不同利用方式下土壤有机碳转化及微生物群落功能多样性变化

 【目的】研究亚热带地区不同土地利用方式下土壤生物和生物化学性状的变化特点，为制订合理的耕作施肥管理措施提供科学参考。【方法】选择亚热带地区的一个小流域，通过田间采样分析，比较了不同土地利用方式下土壤有机碳和养分含量、土壤有机碳矿化以及土壤微生物生物量和微生物群落功能多样性变化。【结果】土壤有机碳、全N含量、土壤微生物生物量碳氮以及土壤的呼吸强度变化均表现为稻田（菜地）＞竹林＞园（旱）地，0～15 cm、15～30 cm稻田（菜地）土壤有机碳和全N含量平均比园（旱）地土壤高76.4%、59.8%和80.8%、67.3%，0～15 cm稻田土壤的微生物生物量碳、氮和土壤呼吸强度分别是园（旱）地土壤的6.36倍、3.63倍、3.20倍。土壤微生物代谢熵园（旱）地＞林地＞稻田，稻田土壤的代谢熵仅为园（旱）地土壤的47.7%。培养期间土壤有机碳矿化量和矿化率稻田＞竹林＞园（旱）地。土壤细菌数量稻田≥园（旱）地＞林地，但真菌和放线菌数量在不同利用方式之间并没有显著差异。土壤微生物的平均吸光值和群落功能多样性指数稻田＞园（旱）地＞林地。研究还揭示，稻田改种蔬菜5 a后，由于大量施用磷肥，土壤速效磷含量显著升高，但土壤有机碳和全氮含量没有明显差异；土壤微生物生物量碳、氮和土壤呼吸强度显著下降了53%、41.5%和41.3%，代谢熵升高了23.6%，土壤有机碳的矿化速率也有下降的趋势；土壤细菌和放线菌数量略有升高但差异不显著，真菌数量显著增加，而土壤微生物群落功能多样性指数却显著下降了。【结论】不同土地利用方式下土壤的生物和生物化学性状有显著不同。稻田利用方式下土壤的有机碳和养分含量、以及土壤有机碳转化过程指标和微生物群落功能多样性等均较该区的旱地和林地土壤高。但若在高肥力稻田上继续过量施用化肥，将有可能造成土壤生物性状和生化功能衰减，导致土壤生物质量退化。

Changes in Transformation of Soil Organic Carbon and Functional Diversity of Soil Microbial Community Under Different Land Use Patterns

【Objective】Changes in soil biological and biochemical properties under different landuse patterns in subtropical region of China were investigated for providing scientific instruction to develop rational measures for cultivation and fertilization management. 【Method】Landuse patterns were selected in a small watershed of subtropical region of China for taking and analysing soil samples to compare the changes in soil organic carbon and nutrient contents, mineralization of soil organic carbon, and soil microbial biomass and community functional diversity. 【Result】Soil organic carbon and total nitrogen contents, microbial biomass C and N, and respiration intensity under different landuse patterns were changed in following order of paddy fields (and vegetable farming) > bamboo stands > fruit trees (and upland), in which paddy field (and vegetable farming) were 76.4%, 80.8% (0~15cm) and 59.8%, 67.3% (15~30cm) higher soil organic carbon and total nitrogen contents than and 6.36, 3.63, 3.20 times soil microbial biomass C, N, respiration intensity of that in fruit trees (and upland), respectively. Soil microbial metabolic quotient was fruit trees (and upland) > forestry land > paddy field, in which metabolic quotient in paddy soil was only 47.7% of that in fruit trees (and upland) soil. Amount and rate of soil organic carbon mineralization during incubation were paddy field > bamboo stands > fruit trees (and upland). Soil bacteria population was paddy field > fruit trees (and upland) > forestry land, while no significant difference existed in fungi and actinomycetes populations. BIOLOG analysis indicated a changing order of paddy field > fruit trees (and upland) > forestry land in value of average well cell development (AWCD) and Shannon, Simpson, McIntosh diversity indexes representing carbon utilization of microorganism. Results also showed that paddy field conversion to vegetable farming for 5 years, which was accompanied by large amount of phosphate fertilizer application, dramatic increase of soil available phosphorus content while insignificant changes in soil organic carbon and total nitrogen content, would caused a decrease of 53%, 41.5%, 41.3% in soil microbial biomass C, N, respiration intensity respectively, an increase of 23.6% in metabolic quotient, and a decrease in soil organic carbon mineralization rate. Soil bacteria and actinomycetes populations were increased slightly, fungi population increased dramatically, and functional diversity indexes of soil microbial community decreased significantly. 【Conclusion】It was suggested that soil biological and biochemical properties were quite different under landuse patterns. Soil organic carbon and nutrient contents, mineralization of organic carbon and functional diversity of microbial community in paddy field were higher than that in upland and forestry land in subtropical region of China. While, overuse of chemical fertilizers for a paddy field with high fertility would cause decrease of soil biological properties and biochemical function, resulted in deterioration of soil biological quality.