Ventenata dubia is an invasive winter annual grass thriving in semi-arid grasslands decreasing biodiversity and pasture value. Studies have analyzed the effectiveness of traditional weed control methods like herbicides and burning on V. dubia suppression, however an understanding of the plant-soil feedbacks that may impact management of this invasive is lacking. Plant-soil feedbacks are changes in soil biotic and abiotic composition due to plant presence that may have positive or negative impacts on plant fitness. The purpose of this study was to determine the effect V. dubia invasion has on plant soil-feedbacks with native and nonnative species. To address this, we grew native and nonnative grasses (Poa secunda and V. dubia, respectively) in 4 soil types (soil from V. dubiainvaded sites, autoclaved soil from invaded sites, soil from non-invaded sites, and autoclaved soil from non-invaded sites) using a fully factorial experiment with 10 replicates. Plants were grown in the greenhouse for 5 months, after which roots and shoots were harvested and weighed. Soil was acquired from each treatment for nematode counts, nematode functional group sorting, and nutrient/elemental analysis. The effect of soil type on growth of native and nonnative grass species was analyzed using general linear models.
V. dubia invaded soils significantly reduced the fitness of both the invasive V. dubia and native P. secunda grasses and these negative plant soil feedbacks appear to be the result of non-species specific plant pathogens. Shoot mass was significantly lower in both grasses grown in invaded soils compared to non-invaded soils (p=0.032). The significantly larger increase in root mass after sterilization of invaded soils compared to non-invaded soils (p=0.035) is evidence that the negative feedbacks may be due to biotic as opposed to abiotic changes. V. dubia shoot mass showed a significant positive response to soil sterilization (p<0.0001) while native grass shoot mass only increased marginally. These results suggest that soil pathogens that negatively impact all plant fitness accumulate in the soil during a V. dubia invasion. V. dubia may also benefit to a greater degree than native plants from events that sterilize soil, like intense fire. This has important implications for selecting the most effective management approaches for V. dubia invasion.