Fine root endophytes forming winter mycorrhiza

Arbuscular mycorrhizal fungi, classified in the subphylum Glomeromycotina, are obligate symbionts that depend on photosynthetic products from plants. There is substantial evidence that AMF support plant and crop growth in natural and agricultural ecosystems. Fine root endophytes (FRE) also co-occur in plant roots with AMF in all but tropical environments. However, their presence remains poorly recognised, and their lifestyle and functionality remain largely unknown. Our analysis demonstrates that, in contrast to AMF, FRE colonise plants during the winter season, when photosynthesis is more challenging. It is also noteworthy that FRE was unable to colonise the roots of spring-sown crops. The results of our laboratory pot experiments demonstrated that low temperatures are not sufficient for FRE colonisation. Furthermore, we observed that FRE, in contrast to AMF, exhibited increased colonisation in soils containing metabolically inactive plants. Our results suggest that FRE does not contribute to the increase of ecosystem biomass through direct photosynthesis in summer, but may play an overlooked role in the formation of mycorrhiza-based soil ecosystems in winter. However, this winter ecosystem can be disrupted by conventional bare fallow management of the field, interrupting the annual cycle.