Drought has short-term effects on soil fungal communities leading to long-term effects on soil functions

Climate change increases the magnitude and length of drought periods. Drought has direct and indirect effects on soil fungi and functions they provide. Here, we conducted a mesocosm experiment with four soil inocula representing gradient in levels of fungal biomass to study effects of drought on soil communities and functions. In a fully factorial design, half of the mesocosms were subjected to severe summer drought while half served as irrigated controls. Fungal biomass and community structure were monitored throughout first year after drought. Concomitantly, soil (multi)functionality was measured by plant yields, number of pests and other organisms, respiration, and decomposition. We show that drought has a direct negative effect on soil fungal biomass and diversity and that the magnitude of the effect depends on the initial community in soils. Furthermore, communities change in response to drought with observed decrease in network connectivity and changes in dominant taxa. While the effect of drought on soil fungal community and biomass gets smaller in time since drought, the functional legacy of the drought remains – potentially due to permanent changes in keystone fungal taxa. Particularly, the effects of drought legacy are apparent as reduction of crop yield in recovery period and slower decomposition rate 6 months after the drought. The effect on yield is however, soil inoculum dependent. Furthermore, the legacy effects of drought on fungal communities in bulk soil are smaller as compared to the effects on rhizosphere soil. We conclude that drought has unexpected long-term legacy effects on soil functions and that this effect is amplified in the rhizosphere. We further show that effects of drought depend on initial soil communities and that more diverse and fungal-rich communities recover faster from the drought. We conclude that watering of soils can alleviate the most acute drought stress affecting soil fungal communities and hence improve long-term functionality of the soil.