The effects of a changing environment on fungal symbiont communities

Background/Question/Methods

Factors such as climate, physical and chemical environment, and biotic interactions have long been recognized as highly influential on the structure and function of terrestrial plant communities. Changes in the environment have directly and indirectly affected plant growth, fitness, and physiological processes, therefore altering ecosystems. Shifts in environmental conditions not only affect plant communities, but also fungal symbiont communities associated with plants. These ubiquitous symbionts, ranging from mutualists to pathogens, are highly important players in ecosystem processes: they can affect plant competition, provide protection from herbivores and other microbes, and facilitate the uptake of nutrients.  Despite their widespread occurrence and potential ecological importance, there is an extremely limited understanding of the factors influencing fungal symbiont communities. In a changing environment there is need to understand the response of fungal symbionts within these communities and how they might differ from plant responses. To investigate the effects of environmental change on fungal communities, I sampled fungal symbionts from perennial prairie plants within two existing experiments manipulating CO₂, nutrients, herbivore presence, temperature, precipitation, and host community composition. I then characterized fungal diversity and composition by morphotyping and sequencing the resulting fungal isolates.

Results/Conclusions

Fungal symbionts were isolated from every plant species sampled (4009 isolates from 566 host plants), confirming their ubiquity in grassland ecosystems. Host identity was found to be a strong determinant of symbiont diversity and abundance: on average, legumes harbored the greatest abundance of fungal symbionts, followed by forbs, and then grasses. Effects of elevated CO₂, increased temperatures, and decreased water availability on fungal symbiont communities varied widely across specific host plant species. Decreased water availability was associated with a lower abundance of fungi in the C3 grass Poa pratensis, but a higher abundance in the C4 grass Andropogon gerardii. Decreased water availability had a similar effect to P. pratensis on fungal abundance in the forb Solidago rigida. However, when N fertilizer was added under water-stressed conditions, fungal abundance in S. rigida increased. Fertilization had no significant effect on the species richness of fungal symbionts in grasses. When herbivores were excluded from the experimental plots, fungal species richness in grasses drastically decreased. These results suggest a strong role for environmental changes at multiple scales in determining the diversity and structure of fungal symbiont communities.