The effect of Indian summer monsoon on the seasonal variation of carbon sequestration by a forest ecosystem over North-East India

The Indian summer monsoon is one of the most important yet less understood synoptic processes on the Earth, characterized by an increased amount of rainfall over the entire Indian landmass. The different types of forest ecosystems existing over the Indian region offer a tremendous carbon sequestration potential useful for the global mitigation of climate change as predicted by the modelling studies. The monsoon results in a strong seasonality of the ecosystem-atmosphere carbon exchange due to the differential availability of two key controlling parameters of photosynthesis namely radiation and water. However, due to the sparsity of surface observations neither the carbon sequestration potential of these ecosystems nor its relation with the monsoon has been analysed comprehensively so far. This paper studies the ecosystem-atmosphere CO₂ exchange at a tropical semi-evergreen moist deciduous forest and its relation with the monsoon over north-east India using the eddy covariance and associated meteorological measurements. In 2016, this ecosystem acts as a net source of atmospheric CO₂ with net ecosystem exchange of 207.51 ± 157.37 gC m⁻² year⁻¹ and gross photosynthesis and ecosystem respiration of 2604.88 ± 179.43 and 2812.38 ± 22.05 gC m⁻² year⁻¹, respectively. The monsoon clouds are seen to introduce a bimodal pattern in the annual GPP record. The pre-monsoon and winter are the most and least favourable seasons for the photosynthetic CO₂ uptake by this forest canopy. Additionally, the rate of increase of photosynthesis with evapotranspiration is maximum and minimum during the pre-monsoon and winter, respectively.