Effects of litter types, microsite and root diameters on litter decomposition in Pinus sylvestris plantations of northern China

Litter decomposition is a major process in the carbon (C) flow and nutrient cycling of terrestrial ecosystems, but the effects of litter type, microsite, and root diameter on decomposition are poorly understood. Litterbags were used to examine the decomposition rate of leaf litter and roots at three soil depths (5, 10 and 20 cm) over a 470-day period in Pinus sylvestris plantations in northern China. Leaves and the finest roots decomposed more quickly at 5 cm depth and coarser roots (> 1-mm) decomposed more quickly at 10 and 20 cm depth. Roots generally decomposed more quickly than leaf litter, except at 5 cm deep; leaves decomposed more quickly than the coarsest roots (> 5-mm). Root decomposition was strongly influenced by root diameter. Leaves experienced net nitrogen (N) immobilization and coarse roots (> 2-mm) experienced more N release than fine roots. Significant heterogeneity was seen in N release for fine-roots (< 2-mm) with N immobilization occurring in smaller (0.5-2-mm) roots and N release in the finest roots (< 0.5-mm). Soil depth of litter placement significantly influenced the relative contribution of the decomposition of leaves and roots of different diameters to carbon and nutrient cycling.