Organic mulch and fertilization affect soil carbon pools and forms under intensively managed bamboo (Phyllostachys praecox) forests in southeast China

Phyllostachys praecox is one of the bamboo species used for the production of fine edible bamboo shoots and is widely distributed in Southern China. To maintain or increase the productivity of bamboo shoots, P. praecox forests are intensively managed through heavy fertilization and surface mulch of organic residues such as rice husk to increase soil temperature in the winter. Such management techniques can markedly influence soil quality and the dynamics of soil carbon (C). The objectives of this study were to investigate the long-term impact of intensive management practices on carbon pools and forms in the soil of bamboo forests and explore relationships between different soil organic C fractions, as little such information is currently available. In this study we use a chronosequence (consisting of bamboo forests 1, 5, 10, and 15 years under intensive management) approach to investigate the long-term impact of intensive bamboo forest management on water-soluble organic C (WSOC), hot water-soluble organic C (HWSOC), microbial biomass C (MBC), and readily oxidizable C (ROC) as well as soil organic C chemistry using the (13)C-nuclear magnetic resonance (NMR) technique. Total soil organic C, WSOC, HWSOC, and ROC increased with time under intensive management, while MBC initially increased then decreased. Solid state NMR spectroscopy of soil samples showed that alkyl C and O-alkyl C dominated soil organic C in the intensively managed bamboo forests, alkyl C content and alkyl C to O-alkyl C ratio increased, aromatic C content, and aromaticity of organic matter decreased, while O-alkyl C did not change as duration under intensive management increased. The WSOC and total soil O-alkyl C contents were positively correlated, indicating that O-alkyl C may be the main component of WSOC, consistent with solution (13)C-NMR spectroscopy for WSOC in which O-alkyl C dominated the WSOC fraction regardless of the treatment. Organic matter aromaticity was negatively correlated with HWSOC, indicating that aromaticity was a good indicator of soil organic C stability. We conclude that long-term application of organic mulch over winter increased total soil organic C content but decreased its stability. Mulching of organic residues in intensively managed bamboo forests is beneficial in increasing the sequestration of organic C in those forest ecosystems. Future research should address the impact of intensive management practices on water quality since the decreased stability of organic C increases the risk of its movement.