Influence of monsoon regime and microclimate on soil respiration in the tropical forests

The consequence of precipitation and how environmental factors influence soil respiration remain poorly understood in the tropical forest ecosystems under a monsoon climate in Malaysia. This study was conducted in a recovering tropical lowland Dipterocarpus forest in Peninsular Malaysia, and its monthly variations were examined in association with changing precipitation. Soil respiration was measured using a continuous open flow chamber system connected to a multi gas-handling unit and an infrared gas analyser. The aim of this study was to determine the effects of the monsoon period and microclimate of the tropical region on soil respiration. The average monthly soil respiration rates were 152.79 to 528.67, 120.97 to 500.73, 106.77 to 472.89, 122.89 to 453.89 and 120.33 to 434.89 mg m⁻² h⁻¹ in the respective months from September to January. The emission rate varied across the days and months, with the highest value recorded between September and October, and then gradually decreasing from November to January. Soil temperature explained more than 90% of the soil respiration rate whereas precipitation had a major effect during the monsoon regime. Soil organic carbon (SOC), total organic carbon (TOC), soil organic carbon stock (SOCstock), forest biomass, carbon to nitrogen ratio (C/N) and soil pH were found to vary in considerable amounts, provide nutrients and the environment favourable for microorganism activities, leading to emission of soil CO₂. The low values of soil respiration rate between November and January were due not only on the amount of soil moisture and water potential but also on the intensity and frequency of precipitation. Therefore, these results indicate that the monsoon regime can significantly alter the emission of soil CO₂ and influence the microclimatic conditions and other environmental factors

Soil carbon dioxide efflux and atmospheric impact in a 10-year-old Dipterocarpus recovering lowland tropical forest, Peninsular Malaysia

The recovering logged-over forest ecosystem increases the CO2 efflux into the atmospheric carbon pool in response to environmental factors to changes in the soil temperature and moisture. These CO2 outbursts can have a marked influence on the ecosystem carbon balance and thereby affect the atmospheric carbon pool. The study was conducted in the 10-year-old logged-over forest of Sungai Menyala forest, Port Dickson, Negeri Sembilan, Malaysia. The measurements of soil CO2 efflux were conducted using the continuous open flow chamber technique connected to a multi gas-handling unit and infrared CO2/H2O gas analyser. The aim of this study was to determine the soil CO2 efflux and the environmental variables and likewise the impact of environmental factors on soil CO2 efflux. Post-hoc comparisons were made using the Tukey test (p < 0.05), and multiple linear regression to determine the impact of environmental factors on soil CO2 efflux. Soil CO2 efflux ranged from 100.22-553.40 mg m-2 h-1 with the highest efflux in the afternoon attributed to an increase in soil temperature and low moisture. A higher soil temperature and low moisture signify an influential factor as the forest is recovering from logging activity. Furthermore, the predictor environmental variables: SOC (soil organic carbon), TOC (total organic carbon), SMC (soil moisture content), Bulk Density, SOCstock (soil organic carbon stock), TAGB (total above ground carbon biomass), Below Ground Carbon Biomass, soil pH, Nitrogen to Carbon ratio account for the spatial and temporal variation in soil CO2 efflux into the atmosphere. The analysis revealed a strong correlation between soil CO2 efflux, changes soil properties and environmental factors with an R2 more than 0.80 at p < 0.01. This is proven that logging activity accounts for the changes in environmental factors to influence soil CO2 efflux rate within 10-years of logging and forest recovering