Responses of soil denitrifying bacterial communities carrying nirS, nirK, and nosZ genes to revegetation of moving sand dunes

Abstract

Revegetation is commonly the first step to restoring degraded ecosystems in desertified regions. Large areas of plantations have been planted on moving sand dunes to control land desertification in the Horqin sandy land of Northeastern China. This method aims to recover the vegetation and improve soil nutrients thereby resulting in the change in soil microbial community and affecting soil nitrogen cycle. Denitrification is an important process of the soil nitrogen cycle. In this study, we investigated the diversities and abundances of nosZ, nirS, and nirK carrying denitrifiers in 32-year-old plantations of Caragana microphylla, Artemisia halodendron, Hedysarum fruticosum, Pinus sylvestris var. mongolica, Populus simonii, and Salix gordejevii, as well as in adjacent non-vegetated moving sand dune through clone library and real-time quantitative PCR analyses, respectively. We identified the dominant phyla of denitrifying community in the semi-arid sandy soil and determined the effects of plantation type on the soil denitrifying community. Results showed that revegetation on moving sand dunes increased the number of soil denitrifying bacteria. The structures of nosZ, nirK, and nirS bacterial communities were simple, and only one or two genera dominated the communities in the sandy soil. Pseudomonas, Mesorhizobium, and Azospirillum with the relative abundances ranged from 54.90% to 96.75%, 35.75% to 89.48%, and 58.36% to 100% in libraries, were the most dominant genus of nosZ-, nirK-, and nirS-bacterial communities, respectively, and may play important functions in soil denitrification in this area. The species diversity of nirK bacteria was relatively higher than those of the other two genes. The compositions and dominant taxa of soil denitrifying communities under different plantations were all similar to those in the moving sand dunes, and thus demonstrated that revegetation on moving sandy dune and plantation type slightly affected the compositions of nosZ, nirK, and nirS bacterial communities. However, the abundance of nosZ (ranged from 4.86 × 105 to 6.75 × 106 copies/g dry soil), nirK (ranged from 1.61 × 105 to 4.65 × 106), and nirS (ranged from 5.17 × 105 to 1.30 × 107) significantly varied with plantation type. Soil properties influenced the structures of denitrifying communities by increasing or decreasing the relative abundance of dominant taxa. Hence, the structures of nosZ, nirK, and nirS communities were affected quantitatively by plantation type and soil properties. The abundance of the three genes represents an indicator for soil denitrifying community in sand-fixation plantations.