Dynamics of pine ectomycorrhizae following root disturbance.

Ectomycorrhizae (ECM) and their hyphae may account for up to one-third of forest productivity, but we know little about their patterns of decomposition and recruitment. ECM decomposition rates are governed in part by the identity of the symbiont, while the species that colonize new fine roots are determined by a number of abiotic and biotic filters, including the developmental stage of the root system and hyphal network. Sections of forest floor humus were excised from mature pine stands (severing all roots), replaced and randomly sampled over time. Decomposing ECM and ECM forming on newly growing roots were tracked over 15 months by ITS sequencing. ECM were no longer observed on original roots 13 months post-disturbance, while ECM appeared on new roots after 10 months. Individually, the dominant ECM fell into three categories. 1) Cenococcum geophilum decomposed and recruited slowly, 2) Suillus spraguei and Russula spp. decomposed rapidly but exhibited minimal recruitment during the experiment, and 3) Clavulina coralloides and Lactifluus/Lactarius spp. degraded rapidly but also recruited rapidly onto new roots. Our results indicate that rates of ECM decomposition vary among fungal symbionts, and that root severing appears to shift the ECM community to a slightly earlier successional stage. The lack of recruitment of ECM formed by truly early-stage species is likely due to the low level of soil disturbance, which should be advantageous in the context of forest regeneration.