Root pathogen diversity and composition varies with climate in undisturbed grasslands, but less so in anthropogenically disturbed grasslands

Abstract

Soil-borne pathogens structure plant communities, shaping their diversity, and through these effects may mediate plant responses to climate change and disturbance. Little is known, however, about the environmental determinants of plant pathogen communities. Therefore, we explored the impact of climate gradients and anthropogenic disturbance on root-associated pathogens in grasslands. We examined the community structure of two pathogenic groups-fungal pathogens and oomycetes-in undisturbed and anthropogenically disturbed grasslands across a natural precipitation and temperature gradient in the Midwestern USA. In undisturbed grasslands, precipitation and temperature gradients were important predictors of pathogen community richness and composition. Oomycete richness increased with precipitation, while fungal pathogen richness depended on an interaction of precipitation and temperature, with precipitation increasing richness most with higher temperatures. Disturbance altered plant pathogen composition and precipitation and temperature had a reduced effect on pathogen richness and composition in disturbed grasslands. Because pathogens can mediate plant community diversity and structure, the sensitivity of pathogens to disturbance and climate suggests that degradation of the pathogen community may mediate loss, or limit restoration of, native plant diversity in disturbed grasslands, and may modify plant community response to climate change.

Fig. 1. Naturally occuring precipitation and temperature gradients across study sites.

Precipitation (a) and temperature (b) across our sampling sites. Remnant sites are indicated by filled circles, while disturbed sites are indicated by filled triangles. Sites are skewed vertically to avoid overlap to clarify where different sites are located. Color intensity represents rainfall (a) and temperature (b) intensity.

Fig. 2. Precipitation predicts fungal pathogen phylogenetic species richness in remnant grasslands.

GLM results showing mean annual precipitation prediction of phylogenetic species richness in fungal pathogens (a., remnant p = 0.06, b., disturbed p = 0.62). Points represent the raw data; the trendline is the predicted probability from the GLM.

Fig. 3. Precipitation and temperature interact to predict fungal pathogen phylogenetic species richness in remnant grasslands.

Soil fungal pathogen richness depends on the interaction between precipitation and temperature in remnant grasslands (Table 1b, p = 0.02). Pathogen phylogenetic species richness increases with precipitation at higher temperature, but decreases with precipitation at lower temperature.