Combined effects of moss colonization and rock fragment cover on evaporation and water storage of shallow carbonate-derived laterite in karst mountainous lands

Moss cover and rock fragment cover are important factors influencing soil water dynamics in karst landscapes, but their mechanisms in regulating soil water in mountainous regions remain poorly understood. To address this knowledge gap, we conducted experimental trials in karst rocky desertification areas of southwest China. Using 27 soil flumes (50 × 30 × 10 cm), we simulated moss colonization (Racomitrium japonicum; seeding rate: 0.13 kg·m^–2) under varying rock fragment cover (0 %, 30 %, 60 %) to evaluate their combined effects on soil hydrology. Results demonstrated that moss establishment reduced evaporation by 48–72 % and increased water storage by 11–22 %, with synergistic gains driven by moss-rock interactions. Structural equation modeling revealed that rock fragments stabilized the microenvironment by increasing soil water content (standardized coefficient = + 0.59) and temperature (standardized coefficient = + 0.11), promoting moss growth. Moss colonization further suppressed evaporation (standardized coefficient = − 0.22) through surface sealing. These findings underscore the role of moss in decreasing evaporation losses and improving water retention in shallow karst soils, providing valuable insights for ecological restoration in karst rocky desertification areas.