BayCEER Workshop 2015

Redistribution of soil water by a saprotrophic fungus enhances carbon mineralization

P 3.2 in Droughts, floods and hidden flowpaths: This research holds WATER

Summer droughts are common in temperate forests and especially the upper soil horizons experience soil drought. Drought events can be accompanied by negative effects for forest ecosystems but many plants can reduce drought stress by hydraulic redistribution (HR). Similar processes were recently described for ectomycorrhizal networks but no information is available for saprotrophic fungi. They strongly contribute to belowground nutrient cycling, C and N mineralization.

We hypothesize that redistributed water by saprotrophic fungi triggers mineralization of organic matter in soils under drought conditions.

The impact of HR by saprotrophic fungi on mineralization was determined using mesocosms comprising two chambers, separated by a 2 mm air gap to prevent bulk flow of water. After inoculation with fungal cultures and a growth phase, both chambers were desiccated. Subsequently, only chamber I was rewetted while chamber II was treated with ¹³C labelled plant material. CO₂ samples were collected over 7 days after rewetting and analyzed for stable isotope ratio. In addition, enzymatic activity in chamber II was determined after 7 days. HR was prevented in the controls by cutting hyphal bridges between the two chambers.

HR led to a strong increase in volumetric water content in chamber II after rewetting of chamber I. The increase in soil moisture by HR strongly enhanced carbon mineralization and enzymatic activity in chamber II. Our results demonstrate that mycelia networks of saprotrophic fungi redistribut water from wet to dry soil. HR can partly compensate water deficiency if water is available in other zones of the mycelia network. It is likely a mechanism for higher drought resistance of soil fungi compared to bacteria.

Keywords: drought,carbon mineralization, fungi, hydraulic redistribution