Temperature determines the biomass of forest floor bryophytes: A cross-regional investigation in 413 sites

Understory bryophytes play unique and disproportionately important roles in water retention, biogeochemical cycling, and biodiversity conservation, and serve as bioindicators of environmental health in forest ecosystems. However, biogeographical research on the biomass of forest bryophytes is inadequately studied and has been limited to elevational gradients. We conducted a systematic cross-regional survey of bryophyte biomass across 413 forest sites in Sichuan province, China. We analyzed how each environmental variable, including climatic and atmospheric factors, overstory covers, and soil nutrients, relates to bryophyte biomass and quantified their relative contributions. The results indicate that, largely similar to previous local investigations and experiments, at a large scale, bryophytes are abundant in forests with lower temperature, nitrogen deposition, vapor pressure deficit (VPD), and tree and herb covers, as well as higher light availability. Moreover, bryophyte biomass is positively associated with soil carbon and nitrogen content. These environmental variables are closely related and jointly influence bryophyte biomass, with mean annual temperature (MAT) being the most significant factor (accounting for 83% of the relative contribution). The biogeographical patterns of bryophyte biomass contribute to deepening our understanding of their adaptations to multiple environmental variables and enable us to predict their responses to global climate change. These patterns also provide essential evidence for establishing more accurate terrestrial vegetation ecosystem models.