Recovery of Soil-Denitrifying Community along a Chronosequence of Sand-Fixation Forest in a Semi-Arid Desertified Grassland

Zhenbo Cui,Ying Zhang,Tingting Wang,Chengyou Cao,Hailong Li,Qing Ren

doi:10.3390/f12030354

Abstract

Revegetation on moving sand dunes is a widely used approach for restoring the degraded sandy land in northeastern China. The development of sand-fixation forest might improve the structures of soil microbial communities and affect soil N cycle. In the present study, the diversities of nitrite (nirS and nirK) and nitrous oxide (nosZ) reductase genes were investigated under a chronosequence of Caragana microphylla sand-fixation shrub forest (9- and 19-year), adjacent non-vegetated shifting sand-dune, and a natural forest dominated by C. microphylla. The dominant compositions and gene abundance were analyzed by a clone library technique and quantitative polymerase chain reaction, respectively. The compositions and dominant taxa of nirK, nirS, and nosZ communities under forest soil were all similar to those in the shifting sand-dune. However, the three gene abundances all linearly increased across forest age. Clones associated with known denitrifiers carrying nosZ, nirK, or nirS genes, such as members of Pseudomonas, Mesorhizobium, Rhizobium, Rhodopseudomonas, Azospirillum, and Cupriavidus, were detected. These denitrifiers were found to be abundant in soil and dominant in soil denitrification. Soil pH, total N, and available N affected the denitrifying communities by altering the relative abundance of dominant taxa. Overall, although soil attributes and forest age had no significant effects on the dominant constituents of nirK, nirS, and nosZ communities, revegetation on shifting sand-dunes facilitated the quantitative restoration of soil denitrifiers due to the increase in soil nutrients.

Highlights

The number of bacterial nosZ gene ranged from 1.01 × to 7.05 × copies/g dry soil, whereas that of the nirK and nirS genes ranged from 1.27 × 105 to 5.65 × 107 copies/g dry soil and from 5.23 × 104 to 9.14 × 107 copies/g dry soil, respectively (Figure 1)
The results showed that correspondence analysis (CCA) axis 1 and CCA axis 2 could explain 93.0 %, 86.9%, and 83.8% of the total variations in the structures of soil nosZ, nirK, and nirS communities, respectively (Figure 6)
This study suggested that the change in soil pH induced by revegetation is one of determinants for triggering the restoration of the denitrifying community

Summary

Introduction

Information on the variations in soil attributes after revegetation on shifting sand dunes is needed to assess the ecological effects and further understand the process of soil restoration along plantation development. Many studies, including the previous works of the authors, have confirmed that the artificial establishment of C. microphylla forest improves the microclimate and soil organic matter as well [4,5,6]. These favorable effects increase with plantation age [7]. Whether and how the soil microbial community under secondary barren land (shifting sand dune) can be restored via the establishment of plantations is still unknown. Several studies have utilized molecular tools or high-throughput sequencing techniques to investigate soil bacterial community under sand-fixation forests in this region [9,10,11,12,13], the response of soil-specific functional microbial groups, especially N-cycling microbes to the revegetation on shifting sand-dunes, was underestimated

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Discussion

Conclusion