Abstract:
Litter mass (LM) accumulation and subsequent decomposition affect soil organic matter (OM) content and atmospheric Carbon dioxide (CO2-C) emissions, influencing climate change. Despite the abundance of Mahogany mixed forests in wet and intermediate climatic zones in Sri Lanka, there are no comprehensive studies on soil CO2-C emissions and OM dynamics. This study aimed to assess the short-term impacts of LM on CO2-C emissions and OM% in a tropical Mahogany forest soil (MFS) at the Faculty of Agriculture, University of Ruhuna, Sri Lanka. Three pits (1 × 0.5 m2) were prepared at random sampling points and they were filled with grassland soil (GLS) to eliminate the effects of accumulated LM over time. Soil (0-10 cm depth) and LM sampling was done on nine days (1-2 weeks intervals) during March to August 2023. The CO2-C emissions and OM% were determined by NaOH-trapping and chromic acid wet oxidation (Walkley and Black) methods, respectively. The correlation analysis was done using the Microsoft Excel 2010 data analysis tool pack. The results revealed that initial OM% of GLS increased from 1.87% to 2.21%, approaching that of the original MFS (2.6%), suggesting enhanced soil carbon (C) stock. The OM% increased with LM up to 0.4 kg m⁻², then declined, while CO₂-C emissions showed the opposite trend, initially decreasing and then increasing at the same LM. The LM of 0.4 kg m-2 was a critical value (CV), which affected CO2-C emissions and OM% conversely. According to previous studies, the flavonoid compounds in Mahogany leaves inhibit microorganisms by forming complex compounds with microbial proteins. This can be a reason for the reduced CO2-C emissions and increased OM% with increasing LM up to a level of CV. With the succession of LM exceeding the CV, Mahogany litter decomposers could enhance their population growth and fresh OM inputs possibly generated priming effects, causing a disproportionate increase in CO2-C flux and net losses in soil C stock. Overall, the LM in a tropical MFS offered insights into the short-term OM dynamics, aiding assessments of forest floor contributions to climate change through CO2-C emissions.
