Linking moss structural and functional traits to soil water fluxes and soil erosion

Mosses contribute to a multitude of ecosystem functions, and their structural and functional traits, such as shoot density or water storage capacity, can play an important role in performing these functions. It is widely known that mosses substantially reduce surface runoff and soil erosion, so the impact of mosses on soil hydrology is expected to be important worldwide. Nevertheless, it is poorly understood how moss species with different traits affect soil erosion and soil water fluxes. Therefore, this study aimed to assess the impact of the two moss species, Thuidium tamariscinum and Rhytidiadelphus loreus, on soil erosion, surface runoff, and water percolation and to investigate the influence of their structural traits. We conducted ex situ rainfall simulations with infiltration boxes that contain undisturbed topsoil samples. The two moss species differed significantly in their structural traits, with R. loreus showing longer shoots and branches, greater cushion height, and larger leaf area, while T. tamariscinum had a higher number of branches. Surprisingly, their water storage capacities were similar despite these morphological differences, suggesting a possible interplay of morphological features and trait resemblances, though the underlying mechanisms require further study. R. loreus and T. tamariscinum exhibited a comparable mitigating effect on sediment discharge and surface runoff, while moss cover had no significant influence on water percolation, regardless of species. Shoot density significantly correlates with reduced surface runoff, highlighting the key role of moss colony structure in hydrological processes.