Farner JE, Spear ER, Mordecai EA (2019) Soil type shapes unique pathogen communities on nearby populations of a California native bunchgrass. bioRxiv, 545632.
The role of infectious disease in regulating host populations is increasingly recognized, but the environmental conditions that facilitate versus hinder pathogen-mediated population regulation remain poorly understood. We compared the relative contributions of soil type and pathogen community composition to foliar disease burden in a perennial bunchgrass species found on two distinct soil types that support distinct plant communities in a California grassland. We hypothesized that populations on different soil types would have significantly different disease burdens caused by unique pathogen communities. To test this hypothesis, we compared foliar disease burden and foliar fungal pathogen communities in nearby populations of Stipa pulchra found in nonserpentine greenstone soil that is dominated by invasive Mediterranean grasses, and in serpentine soil, a harsh soil high in heavy metals and low in essential nutrients that supports a diverse community of native plant species. We analyzed the chemical makeup of serpentine and nonserpentine plant tissue to understand potential impacts of soil chemistry on plant health and pathogen community composition. We found that serpentine and nonserpentine S. pulchra experienced consistent, low disease pressure caused by distinct communities of foliar pathogens, and that serpentine plants, like the soil in which they grew, had elevated Ni and Mg content and decreased C, N, Ca, and P content compared to nonserpentine plants. The results imply that pathogens are unlikely to regulate the population dynamics of this native plant, and that pathogen communities are structured either by plant community composition or tissue chemistry. Local variation in soil type and annually variable conditions associated with high species turnover in pathogen communities may create a refuge from disease outbreaks for S. pulchra, contributing to the low disease burden observed on this and other Mediterranean grassland species. [link to publication in bioRxiv]