Predictors of growth of ectomycorrhizal fungal mycelium vary with host (Pinus strobus) phenology

Ectomycorrhizal fungi (EcMF) are major contributors to belowground ecosystem production, yet our understanding of seasonal regulation of growth in EcMF is sparse. Both abiotic and biotic factors are likely to influence EcMF growth. We hypothesized that 1) soil temperature would predict mycelial growth, 2) soil moisture will be a good additional predictor of growth, and 3) host plant leaf expansion would reduce mycelial growth rates compared with non-expansion periods. At the Houghton Rhizotron we monitored EcMF growth on white pine roots at bi-weekly intervals for two years, using GIS-based change analysis to quantify mycelial growth. Growth was predicted by temperature over the entire year, including wintertime, when hyphae grew slowly through near-freezing soils. During leaf expansion period, temperature explained less variance in growth rates and the relationship had a lower slope. Soil moisture added little predictive power. This information can inform belowground carbon cycling models in pine forests.