Mutabilis in mutabili: Spatiotemporal dynamics of a truffle colony in soil

Abstract

The functioning of ectomycorrhizal (ECM) symbioses is closely related to the development of the soil mycelial phase the ECM fungi. The properties and spatiotemporal dynamics of such mycelia in ecosystems is, however, poorly understood. Here we show, using a soil colony of summer truffle (Tuber aestivum) as a model, that an ECM mycelium may only grow and colonize newly-opened soil patches when soil temperatures rise above certain threshold, in this case +10 °C, provided other requirements such as sufficient soil moisture are fulfilled. Extension rates of truffle mycelium in the fields was recorded as >0.3 μm min−1, several-fold greater than that predicted from laboratory cultures. Further, we demonstrated that there was a consistent spatial differentiation in mycelium growth patterns within the fungal colony on a decimeter scale, changing from “diffusion” type of growth at the colony margin to “colony-front” pattern further away from the colony margin. This change was clearly accompanied by shifting structure of soil microbial communities with Terrimonas sp. and another unidentified bacterium correlating with the “colony-front” mycelium growth pattern, and Sphingomonas sp. and Lysobacter brunnescens with the “diffusion” type of mycelium growth. Possible implications of the observed truffle colony differentiation are discussed for processes like fruit-body formation and dispersal of this ECM fungus. Our data indicate that the thallus of T. aestivum has to be considered as a principally variable (“mutabilis”) being in space and time, whose behavior correlates with conditions in ever changing soil environment (“in mutabili”).