红壤区桉树人工林炼山后土壤肥力变化及其生态评价

Abstract

Controlled burning is a traditional forest-clearing method used in Southern China. We analyzed the variability of soil fertility between controlled burning and non-burnt areas in a Eucalyptus robusta plantation forest of the red soil region, located in Hengxian County in Guangxi Zhuang Autonomous Region,China. Traditional incubation and culture-independent methods,such as the dilution-plate method,the polymerase chain reaction,and denaturing gradient gel electrophoresis( PCR-DGGE) were used. Possible effects on the soil ecological system were also evaluated. Soil organic matter( SOM), total and available nitrogen,phosphorus and potassium contents in the 0—3 cm soil layer only one week after burning were all higher than those in a non-burnt Eucalyptus forest. The number of soil culturable microbes,which includes bacteria, fungi and actinomycetes,and the biomass C and N in the 0—3 cm layer were also significantly higher than those in the nonburnt Eucalyptus forest. Indexes of chemical and biological properties in the middle layer( 3—25cm) of the burnt soils also showed the same trends observed in the surface soil layer. However,irregular changes were found in these chemical and biological indexes in soil layers below 25cm. This indicates that the chemical and biological properties of soils,including soil organic matter( SOM),total and available nitrogen,phosphorus and potassium,as well as the number of soil culturable microbes,and the biomass C and N in layer below 25cm were not significantly impacted by controlled burning. Furthermore,four months after controlled burning,except for total and available phosphorus contents,nutrients such as total and available nitrogen,potassium and SOM contents did not show the same trends with burning as were found after one week,and were all lower than those in the non-burnt forest soil. Also,the number of soil culturable microbes,and the biomass C and N in each layer of the burnt soils were also lower than those in the non-burnt soil. Thus,controlled burning in the Eucalyptus plantations in the red soil region of southern China has only short-term beneficial effects on soil fertility, and is not helpful for improving long-term soil fertility of Eucalyptus plantations. Indexes of soil bacterial diversity( Shannon-Wiener,H),Richness and Evenness( E H) in each layer after burning showed irregular changes. However,in the surface soil layers( 0—3cm) of the burnt treatments these indexes were all lower than those in the non-burnt treatment and hardly recovered to the same level as in the non-burnt treatment 4 months after burning. These results suggest that the method of controlled burning in southern China might not only result in a decline in soil fertility with time,but also lead to a decrease in the indexes of soil bacterial diversity,Richness and Evenness,in surface soils in these two periods after burning. Thus,based on the above results,controlled burning is not helpful for improving the soil fertility and maintaining the development of a sustainable surface soil ecosystem in Eucalyptus plantations in the red soil region of southern China.