Seasonal dynamics of the ectomycorrhizal fungus Lactarius vinosus are altered by changes in soil moisture and temperature

Ectomycorrhizal fungi are important components of the carbon and nitrogen cycles in forest soils and improve the nutrient uptake of many plants. There have been few assessments of how soil fungal biomass is affected by climate; however, a good understanding of how soil mycelium is correlated with climate is essential to predict long-term responses to global warming. Soil extramatrical mycelia (EMM) of Lactarius vinosus, a highly valued and edible ectomycorrhizal species, was quantified by performing qPCR analyses of soil samples that were collected monthly from 28 long-term experimental plots. The belowground moisture and temperature of these plots were individually recorded every 2 h. L. vinosus soil EMM biomass fluctuated between 44 and 261 kg ha−1, with the maximum biomass occurring during spring months and the minimum occurring during winter and summer months. Mean mycelial turnover was estimated to occur 7.0 times year−1. Soil EMM was reduced under low soil temperatures and when there was a combination of high soil temperatures and low soil moisture, most likely caused by reduced C allocation from the host under both winter and summer conditions. Preliminary models using simulated reductions in soil moisture and increases in soil temperature showed that soil EMM increased significantly during winter–spring months, whereas EMM decreased significantly during summer months. These results suggest that warmer conditions would lengthen the period of L. vinosus biological activity during winter months, whereas increasing periods of drought would prevent the growth of this species during summer months. Our study shows significant soil EMM seasonality and highlights potential climate-driven annual cycle shifts of soil mycelia.