# Net Ecosystem Exchange of CO\({}_{2}\) in Deciduous Pine Forest of Lower Western Himalaya, India
## 1 Introduction  
During the last two centuries, anthropogenic CO\({}_{2}\) emissions and deforestation have increased the surface temperature significantly. The built-up CO\({}_{2}\) in the atmosphere causes global warming, whose future extent will not only depend on the size of future emissions, but also 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 CO\({}_{2}\) emissions, and their C sink strength have continuously improved over the past five decades [1]. However, the future trend of C sink largely depends on the responses of terrestrial ecosystems to increasing CO\({}_{2}\) concentrations and climate change [2]. Further, the terrestrial C sink is mostly controlled by the forest ecosystems and associated environmental drivers [3]. 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) ornegative (i.e., carbon sink). NEP can be represented by the difference between net primary productivity (NPP) and heterotrophic ecosystem respiration. The variability of NEE is tightly coupled with the variations of C balance components, namely, GPP and Re, and their responses to environmental variables and climate [4]. Previous studies have underlined that GPP can be influenced by both environmental (i.e., radiation, rainfall, temperature, vapor pressure deficit (VPD), etc.) and biophysical variables (i.e., leaf area index), whereas, \(R\)e is primarily regulated by environmental variables, such as temperature and soil moisture [5; 6; 7]. Further, the variability of \(R\)e can be largely biased by the constraints in night-time respiration data availability [7; 8]. Thus, it becomes essential to decipher the variability and controls of individual components of carbon balance to understand mechanisms and processes controlling seasonal and inter-annual variability of NEE. In particular, processes and mechanisms controlling NEE and their responses to changing environment across the Himalayan ecosystems are usually unknown. Over the last few decades, Himalayan ecosystems have experienced increased temperatures and abrupt changes in the precipitation pattern [9; 10]. In view of such rapid environmental change, it becomes imperative to study the components of C balance and to evaluate whether the ecosystem is a carbon source or sink. Ecosystem productivity can be derived from varieties of methods, which have their own applicability, strengths and limitations (such as, atmospheric CO\({}_{2}\) inversion (estimate surface-to-atmosphere net C flux), field inventory and book-keeping models, biogeochemical process-based models, satellite data, and flux tower). This study has utilized a combination of chamber-based and micrometeorological methods for understanding and quantifying NEE to determine the sink-source status along with controlling environmental factors. The deciduous pine forest, _Pinus roxburgtii_, is a dominant vegetation type in the lower western Himalayan region (elevation: 500-2000 m) and it encompasses 18,650 km\({}^{2}\) area that represents about 6% of the total forested land of India [11]. Given its climatic (subtropical) and ecological importance, we had investigated the radiation-energy balance and inter-linkages of canopy photosynthesis (\(Ac\)), and water fluxes across the seasons [12; 13]. The results underlined that the degree of coupling between water and C exchange was stronger during transition phases (post-monsoon and spring seasons) [12; 13]. Further, we have investigated seasonal dynamics of canopy and soil respiration fluxes based on in situ field measurements. We observed the temporal dynamics of night-time canopy respiration (\(R\)nc) and soil respiration (\(R\)s) fluxes.