Fungi from land to sea: phenotypic plasticity drives functional adaptation across saline and non-saline habitats

Fungi are highly efficient degraders of organic matter, including recalcitrant compounds, and are therefore key recyclers in global biogeochemical cycles. While the vast majority of fungal diversity has been studied in terrestrial environments, marine fungi remain largely underexplored despite their ecological relevance and growing biotechnological interest. Notably, only ~1% of described fungal species originate from marine environments, and many of these are also found on land, raising the question of whether environmental adaptability is driven by species-level traits or by strain-level plasticity.

To address this, we compared worldwide strains of the same fungal species isolated from terrestrial and marine environments, integrating genomic analyses with detailed phenotypic assays. Our study focused primarily on the genus Trichoderma, a taxa with key roles in decomposition, plant-fungus interactions, and industrial enzyme production, including the cellulase-producing workhorse Trichoderma reesei, which served as key reference system.

While genome content was largely conserved across strains, pronounced phenotypic divergence was observed between marine and terrestrial isolates regarding salinity tolerance, and divergent metabolic niches through distinct carbon source preferences and altered rhizosphere interactions, even under saline conditions. These results suggest that environmental adaptation in Trichoderma is primarily driven by physiological plasticity rather than major genomic restructuring, indicating a broad physiological reaction norm that allows for the colonization of diverse saline and non-saline habitats.

Our findings highlight marine fungi as overlooked reservoirs of adaptive traits relevant to biogeochemical processes and biotechnology, including enzyme production, metabolite diversity, and stress-resilient plant–fungus interactions. By linking ecological origin to phenotypic performance, this study underscores the evolutionary plasticity of marine fungi and their potential role in shaping resilient bioprocesses and ecosystem functioning in a changing planet.