Respiration activity of ectomycorrhizas from Cenococcum geophilum and Lactarius sp in relation to soil water potential in five beech forests

Forest trees are involved in root symbioses with hundreds of species of ectomycorrhizal fungi which constitute functional guilds able to improve the water and mineral nutrition of host trees. In temperate ecosystems, water shortage is a main factor limiting tree vitality. To assess how soil water conditions affected the physiological state of beech (Fagus silvatica L.) ectomycorrhizal roots, we monitored glucose respiration of two ectomycorrhizal types (Lactarius sp. and Cenococcum geophilum) during two complete growing seasons. Five stands of contrasting soil conditions were chosen in north-eastern France. The top soil horizons were equipped with micropsychrometers for measuring water potential and temperature. Glucose respiration on individual ectomycorrhizas was measured in vitro by trapping [C-14]-CO2 from radiolabelled glucose. For soil water potential < -0.2 MPa, the potential respiration activity of C. geophilum ectomycorrhizas was significantly less altered than that of Lactarius sp. ectomycorrhizas, indicating that C. geophilum is more likely than Lactarius sp. to maintain the physiological integrity of beech roots facing drought stress.