Chemistry of decomposing mulching materials and the effect on soil carbon dynamics under a Phyllostachys praecox bamboo stand

Heavy winter mulch treatments are commonly practiced in Phyllostachys praecox bamboo forests to increase bamboo shoot production in early spring in subtropical China. The aim of this study was to quantify the chemical behaviour of the mulching materials and the immediate response of soil carbon (C) to the heavy winter mulch treatments. In the field study, in situ decomposition rates of the mulching materials, including bamboo leaves and rice straw, and soil respiration rates were determined. The chemical behaviour of the mulching materials and the impacts of the mulches on soil C dynamics were evaluated using solid state C-13 NMR spectroscopy. During the 12-month experimental period, bamboo leaves (C/N ratio, 20) lost 79 % of their mass, whereas rice straw (C/N, 49) lost 67 %. Mulch treatment enhanced soil respiration rate. The residual materials had a significantly higher alkyl C to O-alkyl C ratio, but lower aromaticity than those in the original materials. The soil beneath the mulches rapidly built up organic C, which was dominated by O-alkyl C with reduced aromaticity. Application of heavy mulch in a Phyllostachys praecox bamboo plantation can enhance sequestration of soil C; however, the relatively low aromatic C character would indicate that it is likely to be labile.