Seasonal fluctuation of autotrophic and heterotrophic soil respiration in the subtropical <i>Schima-Castanopsis</i> forest, central Nepal

Soil respiration, the carbon dioxide emitted by the biological activity of soil, is one of the primary ways of carbon release from forest ecosystems. Soil respiration can be partitioned into its two components: autotrophic respiration by roots (R<sub>A</sub>) and heterotrophic respiration by soil microorganisms (R<sub>H</sub>). This study aims to assess the seasonal fluctuations of R<sub>A</sub> and R<sub>H</sub> in the subtropical forest of Nepal dominated by <i>Schima wallichii</i> and <i>Castanopsis indica</i>. The trenching method (root exclusion method) was applied to partition R<sub>A</sub> and R<sub>H</sub>. The closed chamber method was applied to measure soil carbon emission. A Portable Infra-Red Gas Analyzer (IRGA) was used to measure CO<sub>2</sub> concentration in control and trenched chambers every month for one-year period. Soil temperature and soil water content were measured to analyze the effect of these environmental variables on soil respiration rate. The results revealed that the mean R<sub>A</sub> and R<sub>H</sub> were 116.1±10.61 and 130±6.9 mg CO<sub>2</sub>m<sup>-2</sup>h<sup>-1</sup>, respectively, with higher contribution (52%) of R<sub>H</sub> to total soil respiration. Significant seasonal variation with summer peak was remarkable in both components of soil respiration. R<sub>A</sub> and R<sub>H</sub> showed significant exponential relationships with soil temperature and soil water content. Soil temperature had a greater influence on R<sub>H</sub> than R<sub>A</sub>. Correspondingly, the temperature sensitivity of soil respiration (Q10) values of R<sub>A</sub> and R<sub>H</sub> were 3.218 and 2.083, respectively. This suggests that the soil CO<sub>2</sub> emissions in these subtropical forests may increase with future climate warming with more temperature sensitivity of autotrophic respiration.