[Effects of revegetation on soil nitrogen-fixation and carbon-fixation microbial communities in the Horqin Sandy...

To determine the diversity of nitrogen-fixing and carbon-fixing microbial groups in aeolian sandy soil and the effects of sand-fixation plantation type on the structures of two microbial groups in the Horqin Sandy Land, we selected six representative sand-fixation vegetations with the same age, including Caragana microphylla, Artemisia halodendron, Salix gordejevii, Hedysarum fruticosum, Populus simonii, and Pinus sylvestris var. mongolica as well as their adjacent natural Ulmus pumila open forest as test objects to investigate the diversities and structures of nifH- and cbbL-carrying microbial communities in soil by high-throughput sequencing technique. The results showed that vegetation type significantly affected soil physical and chemical properties, microbiological activities, diversities and the main compositions of nitrogen-fixing and carbon-fixing microbial communities. The diversity of soil nitrogen-fixing microbial communities under S. gordejevii and P. simonii plantations and that of carbon-fixing microbial communities under P. sylvestris var. mongolica and P. simonii plantations were significantly higher than those of other plantations. Skermanella, Bradyrhizobium, Azospirillum, and Azohydromonas were dominant nitrogen-fixation genera, with the average relative abundance of 22.3%, 21.5%, 20.8%, and 17.8%, respectively. Soil carbon-fixation microbial communities were dominated by Pseudonocardia, Bradyrhizobium, Cupriavidus, and Mesorhizobium, with relative abundance of 22.4%, 18.5%, 10.5%, and 6.0%, respectively. Soil nitrogen-fixing microbial community under C. mirophylla plantation and carbon-fixing communities under S. gordejevii and P. simonii plantations were very close to those of natural U. pumila open forest. Soil organic matter, NH₄⁺-N, and total phosphorus were the direct determining factors for nitrogen-fixing microbial community, while pH, soil moisture, and available phosphorus were main factors influencing carbon-fixing microbial community. These observations potentially provide the scienti-fic foundations for evaluating the ecological benefits of revegetation practice in sandy lands.