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.