Temporal variability in fine root dynamics in relation to tree girth size in sub-tropical sal (Shorea robusta) forests

In forest ecosystems, the rapid turnover of fine roots (<= 2 mm in diameter) is a major pathway of carbon and nutrient flow from plants to the soil. This study was conducted to determine how fine root biomass (FRB), productivity (FRP) and turnover (FRT) are affected by site characteristics, seasonal variation, soil depth and tree girth size in sub-tropical sal forest ecosystem. Four sites (S1, S2, S3 and S4) were established in the Bhabhar region of Nainital istrict, Uttarakhand, India within an elevational range of 405 and 580 m, and at each site, sal trees were categorized into five girth classes. Fine roots were sampled seasonally up to a depth of 60 cm and divided into three layers (0-20, 20-40 and 40-60 cm). FRB was significantly affected by tree girth size and decreased with increasing girth size, while the effect of tree girth on FRP and FRT was observed to be insignificant. Seasonal variation of FRB in all girth sizes showed a keen resemblance as the standing FRB reached its pinnacle during the rainy season and the bottom line in the winter season. Maximum FRB was reported for the uppermost, organo-mineral-rich soil depth (0-20 cm) at 1.0 m distance from the tree bole and decreased with increasing soil depth and distance from the tree bole while FRT showed a reverse trend. The present study provided a holistic outlook on variations in FRB, FRP and FRT and the impact of edaphic characteristics and tree girth on fine root dynamics in the sal forest ecosystem of Central Himalaya, India.