Characteristics And Evolution Of Ammonia-oxidizing And Nitrogen-fixing Bacteria In Moso Bamboo(phyllostachys Pubescens)forest Soils

Moso bamboo is one of the excellent bamboo species with a set of economic, ecological and social benefits. Many broadleaf forests and Chinese fir forests were converted to Moso bamboo,and Moso bamboo naturally invade adjacent forest and formed a new pure Moso bamboo forest,and the area of Moso bamboo forest had reached 4.43 million hectares up to 2013. Soil nitrogen is essential to the growth of Moso bamboo and nitrogen transformation is mainly droved by soil microbial organisms. The objective of this study was to disclose the characteristics and evolution of soil ammonia oxidation microorganisms and nitrogen-fixing bacteria by the methods of denaturing gradient gel electrophoresis(DGGE) and real-time quantitative PCR(Real-time PCR),and the relationship with the process of nitrogen transformation and the availability of nitrogen(N)by combination with determination of soil physical and chemical properties, and soil net rate of nitrogen mineralization and nitrogen nitrification. Topsoil(0-20 cm) and subsoil(20-40 cm) were collected respectively from Moso bamboo and broadleaf forest in county Lin’an and An’ji, and topsoil(0-20 cm) were collected respectively 3 Moso bamboo invasion series including 3 forest types of Moso bamboo, broadleaf and mixed forest in Meishan Changxing County and Qinglongshan and Shimendong in National Nature Reserve of Mount Tianmu. The main results obtained were as follows:1.Comparison of Moso bamboo and broadleaf forest: In Lin’an, soil pH, available N in both soil layers and potassium(K) in topsoil were greater(P<0.05) in bamboo than those in broadleaf forest, and the opposite was true for soil phosphorus(P). The relative less difference in soil physical and chemical properties were observed in An’ji between bamboo and broadleaf forest,only topsoil P and subsoil organic carbon(OC) are observed significant higher(P<0.05) in bamboo forest. Soil net rates of nitrogen mineralization and nitrification were significantly higher(P<0.05) in Moso bamboo forest than broadleaf forest when comparison between the same soil layer, except for net nitrification rate of subsoil. Abundance of ammonia-oxidizing archaea(AOA)functional gene(amoA) was higher in Moso bamboo than broadleaf forest in both Lin’an and An’ji,but significant differences(P<0.05) only observed in An’ji. Abundance of ammonia-oxidizing bacteria(AOB) functional gene(amo A) was generally higher in Moso bamboo forest, but significant difference(P<0.05) was only observed for the topsoil in Lin’an forest. Moso bambooforest soil exhibited lower diversity(Shannon index H) of nitrogen-fixing bacteria evidence from PCR-DGGE, but higher nifH gene abundance compared to broadleaf forest evidence form Real-time PCR. Cluster analysis and principal component analysis(PCA) based on PCR-DGGE profile showed that nitrogen-fixing bacteria community structure was quite different between two forest types.2. Moso bamboo invasion of native broadleaf forest: With bamboo invasion of broadleaf forest, soil pH increased gradually in all three invasion series, so did soil OC and available N in Shimendong, soil OC and available P in Shimendong, while soil OC and available K in Meishan,and available K in Shimendong decreased. Soil net rates of nitrogen mineralization and nitrification were significantly higher(P<0.05) in Moso bamboo forest than those in broadleaf forest when comparison between forests in the same invasion series, except for net nitrification rate in Shimendong. The gene amoA abundance of AOA and AOB decreased with bamboo invasion of broadleaf forest. Diversity Shannon index H(based on DGGE bands information) of nitrogen-fixing bacterial in broadleaf forest was significantly greater(P<0.05) than those in other two forests in Meishan, while the opposite was true for diversity index in Qinglongshan, there is no significant difference between three types of forest in Shimendong, indicating that soil nitrogen-fixing bacterial responded differently to the process of bamboo invasion of broadleaf forest. The results of cluster analysis and PCA based on DGGE bands information showed that community structure of nitrogen-fixing bacteria appeared greater shift(P<0.05) with the process of invasion. The nifH genes abundance of soil nitrogen-fixing bacteria(based on Quantitative PCR)was significant greater(P<0.05) in Moso bamboo than those in broadleaf forest in Meishan, the opposite was true for those in Shimendong and Qinglongshan, indicating different reaction of nifH gene to bamboo invasion of broadleaf forest.