Subtropical forest floor CO emission at the Kaziranga National Park in Northeast India.

This study investigates the seasonal and diurnal variations of soil CO flux (Fc) and the impact of meteorological variables on its dynamics. The study took place in the subtropical forest ecosystem of Kaziranga National Park (KNP), from November 2019 to March 2020. The highest Fc (6.24 gC m day) was observed in the pre-monsoon season (March), and the lowest (0.85 gC m day) in winter (February), with the mean value of 2.19 ± 0.84 gC m day. Fc is primarily influenced by changes in air temperature (Tair), soil temperature (Tsoil), solar radiation (Rg), vapor pressure deficit (VPD), and photosynthetically active radiation (PAR). This is evident from the strong positive correlations of Fc with Tair, Tsoil, Rg, VPD, and PAR (correlation coefficients being 0.75, 0.67, 0.37, 0.59, and 0.37, respectively; all significant at 99% level) indicating their critical role in driving soil respiration. Conversely, relative humidity (RH) and atmospheric pressure (Pair) negatively affect Fc. Soil moisture (SoilM) influenced Fc to some extent, but its effect was less pronounced compared to Tair, Tsoil, and Rg. Diurnal variations revealed higher Fc during the daytime (between 10:00 and 14:00 IST) and the lowest in the night-time (between 05:30 and 07:00 IST). These findings underline the strong seasonal and diurnal controls of environmental factors on soil respiration enhancing our understanding of carbon dynamics in subtropical forest ecosystems.