Inconsistent responses of forest floor respiration and its components to disturbance regimes across seasonal phases in Shorea robusta forests in Western Himalaya

Carbon (C) storage capacity of sal (Shorea robusta) forests in the western Himalaya is increasingly threatened by rising disturbance intensity, particularly logging. Disturbances significantly influence forest floor respiration (R_ff) by affecting fine root biomass (FRB), soil properties (temperature, moisture, bulk density (BD)), N availability (nitrate and ammonium ions), and microbial biomass carbon (MBC). However, interactive effects of disturbances and seasonal conditions on R_ff and its components (heterotrophic (R_h) and autotrophic (R_a) respiration) remain poorly understood. This study investigated R_h and R_a across three growing seasons using trenching method in sal forests under four disturbance regimes (no disturbance (ND): < 5 % basal area removal, low disturbance (LD): <20 %, moderate disturbance (MD): <50 %, and high disturbance (HD): >50 %).

R_ff in HD stands were 13.7 %, 9.2 %, and 10.9 % higher than ND, LD, and MD stands, respectively, due to a substantial increase in R_a, which was 39.2 %, 30.6 %, and 51.1 % higher than in ND, LD, and MD stands. Conversely, R_h was 6.3 %, 3.4 %, and 2.9 % greater in MD stands compared to ND, LD, and HD stands, likely due to enhanced soil organic carbon (SOC), moisture, N availability, and MBC. Model predictions indicated that variations in R_h and R_a contributions were primarily driven by microbial quotient (Qmic, MBC: SOC ratio), N availability, and soil properties, particularly BD, moisture, and temperature, influenced by disturbances and seasonal changes. Path analysis reveals, R_ff and its components are regulated by distinct ecological drivers, with N availability and microbial properties playing key roles. Our findings demonstrated that R_h and R_a respond independently to disturbance regimes across seasons and that increased N availability and moisture reduce the temperature sensitivity of R_ff. These findings enhance understanding of how disturbances, through vegetation and soil bio-physicochemical processes, influence C efflux rates, essential for improving predictions of C balance in forest ecosystems.