Nitrogen fixation in biotic crusts and vascular plant communities on a copper mine tailings

Abstract

Biological nitrogen (N) fixation is thought to be a major input of N in N-limited ecosystems. This study was set up to characterize the N2 fixation of a copper (Cu) mine tailings abandoned since 1990 in Anhui Province, China. The soil N and N2 fixation rates in six different sites including bare tailings (BT), algae crust (AC), algae-moss mixed crust (AMC), moss crust (MC), non-leguminous community (VEG) and leguminous community (LEG) were determined from August 2007 to July 2008. The total N contents of surface soil at crusted or vegetated sites were always higher than that of BT, indicating that biotic crusts and vascular plants were able to improve N accumulation of the Cu mine tailings. The nitrogenase activity (NA) levels at BT, AC, AMC, MC and VEG varied greatly between seasons, with the highest values in summer. The highest N2 fixation (1.07 g N m−2) was observed in AMC, suggesting that inoculating and cultivating AMC may be an attractive means to accelerate the restoration process of the Cu mine tailings. A significant positive correlation between the N and 15N natural abundance (δ15N) of plants revealed the importance of biological N2 fixation to plant growth on the Cu mine tailings.