Fungal Partnerships in Plant Roots Shape Competition and Coexistence

The Science

Most plants form symbiotic relationships in their roots with microscopic fungi. These partnerships are known as mycorrhizal symbiosis. Scientists have long known that the exchange of sugar for nutrients between individual plants and fungi is mutually beneficial. However, they did not know how the diversity of the specific mycorrhizal partnerships found in nature affects competition among different plant species. This research demonstrates that the presence of host specific fungi can determine winners and losers in plant competition. Surprisingly, however, these fungi can also help multiple plant species to coexist by letting them access different nutrient pools.

The Impact

This research provides a new perspective on what controls the distribution and abundance of plants in an ecosystem. Previous work has focused primarily on environmental conditions such as light, water, and nutrients as factors determining the mix of plants in an ecosystem. The current study changes existing ecological understanding by showing that the type of microbial symbionts in a given soil can also determine plant species composition. The finding highlights the importance of understanding what controls the composition of microbes in soils. This knowledge applies to both natural and human managed ecosystems. It can therefore help scientists design new microbial tools to aid agriculture, forestry, or ecosystem restoration.

Summary

Most plants form partnerships with a diverse cast of mycorrhizal fungi in their roots. While many of these mycorrhizal fungi can be partners with more than one plant species, there are a few dominant types of mycorrhizal association that are host specific. The two most common associations are known as ectomycorrhizal symbiosis and arbuscular mycorrhizal symbiosis. In this study, researchers used one arbuscular and one ectomycorrhizal plant species, manipulated the presence of their fungal partners, and measured how this change affected plant growth. The researchers also used new developments in ecological theory to predict whether both plant species would coexist stably, coexist unstably, or whether one species would exclude the other.

Changing the combination of mycorrhizal fungi present in an ecosystem fundamentally altered the researchers' predictions about competition, creating outcomes ranging from competitive exclusion to stable coexistence. While both arbuscular and ectomycorrhizal fungi improved the growth and competitiveness of their host plants, the study also found that the presence of these fungi altered the amount and source of soil nutrients each plant took up. This form of niche differentiation was strong enough to allow the plant species to coexist when both fungal symbionts were present. These results indicate the need to include microbes in a holistic framework of plant competition.

Funding

This work was funded by the Department of Energy Office of Science, Biological & Environmental Research program and by a Faculty Early Career Award from the National Science Foundation.