Canopy Gaps Control Litter Decomposition and Nutrient Release in Subtropical Forests

Abstract

The formation of a canopy gap results in changes to the microenvironment which, in turn, affect litter decomposition and nutrient release. However, the mechanisms underlying these effects in differently sized gaps and non-gaps remain poorly understood. To address this gap in knowledge, we selected three large gaps (above 150 m2), three medium gaps (50–100 m2), three small gaps (30–50 m2), and three non-gaps with basically the same site conditions. We then used the litter bag method to investigate leaf and branch litter decomposition over a year in a Castanopsis kawakamii natural forest with the aim of characterizing the litter mass remaining and the nutrient release in canopy gaps and non-gaps. Our results revealed that the remaining litter mass of leaf and branch litter was lower in medium gaps compared to other gaps, and leaf litter decomposed faster than branch litter. Environmental factors were identified as the primary drivers of total carbon and nitrogen release during litter decomposition. Gap size (canopy openness), taxonomic Margalef index, the Brillouin index of soil microbes, soil total nitrogen content, soil pH value, and average air temperature were identified as the main factors driving carbon and nitrogen release from branch litter. In the late decomposition stage, the taxonomic Pielou index, soil total potassium content, soil water content, and average relative air humidity were the main drivers of nutrient release from branch litter. The soil water content and average relative air humidity were also found to be the main factors affecting the nutrient release from leaf litter throughout the different stages of decomposition. Overall, our study highlights the impact of canopy gaps on microenvironmental variation, taxonomic community diversity, and soil microbial functional diversity and how these factors ultimately influence litter decomposition and nutrient release. Our findings provide an important foundation for further research into soil nutrient cycling in subtropical natural forests.