Wet and dry spell induced changes in the soil CO₂ effluxes of Pine and Oak ecosystems of Central Himalaya: a comparative assessment for monsoon and winter seasons

Soil efflux of CO₂ ( $F_{{\mathrm{CO}}_2}$ ) is known to be dependent on natural drying and rewetting of the soil. Although the central Indian Himalayan region is predominantly occupied with two ecosystems, i. e. Pine (Pinus roxburghii) and Oak (Quercus leucotrichophora), differences in their $F_{{\mathrm{CO}}_2}$ dynamics and responses of $F_{{\mathrm{CO}}_2}$ to varying wet and dry spells were hardly known. To address this knowledge gap, this study provides a comparative assessment of $F_{{\mathrm{CO}}_2}$ variability from Pine and Oak ecosystems of central Himalaya as a response to rainfall induced wet and dry spells of monsoon and winter seasons. The $F_{{\mathrm{CO}}_2}$ data presented in this study are collected for 242 days of 2021-22 that include monsoon and winter seasons from a Pine and an Oak sites. The mean $F_{{\mathrm{CO}}_2}$ _s of Pine and Oak sites are found to be 3.95(± 0.02) and 3.61(± 0.01) μmol.m^-2.s^-1, respectively. We find that the winter reduction in the $F_{{\mathrm{CO}}_2}$ in comparison to monsoon at the Pine site (78%) is more substantial than at Oak site (64.6%). The cross wavelet spectra of $F_{{\mathrm{CO}}_2}$ and monsoon rainfall amount at the Oak site, unlike the Pine site, indicate a negative relationship. The rainfall spell duration and amount of monsoon wet spells are noted to have an inverse relationship with $F_{{\mathrm{CO}}_2}$ at both sites, although, increasing rainfall spell duration in winter is noted to increase $F_{{\mathrm{CO}}_2}$ at Pine and Oak sites. Similarly, increasing $F_{{\mathrm{CO}}_2}$ is observed with increasing dry spells of monsoon at both sites. Results of this study indicate that in comparison to Oak, $F_{{\mathrm{CO}}_2}$ variability at Pine ecosystem is primarily driven by abiotic factors wherein wet spell is a major determinant.