All plants harbor diverse microorganisms, including endophytic fungi living inside plants without causing apparent symptoms. Although mosses are present in all terrestrial environments and represent one of the earliest plant lineages adapted to terrestrial life, their interactions with fungi are often overlooked. By establishing a co-culture experiment using a broom moss (Dicranum scoparium) and its associated fungi, we demonstrated 1) fungal trophic modes can change according to the host senescence level; 2) most fungal endophytes have a neutral or promoting effect on moss growth. Our study suggests that the trophic states of many fungi might be fluid. We also showed the beneficial effect of moss-endophytes, pointing to future research questions and potential applications.