Soil Respiration Rate and Climatic Parameters from Mixed and Broad-leaved forest sites from Bhutan, Eastern Himalayas for 2015

The biogeochemistry of mountain forests in the Hindu Kush-Himalaya range is poorly studied although climate change is expected to disproportionally affect the region. We measured the soil CO2 efflux (Rs) at a high elevation (3260 m) mixed, and a lower elevation (2460 m) broadleaved forest in Bhutan, eastern Himalayas, during 2015. Trenching was applied to estimate the contribution of autotrophic (Ra) and heterotrophic (Rh) soil respiration. The temperature (Q10) and the moisture sensitivities of Rh were determined under controlled laboratory conditions and were used to model Rh in the field. The higher elevation mixed forest had a higher standing tree stock, reflected in higher soil C stocks and basal soil respiration. Annual Rs was similar between the two forest sites (14.5 ± 1.2 t C yr-1 broadleaved; 12.8 ± 1.0 t C yr-1 mixed). Modelled annual contribution of Rh was ~ 65 % of Rs at both sites with a higher heterotrophic contribution during winter and lower contribution during the monsoon season. Rh, estimated from trenching, was in the range of modelled Rh but showed higher temporal variability. Measured temperature sensitivity of Rh was similar at the mixed and broadleaved forest site (Q10 2.2- 2.3) under intermediate soil moisture but decreased (Q10 1.5 at both sites) in dry soil. Rs closely followed the annual course of field soil temperature at both sites. Co-variation between soil temperature and moisture (cold-dry winters, warm-wet summers) likely was the main cause for this tight relationship. Under the prevailing weather conditions, a simple temperature-driven model was able to explain more than 90 % of the temporal variation in Rs. Longer time series and/or experimental climate manipulations are required to understand the effects of eventually occurring climate extremes such as monsoon failures.