Extreme weather events, such as droughts, have a significant effect on crop productivity. Drought places stress on plants, making many physiological functions more difficult or even impossible. As such, drought threatens agriculture’s ability to keep up with the food demands of a burgeoning human population. Much research has been undertaken to determine how plants and plant communities respond to drought conditions, providing a good indication of how they might respond under future climate change scenarios.

Plant roots interact closely with the soil microbial community surrounding them. In some cases, plants can gain some resistance to the effects of drought conditions through their association with soil microbes. Therefore, understanding how soil microbial communities respond to drought conditions is vital to predicting plant responses, and could be key to developing techniques that minimise the negative impact of droughts on plants.

Of the soil microbes, the drought response of soil fungi is particularly poorly understood. Fungal community responses – such as abundance, species diversity and community composition – often contrast the responses measured for plant communities under the same conditions. The apparently contradictory drought responses of fungal communities highlight the urgent need for additional research.

Dr Ari Jumpponen at Kansas State University aims to bridge this knowledge gap by examining soil fungal communities under experimental chronic drought conditions. Published in Fungal Ecology in 2021, his research demonstrates the high variability in how soil fungal communities respond to drought.

Alongside colleagues at Kansas State University, the University of Massachusetts, and Colorado State University, Dr Jumpponen applied a combination of powerful techniques to examine soil fungi in an established field experiment.

The Extreme Drought in Grassland Experiment – or ‘EDGE’ – consists of six experimental grassland sites in central and southwestern USA. At these sites, rainout shelters passively reduce the amount of rainfall reaching the ground by approximately 66% during the April to September growing season. This equates to approximately 40% reduction in the total annual rainfall.

For their study, Dr Jumpponen and his colleagues used two of the six EDGE field sites, each containing ten replicated plots with rainfall shelters – to simulate drought – and ten replicated plots without rainfall shelters – to provide non-drought plots for comparison. They took soil cores from each plot and used them to characterise the soil fungal community.

Using a combination of pure culture-based and advanced molecular analyses, they measured three features of the soil fungal community: community composition, species richness and species diversity. Community composition identifies which groups of fungi are present, while species richness describes the number of species present. Finally, species diversity captures both species richness and the frequency at which each species is observed in a community.

Dr Jumpponen and his colleagues found that soil fungal communities did not change compositionally as a result of drought conditions. Largely similar groups of fungi were present in both the experimental drought and non-drought plots. Surprisingly, both species richness and species diversity increased as a result of drought conditions – but only at the wetter of the two EDGE field sites.

The findings indicate that fungal communities are compositionally-resistant to drought, but their species diversity may be more sensitive. Dr Jumpponen suggests that the ability to withstand drought conditions may be due to dormant life stages, such as spores that are not sensitive to environmental conditions.

The results also suggest that fungal communities accustomed to higher rainfall may be more sensitive to drought conditions. In contrast, fungal communities accustomed to drier conditions may already be adapted to surviving in drought conditions.

The responses of fungal communities directly contrast those of plant communities under similar conditions. While fungal communities from wetter areas appear more sensitive to droughts, plant communities from arid grasslands are often more sensitive to droughts. Dr Jumpponen points out that this means that findings from drought studies using plant communities are likely to be of little benefit to understanding fungal communities. This could be due to a key difference in the life histories of plants and fungi. Unlike plants, fungi have communities with a large number of species that can remain dormant for long periods to cope with unfavourable environmental conditions.

Separating fungal groups based on their life histories may also reveal key differences in their ability to adapt to drought conditions. For example, plant-associated fungi may be more sensitive to droughts because they experience the direct effects of the drought conditions as well as the indirect effects of changes in plant physiology and communities.

These conflicting results exemplify the complexity of building a complete understanding of how soil fungal communities will respond to drought conditions in different habitats and climates.

The team’s study highlights the importance of further research on the responses of fungal communities to environmental change. Dr Jumpponen points out that it is still unclear whether their results indicate drought-resistance in active fungal communities, or that the compositional-resistance to drought is due to dormant fungi waiting for favourable conditions before resuming activity. Fungal communities may be able to respond rapidly to changing environmental conditions because of their ability to remain dormant, which has implications for future climate change predictions.

Understanding how fungal drought responses interact with and influence plant communities, especially in relation to plant-associated fungi, is a key avenue of research with value for both agriculture and conservation.

Finally, Dr Jumpponen and his colleagues suggest that studies across larger areas and over longer time periods could reveal other important factors for fungal community responses to drought and other environmental conditions.