# Net Ecosystem Exchange of CO\({}_{2}\) in Deciduous Pine Forest of Lower Western Himalaya, India
## 3 Results
### Seasonal Variations in NPP, Rs, and NEE  
The behavior of carbon fluxes (NPP, \(R\)s, and NEE) across the seasons such as winter 2010 (no understory), pre- and post-monsoon (comprising the growing period: April-October), and winter 2011 (with understory) has been shown in Figure 1. With the advent of the growth conducive spring season, the increment in NPP was remarkable. It attained peak in the post-monsoon season (23.6 \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)). Results also indicated a dropdown in NPP from July3d (10 day intervals: \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variables** & **Characteristics** & **Remarks** \\ \hline Annual Rainfall & 2020 \(\pm\) 423 mm & Average over 1940–2010, \\  & & Peak during July–August \\ \hline Air Temperature & 11.5 \({}^{\circ}\)C (January), 27 \({}^{\circ}\)C (June) & Peak during May–June \\ \hline Humidity & 52\% (April), 85\% (August) & Lowest (summer season), \\  & & Maximum (rainy season) \\ \hline Sunshine & 4.4 h day\({}^{-1}\) to 9.3 h day\({}^{-1}\) & Minimum (July–August), \\  & & Maximum (May) \\ \hline Pan Evaporation & 1.2 mm to 7.2 mm & Minimum (December), \\  & & Maximum (May) \\ \hline Vapor Pressure Deficit (VPD) & 0.37 kPa to 3.7 kPa & Lowest (monsoon), \\  & & Highest (summer) \\ \hline Soil Moisture & 10\% to 24\% (mean of the three-soil & Lowest in May (summer), \\  & layer: 0.05 m, 0.2 m, and 0.45 m) & Maximum (rainy season) \\ \hline Soil type & Mollisols & 3–8 m thickness, \\  & & Porosity 40–60\% \\ \hline Soil Texture & Sandy clay loam & 35\% sand, 40\% clay, and 25\% silt \\ \hline Soil pH & 4.5–6 & Acidic \\ \hline Bulk density & 1030 kg m\({}^{-3}\) & 0–20 cm depth \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean climatic (subtropical) and soil characteristics of the study site. 21-30 July) to Aug3d (21-30 August) that has been attributed to decline in photosynthesis owing to an overcast condition during the rainy season (i.e., limited incoming solar radiation input including PAR). The mean NPP over the growing period (April-October) was observed at \(11.75\pm 1.25\) (s.e.) \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) (CV: 49%). NPP was minimum (\(0.7\pm 0.14\)) during winter 2010 (no understory and dormant overstory), while it was almost \(11\) times higher during winter 2011 (\(7.9\pm 1.96\)\(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)) due to the presence of an understory. The annual cycle of soil respiration (\(R\)s) was bimodal (Figure 1). With leaf onset during spring (March-April), a smaller peak (7-8 \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)) was noticed. \(R\)s attained peak in the post-monsoon season (12-15 \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\); Figure 1). Mean \(R\)s over the growing period was \(9.2\pm 2.8\) (s.e.) \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) (CV: 30%). \(R\)s rates declined with the advancement of summer owing to water limitation (or declined soil moisture). Thereafter, it increased with the arrival of monsoon and again declined during winter. During winter 2010 and 2011, \(R\)s rates were \(6.3\pm 0.17\) and \(7.25\pm 0.24\)\(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\), respectively. The coefficient of variation (CV) in these periods were \(10.7\%\) and \(8.2\%\), respectively, reflecting a feeble role of photosynthates from the understory and overstory on \(R\)s during the winter physiological state. NEE varied to a large extent during the observational period that ranged from \(-12.8\)\(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) to \(6.3\)\(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\), with an average of \(-3.3\pm 1.65\) (s.e.) \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) over the peak growing period (June-October). NEE was negative (carbon sink) mostly over the growing period (Figure 1). However, within the growing period, NEE attained a positive level (carbon source) in the peak monsoon season (July3d-Aug3d), owing to response of carbon processes to ambient environmental conditions.