Revisiting the Nutritional Mode of Floccularia luteovirens: A Case for Facultative Saprobic Capacity

Floccularia luteovirens is a rare and edible fungus endemic to the Qinghai-Tibet Plateau. Traditional viewpoints have inferred it to be a mycorrhizal fungus based on its spatial association with Kobresia, yet direct morphological evidence (e.g., Hartig net) and molecular evidence is lacking. Through a systematic review of the existing literature, this study found that all current evidence supporting a mycorrhizal relationship is merely indirect inference. In contrast, experiments conducted by our research team demonstrated that this fungus colonizes well on sawdust-based substrates, which is compatible with saprobic growth capacity and does not exclude the possibility of conditional mycorrhizal symbiosis in natural environments. Based on these findings, we propose that F. luteovirens may adopt a facultative nutritional mode to adapt to the alpine environment. Genomic analysis revealed that the CAZyme repertoire of F. luteovirens (including key enzyme families such as GH6, GH7, and AA1) shows high similarity to that of the saprobic fungus Agaricus bisporus and appears to be more comprehensive than that of the ectomycorrhizal fungus Boletus edulis, based on current annotation data. This pattern suggests its potential capacity for lignocellulose degradation. The successful cultivation of its closely related species Lepista sordida on various lignocellulosic substrates further supports this functional potential. This study proposes that F. luteovirens employs a 'facultative nutrition' strategy, which presents an alternative perspective to the traditional view of obligate dependence on mycorrhizal symbiosis. These findings contribute to our understanding of fungal adaptation in alpine environments and may inform strategies for artificial domestication of this valuable species.