Context dependency of plant-soil feedback: How environmental conditions influence the relative abundance of mycorrhizal and pathogenic fungi

Background/Question/Methods

Plant soil feedback (PSF) can drive successional dynamics, maintain plant diversity and determine the success of exotic invaders. Meta-analyses have shown that effects of soil biota on plants are net-negative, indicating that detrimental impacts of pathogens often outweigh benefits from mutualists, such as arbuscular mycorrhizal fungi (AMF). PSF may depend on plant life history and provenance. Another factor that has received less attention is resource availability. High resource supply is predicted to reduce allocation to defense and to mutualists, which would favor pathogens, whereas resource-poor conditions ought to favor mutualists. While those predictions are theoretically sound, we have little empirical data outside controlled greenhouse experiments to assess their support. I will present results from surveys and experiments where we combined plant responses to soil biota with molecular characterization of fungal pathogen and AMF (mutualists) communities to assess if and how interactions change with soil fertility and moisture.

Results/Conclusions

We have seen consistent responses in PSF and fungal guilds across most experiments. Under ambient conditions, pathogen abundances were always greater than AMF, which is consistent with the general pattern of negative PSF. Pathogens tended to increase further with nutrient additions, whereas AMF were generally promoted by moderate drought or lower nutrient availability. We found remarkably consistent shifts in pathogen and mutualist ratios with nitrogen and phosphorus additions in Nutrient Network grasslands across four continents. This occurred despite substantial differences in fungal communities among grasslands, suggesting that responses are independent of compositions within guilds. In summary, our results indicate that resources can modify PSF in largely predictable ways.