Logging and forest conversion are occurring at alarming rates in the tropical forests of Southeast Asia. These disturbances alter soil physical, chemical and biological properties; and disrupt crucial ecosystem processes such as litter decomposition. Previous studies have linked soil microbial diversity to changes in edaphic properties such as pH, however the direct impacts of logging and forest conversion on microbial diversity are still poorly understood. Similarly, the links between microbial structure and ecosystem functions are not well understood. Here, we investigated the effects of disturbance created by logging and clear-cutting on soil physical, chemical and biological properties; and how changes in soil microbial diversity affect litter decomposition. We used top (5-cm) soil to assess soil physiochemical and microbial properties at five sites along a forest regeneration gradient in a tropical montane forest of Sabah, East Malaysia. Soil microbial diversity is estimated using next-generation DNA sequencing and standardized litterbags are used to assess litter decomposition rate and stabilization.
Results/Conclusions
Our results show strong effects of time since disturbance (TSD) on soil physiochemical and microbial properties. For example, soil pH and N increased with TSD; sulfur, C, percent sand, and soil organic matter increased with TSD at the younger sites, but began to decline at ~100 years post-disturbance. Bacterial and fungal diversity increased with TSD, however, fungal diversity began to decline at ~100 years. Soil pH was the strongest predictor of bacterial diversity, while percent forest cover was the strongest predictor of fungal diversity. Soil microbial diversity influenced litter stabilization and decomposition rate. Litter decomposition rate increased with fungal and bacterial diversity while litter stabilization increased with fungal diversity, and had a saturating relationship with bacterial diversity. Overall, soils of the oldest forested sites harbored significantly higher microbial diversity and stabilized greater amounts of litter. Our results suggest that logging and forest conversion significantly affect soil microbial diversity and consequently alter litter decomposition and stabilization in tropical montane forests. Our findings highlight the links between microbial structure and ecosystem function, and how these links are altered by human land use.