The desiccation of upper soil horizons is a common phenomenon leading to a general decrease in microbial activity. Yet, fungi are often better adapted to soil desiccation than bacteria. One reason for the better adaptation to desiccation may be hydraulic redistribution (HR) by mycelia networks of water from moist to dry soil areas along water potential gradients. We hypothesized that HR triggers carbon (C) mineralization in dry soils and impacts nitrogen (N) translocation within mycelia networks. Further, we hypothesized that the HR and its impact differs among mycelia network organizations.
Material and Methods
We studied HR in the non-differentiated mycelium of Agaricus bisporus and in the mycelial cord forming species Schizophyllum commune and compared it to capillary water transport. Experiments were conducted in mesocosm with a hydraulic barrier between a dry and a wet soil compartment using deuterium labelled water and labelled (13C, 15N) plant material.
A. bisporus and S. commune redistributed water at a flow velocity of about 0.3 and 0.43 cm min-1 per hyphae, respectively, indicating a stimulation of HR by mycelial cords. The amount of transferred water was similar to capillary transport in a sandy soil and resulted in a water potential increase of the bulk soil. While HR by A. bisporus strongly enhanced C mineralization by up to 2800% in the dry soil, HR by S. commune only slightly increased C mineralization within 7 d. In addition, S. commune translocated N towards the plant material for hyphal growth thereon, whereas A. bisporus translocated N within the mycelial network towards the wet soil.
Saprotrophic fungi have the potential for HR and to overcome hydraulic barriers between dry and wet soil compartments. The impact of fungal HR on C mineralization and N translocation in dry soils is potentially very high but sems to be species specific and related to the resource usage.