Endophytes Across the Plant Life Cycle: Potential Roles in Plant Protection, Litter Decomposition, and Nutrient Cycling.

Endophytes are diverse microorganisms inhabiting plant tissues that can promote plant growth, enhance stress tolerance, or suppress pathogens. However, the ecological roles of endophytes after host senescence and death remain poorly understood. This review examines how a subset of endophytes helps maintain ecosystem function in living plants, senescent tissues, litter, and associated microbial environments. Mechanisms of endophyte-mediated plant protection in living plants include pathogen inhibition, host regulation, nutrient acquisition, and abiotic stress tolerance. We also investigate post-senescence persistence and potential roles in litter decomposition and nutrient cycling via microbial and functional legacies, priority effects, extracellular enzyme activities, and community reassembly. Vertical transmission and horizontal dispersal can move microorganisms among stages, whereas host filtering acts after arrival to determine which microorganisms establish within host tissues. However, a full same-strain life-history loop has not been established. We propose an open, non-linear ecological continuum for selected endophytes that connects endophytic colonisation, saprotrophic persistence, and potential new-host establishment. In the future, longitudinal, strain-resolved, multi-omics, and synthetic-community studies will be conducted to verify the cross-stage connections and offer a microbial framework for plant protection, litter management, and ecological restoration.