Responses of Nitrogen-Fixing Bacteria Communities to Elevation, Season, and Slope Aspect Variations in Subtropical Forests of Yunnan, China

Abstract

Nitrogen-fixing bacteria play a significant role in tropical forest ecosystems. However, little is known about the comprehensive effects of altitude gradient (1000–2600 m), seasons (October, January, April, and July), and slope aspects (east and west) on the abundance and diversity of nitrogen-fixing bacteria in subtropical forest. Q-PCR and PCR-DGGE methods were performed to explore the abundance and diversity of nitrogen-fixing bacteria, respectively, in the Ailao Mountain subtropical forest. Our results showed that the abundance of nitrogen-fixing bacteria was highest in October and December, whereas it was lowest in April and July. Moreover, there was no difference in the total number of soil nitrogen-fixing bacteria on the eastern and western slopes. The diversity of soil nitrogen-fixing bacteria is higher at low and medium altitudes, but lower at high and medium altitudes with increasing altitude, and similar variation in the eastern and western slopes as well. Moreover, the most influential factors affecting the abundance of nitrogen-fixing bacteria was NH4+-N and herbal coverage, while those most affecting the diversity of nitrogen-fixing bacteria were NH4+-N and NO3−-N. In addition, permutational multivariate analysis demonstrated that the season had the greatest effects on the abundance of nitrogen-fixing, whereas altitude had the greatest effects on the diversity of nitrogen-fixing bacteria. These findings provide evidence that the variation in nitrogen-fixing bacteria is affected by multiple factors (altitudes, seasons and slope aspects) in the subtropical forests of Yunnan, China.