Effect Of Land-use Types On Microbial Properties And Nitrogen Transformation In Red Soils Of Southeastern China

Tropical and subtropical red soil in southeast China cover about1.13million km2or11.8%of the country’s land surface, and support22.5%of the nation’s population. Red soil is characterized with low pH, poor nutrition, higher nitrogen, low nitrification, low denitrification and abundant N2O emission. The distribution of red soil has obvious regional characteristic. The land use change, such as the conversion of the natural forests to agricultural purpose, might affect soil fertility and soil function. Therefore, it will be instructive to progress of the effect of land-use types on microbial properties and nitrogen transformation for sustainable development of red soil in China.The representative land-use types of tropical and subtropical red soils in southeastern China were investigated in this paper:the first series including a natural secondary forest (NSF), a banana plantation (BAN), a eucalyptus forest (EUC), and a rubber plantation (RUB) in Qiongzhong, Hainan province; the sencond series including four natural forests, Altingia gralilipes (ALG), Cinnamomum chekiangense (CIC), Castanopsis fargesii (CAF), Tsoongiodendron odorum (TSO), and two plantations, Cunninghamia lanceolata (CUL) and Citrus reticulata orchard (ORG) in Jian’ou, Fujian province; the third series including three soil parent materials:granite (G), tertiary red sandstone (R), and quaternary red earth (Q) and four land use patterns:broad-leaf forest (B), conifer forest (C), shrub land (S) and upland/farmland (U/F) in Yingtan, Jiangxi province. In this study, soil nitrification potential (NP) and recovery of nitrification potential (RNP) were measured; soil denitrification and its gas products (N2O, NO, N2) were studied by acetylene inhibition method applied to laboratory incubation under flooded condition; real-time quantitative polymerase chain reaction (qPCR) was conducted to investigate amoA gene copies of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), narG, nirK, norB, nosZ gene copies of denitrifying bacteria and soil16S rRNA bacterial gene copies; denaturing gradient gel electrophoresis (DGGE) was conducted to investigate soil16S rRNA bacterial diversity; phospholipid fatty acid analysis (PLFA) was conducted to investigate soil microbial diversity.Soil microbial biomass and soil enzyme activities were significantly differed in different land-use soils. The agricultural land-use had lower soil microbial biomass carbon and nitrogen and soil urease and dehydrogenase activities than other land-use soils. These significantle difference might be driven by changes of soil nutrition factors (soil organic carbon, total N. available N, available K et al.) according to correlation analysis. Land use types had great effects on soil microbial community structure in the mid-subtropic region of China. Soil microbial diversity were highest under four natural forests (CIC, CAF, ALG, TSO), followed by CUL platation, whilst least in orchard soil. The conversion from native forests to agricultural purpose could decrease soil microbial biomass, activity and diversity in mid-subtropical region of China. Litterfall, soil oganic C and soil total N distinguished the microbial community of forests from that of economic plantation in the mid-subtropical China.Our result showed that soil nitrification potential (NP) of natural forest was significantly lower in Jiangxi than Fujian and Hainan; NP of framland use soils was higher than natural forest soils in all soil series. It indicated that deliberate management might increase soil denitrification activity. Contribution rate to nitrification of AOB and AOA was differed from different land-use types. Relative analysis between NP and amoA gene copies of AOB and AOA from qPCR analysis indicated that soil nitrification potential could be mediated by AOB in Fujian and Hainan soil samples:nitrification potential might be mediated by AOA in Jiangxi. Further study of sensitivity of RNPs to protein synthesis inhibitors suggested that soil NP of BAN, EUC, RUB in Hainan and CIC, CUL,ORG in Fujian could be attributed exclusively to AOB; in contrast, those nitrification potential NSF in Hainan, ALG in Fujian, RB, RC, RS, RU in Jiangxi were mediated by AOA.Soil denitrification potential and composition of denitrification products varied greatly among the investigated soils with a following order of denitrification potential:GF (0.120 mg·kg-1·h-1)> GS (0.056mg·kg-1·h-1)> GC (0.052mg·kg-1·h-1)> QF (0.018mg·kg-1·h-1)> QC (0.010mg·kg-1·h-1)> QS (0.009mg·kg-1·h-1). NO/(N2O+NO+N2) was higher in quaternary red earth than granite soil. The dominant denitrification gas product was N2O in conifer forest (C) and shrub land (S) soils and N2in farmland (F) soil. Soil denitrification potential was higher in farmland soil than in conifer forest and shrub land soils.Soil pH was the important influence factor of the denitrification. Among the four genes:narG, nirK, norB and nosZ, the norB gene was the key factor of the difference of denitrification in different land-use soils.