COS 153-6 - Influence of annual grass invasion on biocrusts and mycorrhizal inoculation potential in a semi-arid grassland

Abstract: Networks of mycorrhizal fungi may facilitate the distribution of growth-limiting resources (e.g. nitrogen, water) from biological soil crusts (biocrusts) to plant roots in semiarid grassland soils. Biocrust cover has decreased with invasion by the winter annual grass, Ventenata dubia, however, invasion by V. dubia has unknown effects on arbuscular mycorrhizal (AM) fungi. In a field survey and a glasshouse experiment, we investigated how biocrust microsites influence the inoculation potential of AM fungi during V. dubia invasion. At three sites across an endangered semiarid grassland, we established replicate field plots that were categorized based on cover of native and invasive plant species. The native plot category had >70% native plant species cover, transition plots contained a mixture of native and invasive plant cover, and invaded plots had >90% invasive V. dubia cover and surveyed the percent cover of biocrusts and plant species in each plot. To determine if biocrusts were associated with higher abundance of AM fungi, and to evaluate how invasion impacts AM fungal inoculation potential in soil, we collected soil samples from below biocrusts and bare soil. We collected all samples 10cm away from two focal plant species, the dominant native perennial bunchgrass Pseudoroegneria spicata and the invasive grass V. dubia. Soil samples from each plot were used as inocula in a mycorrhizal inoculation potential experiment and plants were grown in a greenhouse for six weeks, and after harvest, percent fungal colonization was quantified in roots.

Preliminary results indicate that the invasive annual grass V. dubia did not impact the inoculation potential of AM fungi in the sites sampled, suggesting that there may be latency between shifts in the plant community (e.g., native plants replaced by V. dubia), and mycorrhizal inoculation potential in invaded soil. However, the soil beneath biocrusts in native plots had higher mycorrhizal inoculation potential compared to bare soil in native plots, transition plots, and invaded plots at one of the three sites. Percent cover of biocrusts was also higher in native plots compared to transition and invaded plots. Results from our study suggest that restoration management practices that prioritize biocrust inoculation following invasion by V. dubia may improve native plant establishment by improving nutrient and water pools available for uptake by arbuscular mycorrhizal fungi. A better understanding of the interactions among native plants, biocrusts and AM fungi will be important for mitigating the impacts of invasive species and for informing grassland restorations.