Soil Respiration Dynamics and Environmental Controls Across Montane Forests of Nepal.

Soil respiration (R S) represents a major process of release of carbon dioxide (CO2) from soil to atmospheric carbon pools. Measurements of soil respiration help to understand the dynamics of carbon in ecosystems. This study examines the soil respiration rate and the effect of environmental variables in different forests along elevation gradient. This study was conducted in three distinct montane forest types distributed along an elevational gradient in the middle mountain region of Nepal, namely Schima-Castanopsis Forest, Oak Laurel Forest, and Evergreen Oak Forest. In each forest type, 10 circular chambers were installed for measuring soil respiration. Soil CO2 efflux was measured monthly for 1 year, using the "closed chamber method" with an infrared gas analyzer. Soil respiration rate was modeled as a function of soil temperature and moisture using a generalized linear model (GLM). Soil respiration rate varied significantly among the forest types, ranging from 274.7 to 352.4 mg CO2 m-2 h-1 and demonstrated seasonal changes with a summer peak. Soil respiration was significantly higher in Evergreen Oak Forest than Oak Laurel Forest and Schima-Castanopsis Forest. Response of soil respiration to soil temperature and soil water content indicated a significant exponential relationship in all the forests. Soil respiration showed a strong correlation with soil temperature than soil water content. Temperature sensitivity (Q10) of soil respiration was higher in the forest of upper elevation (Evergreen Oak Forest, Q10 = 3.9) than in the lower elevation forests (Oak Laurel Forest, Q10 = 2.7; Schima Castanopsis Forest, Q10 = 2.5), indicating that soil respiration in the Evergreen Oak Forest is more responsive to temperature changes. Hence, forests at higher elevation are highly susceptible in the context of future climate warming due to enhanced efflux of soil CO2. This study highlights the necessity of incorporating belowground carbon processes into climate policy and sustainable forest management frameworks in Nepal.