Soil organic matter under different forest types in southern China

Conversion of native broadleaved forests to pure coniferous plantation is a common management practice driven by an increasing demand for timber production. A study was conducted to evaluate the impact of land-use change from native broadleaved forest to pure coniferous plantation on soil organic matter quantity and quality in San Menjiang Forest, in southern China. Additionally, the potential of hot-water extractable organic matter as an indicator of changes in SOM was also assessed. Significant differences in labile SOM fractions (hot-water extractable organic C and total N, cold-water extractable organic C and total N, and microbial biomass C and N) between pure Cunninghamia lanceolata Hook plantation and native broadleaved forest were tested using ANOVA. The contents of soil organic C, total N, and labile organic matter such as hot-water extractable organic C and total N, cold-water extractable organic C and total N, and microbial biomass was significantly lower in pure C. lanceolata plantation than in native broadleaved forest. The percentage ratios of hot-water extractable organic C and N, cold-water extractable organic C, and microbial biomass C and N to soil organic C or total N were also significantly reduced in C. lanceolata plantation. Hot-water extractable organic C and total N were significantly correlated with cold-water extractable organic C and total N and microbial biomass C and N in both native broadleaved forest and pure coniferous plantation (r > 0.608, P < 0.01). The correlation coefficients between hot-water extractable organic matter and soil organic C or total N (r > 0.694, P < 0.01) were higher than that between cold-water extractable organic matter, microbial biomass and soil organic C or total N (r > 0.525, P < 0.05). Therefore, land-use change from native broadleaved forest to coniferous plantation reduced soil organic matter quantity and quality, and hot-water extractable organic matter can be used as an indicator of changes in SOM quality in forest soils. (C) 2007 Published by Elsevier B.V.