Variation of nifH gene diversity of soil nitrogen-fixing bacteria in Moso bamboo(Phyllostachys pubescens)plantation converted from broadleaf forest

【Objectives】 Nitrogen plays an important role in promoting the growth of Moso bamboo, the major source of nitrogen in forest soil is derived from biological nitrogen fixation. However, little is known about the impact of conversion of broadleaf forest to bamboo (Phyllostachys pubescens) plantation on changes in soil nitrogen contents and soil nitrogen-fixing bacterial community structure.【Methods】 Two plots of broadleaf forest and Moso bamboo stands with the same site condition were selected. And 4 standard areas (10 m×10 m) were chosen randomly on the northeast slope in each plot. Soil samples were collected from the topsoil (0-20 cm) and subsoil (20-40 cm) layers separately. Soil pH, organic matter, available N, available P and readily available K were analyzed. The structure and abundance of nitrogen-fixing bacterial community were measured withprimers AQER and PolF via denaturing gradient gel electrophoresis(DGGE) and qPCR based on nifH gene. Preliminary identifying of soil nitrogen-fixing bacteria was sequenced by cloning. 【Results】The results showed that compared to the broadleaf forest, Moso bamboo stands had significant higher pH, moisture, contents of available N in both topsoil and subsoil and readily available K in topsoil, while the soil available P was much lower. The DGGE profiles indicated that Moso bamboo stands had lower numbers of band and Shannon-Wiener index (H). Both cluster analysis and principal components analysis (PCA) of the DGGE profiles showed the separation of the two soils clearly, and there was little difference between topsoil and subsoil for the same treatment. The real-time PCR analysis revealed that copy number of nifH gene in Moso bamboo was higher than that in broadleaf forest. Sequencing of 14 DGGE bands isolated revealed that 13 of them were affiliated with Bradyrhizobium and 1 with Azohydromonas, with the similarities ranging from 93% to 98% in known species of Gene Bank.【Conclusions】 This results showed that the conversion of broadleaf forest to bamboo plantation decreased the diversity of nitrogen-fixing bacterial community, but increased its abundance and nitrogen contents, indicating an enhanced nitrogen-fixing ability of soil.