response of the native seed bank in soil collected from grasslands invaded by Guinea grass and native grasslands using two methods of soil inoculation: individual and pooled soil samples. Results: Guinea grass grown in soil from invaded grasslands grew taller and accumulated higher biomass than in soil from non-invaded grasslands. Plants grown from the native seed bank were more species rich and abundant in soil from non-invaded grasslands but had higher biomass in soil from invaded grasslands. Overall, these results were robust to differences in inoculation method. Conclusion: In South Texas savannahs, presence of Guinea grass is associated with changes in the direction of plant-soil feedback processes with negative feedback processes possibly contributing to species coexistence in non-invaded native grasslands while positive feedback processes appear to reinforce invasion by Guinea grass. Future work is needed to assign causality of these changes to Guinea grass itself and further explore the role plant-soil feedback has in Guinea grass invasion.