Abstract
Carbon cycle studies over the climate-sensitive Himalayan regions are relatively understudied and to address this gap, systematic measurements on carbon balance components were performed over a deciduous pine forest with an understory layer. We determined annual net carbon balance, seasonality in components of carbon balance, and their environmental controls. Results indicated a strong seasonality in the behavior of carbon exchange components. Net primary productivity (NPP) of pine forest exceeded soil respiration during the growing phase. Consequently, net ecosystem exchange exhibited a net carbon uptake. In the initial phase of the growing season, daily mean uptake was −3.93 (±0.50) g C m−2 day−1, which maximizes (−8.47 ± 2.3) later during post-monsoon. However, a brief phase of carbon release was observed during peak monsoon (August) owing to an overcast condition. Nevertheless, annually the forest remained as a carbon sink. The understory is extensively distributed and it turned out to be a key component of carbon balance because of sustained NPP during the pine leafless period. Temperature and evaporative fraction exhibited a prime control over the seasonal carbon dynamics. Our observations could lend certain useful insights into the application of coupled climate-carbon cycle models for the Himalaya and ecological functions in the region.
Highlights
During the last two centuries, anthropogenic CO2 emissions and deforestation have increased the surface temperature significantly
Our results showed that Carbon use efficiency (CUE) varied from 0.3 to 0.87 across the seasons and the mean growing season CUE was 0.74 ± 0.02
Subtropical deciduous pine forests in western Himalaya regions are underrepresented in global assessments concerning forest carbon dynamics and productivity, and so far no comprehensive in situ data were available on carbon exchange dynamics from pine forests
Summary
During the last two centuries, anthropogenic CO2 emissions and deforestation have increased the surface temperature significantly. The built-up CO2 in the atmosphere causes global warming, whose future extent will depend on the size of future emissions, and on the development of future carbon (C) sinks of the terrestrial biosphere and ocean. Terrestrial biosphere, together with the ocean help by drawing down more than 50% of the annual anthropogenic CO2 emissions, and their. The future trend of C sink largely depends on the responses of terrestrial ecosystems to increasing CO2 concentrations and climate change [2]. The C balance of terrestrial ecosystems can be represented by both the net ecosystem productivity (NEP) and net ecosystem carbon exchange (NEE). The balance between ecosystem respiration (Re) and gross primary productivity (GPP) determines NEE, which can be positive (i.e., carbon source) or Resources 2019, 8, 98; doi:10.3390/resources8020098 www.mdpi.com/journal/resources
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