The predicted increasing atmospheric carbon dioxide (CO2) level is responsive to altering the future climate, and a small change in the soil carbon may significantly affect the forest carbon cycle and climate system. Soil respiration (SR) and its influencing factors like soil temperature (ST), soil water content (SWC) and surface litter-fall were measured monthly over one year in a sub-tropical Pine (Pinus roxburghii) forest of Bhaktapur district located in central Nepal to determine the SR of the forest and, its variations and sensitivity. The results showed that SR varied to the changes in ST by an exponential significant positive correlation between them. The optimum SR was observed between 10 and 22ºC, and the highest SR were obtained above ST at 20ºC. The temperature sensitivity value of SR (Q10) was estimated at Q10 = 2.13. The significant exponential curve represented the effect of SWC on SR. The higher SR rate was mostly measured between 10 and 25% SWC. The monthly and seasonal variations of the SR rate were consistent with the ST, SWC and litter-fall variations. The study showed that the combined effect of temperature and precipitation might be the major cause of SR variations; however, ST is adequate for increasing SR. Hence, the warming further enhances carbon emission from the forest floor and inversely increases carbon to contribute to climatic change through this pine-dominated forest stand structure.

Temperate forests are considered most fragile hence need to recognize their vulnerability owing to continuous climatic changes and anthropogenic activities. In this study, we assessed soil respiration (SR) by using the chamber method in a natural Rhododendron (Rhododendron arboreum) forest which is recognized as the world’s largest forest type located at Annapurna Conservation Area in the temperate region of Nepal. We evaluated the consequences of multiple ecological parameters mainly climatic and biotic factors on SR variations during the month of October in 2016 and 2017. Our results confirmed that SR well corresponded with soil temperature (ST) variables represented with the highly significant ( p < 0.05 ) exponential curve (y = 1.049e0.529x, 2016 and y = 26.34e0.284x, 2017). And the variation in SR was mediated by a short-range (2-3°C) of ST difference in the month of October during autumn season. However, the effect of soil water content (SWC) on SR was scattered and the photosynthetic photon flux density (PPFD) stood weak to represent the SR variation. The seasonal trend of SR was compatible with the PPFD and litter input with having accountable temporal, diurnal, and interannual variations of SR, ST, SWC, and litterfall. The SR over the entire measurement period were averaged at 269.9 mg CO2 m−2·h−1 in 2016 and 295.1 mg CO2 m−2·h−1 in 2017. Our study manifested that temperate forests could store maximum soil carbon with limited emission through SR and become a larger sink of atmospheric carbon dioxide even though SR is very sensitive to environmental changes and interactively affected by multiple ecological factors. Thus, our finding is an appreciable measure for the temperate forest to understand the regional carbon balance and suggested temperate forests are valued to incorporate them in evaluating global carbon budget.

Background: Photosynthetic carbon released into the atmosphere in the form of carbon dioxide (CO2) which represented by soil respiration (SR), is considered the largest carbon (C) efflux of terrestrial ecosystem. Understanding the dynamics of SR is critical to coping with prevailing climate change from regional to global scale. Temperate forests are considered as most fragile hence need to recognize their vulnerability owing to continuous climatic changes and anthropogenic activities. Predicting the response of SR is essential, owing to the varying environmental factors that are most dominantly effective to become common determinants of forest carbon variability. This study aimed to assess SR by using closed chamber method in the natural Rhododendron arboretum forest in Annapurna Conservation Area (ACA) which is recognized as the world’s largest forest type located in a temperate region of Nepal. This research additionally aimed to evaluate the consequences of multiple ecological parameters mainly climatic and biotic factors on SR variations in consecutive two years measurement period in October 2016 and 2017.Results: Overall, SR in the forest well corresponded with the soil temperature (ST) variables. Within a short-range (2-3°C) of ST difference the variation in SR was recognized as highly significant (p<0.05) exponential curve (y=1.049e0.529x, 2016 and y = 26.34e0.284x, 2017). However, the effect of soil water content (SWC) on SR was scattered and clear effects of photosynthetic photon flux density (PPFD) were also not detected. Contrary to ST and SWC, seasonal trend of SR was compatible with the PPFD and litter input. The temporal, diurnal, and inter-annual variations of SR, ST, SWC and litter fall were accountable.Conclusions: Temperate forest could store the maximum amount of soil C with limited C emission through SR and become a larger sink of atmospheric CO2. SR is very sensitive to environmental changes and interactively affected by multiple ecological factors, even though it is often difficult to separate their interactions. This founding research is adequate measure in temperate Rhododendron forest; further study seeks understanding on how C emission responds to the regional climate warming, through changing precipitation and landuse, and integrates these feedbacks into global climate models and carbon budget.