亚热带地区阔叶林与杉木林土壤活性有机质比较

通过对亚热带3个地区地带性阔叶林和杉木林土壤活性有机质的比较，分析森林类型变化及杉木连栽对土壤有机碳和养分含量的影响.结果表明：地带性阔叶林转变为杉木林后，土壤总有机碳含量下降27.8%～52.1%、腐殖酸碳下降32.2%～52.8%、胡敏酸下降36.4%～59.0%、富里酸下降29.7%～50.0%；杉木连栽也使土壤总有机碳和腐殖质含量下降.森林类型改变和杉木连栽对土壤活性有机质的影响更明显.杉木林取代阔叶林后，土壤微生物生物量碳、微生物生物量氮、可溶性有机碳和可溶性有机氮含量的最大降幅分别为61.8%、38.2%、43.3%和69.0%；与第1代杉木林相比，第2代杉木林土壤微生物生物量碳、微生物生物量氮、可溶性有机碳和可溶性有机氮含量的最大降幅分别为34.7%、29.3%、30.4%、18.4%.经相关性分析，除冷水浸提有机氮外，土壤活性有机质与养分含量之间具有密切的相关关系.

Soil active organic matter in broadleaved forest and Chinese fir plantation in subtropical region of China

A comparative study was made on the soil active organic matter in a broadleaved forest and two Chinese fir (Cunninghamia lanceolata) plantations in subtropical region of China, aimed to understand the effects of forest conversion and continuous plantation on soil organic C and nutrient status. After the conversion from broadleaved forest to Chinese fir plantation, the contents of soil total organic C, humus C, humic acid, and fulvic acid decreased by 27.8%-52.1%, 32.2%-52.8%, 36.4%-59.0%, and 29.7%-50.0%, respectively. Continuous plantation also resulted in the decrease of soil organic C and humus contents. The contents of soil total organic C, humus C, humic acid, and fulvic acid in second generation of Chinese fir plantation were 9.0%-25.0%, 25.0%-38.0%, 28.6%-39.2% and 23.1%-36.4% lower than those in the first generation of Chinese fir plantation, respectively. More obvious effects were observed on the soil active organic matter. After the conversion from broadleaved forest to Chinese fir plantation, the maximum decrement of soil microbial biomass C and N and dissolved organic C and N was 61.8%, 38.2%, 43.3%, and 69.0%; while comparing with the first generation of Chinese fir plantation, the second generation of Chinese fir plantation had the maximum decrement of soil microbial biomass C and N and dissolved organic C and N being 34.7%, 29.3%, 30.4%, and 18.4%, respectively. Soil nutrient contents also decreased due to forest conversion and continuous plantation. In comparing with broadleaved forests, Chinese fir plantations had a decrease of soil N, P, and K contents being 15.7%-31.2%, 11.5%-49.3%, and 15.1%-33.8%, respectively. There were close relationships between soil nutrients and soil active organic matter fractions except cold water extractable organic N.