Changes in diversity,composition and assembly processes of soil microbial communities during Robinia pseudoacacia L.restoration on the Loess Plateau,China

Robinia pseudoacacia L.(RP)restoration has increased vegetation cover in semi-arid regions on the Loess Plateau of China,but ecological problems have also occurred due to RP restoration,such as reduced soil moisture.Further,it is still uncertain how microbial diversity,composition and assembly processes change with RP restoration in semi-arid regions.Therefore,amplicon sequencing of small subunit ribosomal ribonucleic acid(16S rRNA)and internal transcribed spacer(ITS)genes was performed to study soil bacterial and fungal diversity,composition and assembly processes at four study sites with different stand ages of RP plantations(Y10,RP plantation with stand ages less than 10 a;Y15,RP plantation with stand ages approximately 15 a;Y25,RP plantation with stand ages approximately 25 a;and Y40,RP plantation with stand ages approximately 40 a)along a 40-a chronosequence on the Loess Plateau.The diversity of soil bacteria and fungi increased significantly during the restoration period from 10 to 15 a(P<0.05).However,compared with Y15,bacterial diversity was lower at Y25 and Y40,and fungal diversity remained stable during the restoration period between 25 and 40 a.The relative abundances of Proteobacteria and Ascomycota increased during the restoration period from 10 to 15 a.Conversely,after 15 a of restoration,they both decreased,whereas the relative abundances of Actinomycetes,Acidobacteria and Basidiomycota gradually increased.The variations in soil bacterial communities were mainly related to changes in soil total nitrogen,nitrate nitrogen and moisture contents,while soil fungal communities were mainly shaped by soil organic carbon and nitrate nitrogen contents.Bacterial communities were structured by the heterogeneous selection and stochastic process,while fungal communities were structured primarily by the stochastic process.The RP restoration induced an increase in the relative importance of heterogeneous selection on bacterial communities.Overall,this study reveals the changes in microbial diversity,community composition and assembly processes with RP restoration on the Loess Plateau and provides a new perspective on the effects of vegetation restoration on soil microbial communities in semi-arid regions.

植被恢复和覆土厚度对砒砂岩区土壤水分及养分的影响

[目的]研究植被恢复对砒砂岩区土壤水分和养分的影响状况,明确对于砒砂岩地区土壤保水保肥效果最佳的植被恢复类型,为砒砂岩区的生态修复和区域水土流失治理提供理论依据。[方法]选取准格尔旗暖水乡裸露砒砂岩向覆土砒砂岩过渡区域,以黄土—砒砂岩交界带不同人工恢复植被和自然恢复草地的土壤为研究对象,测定土壤水分和养分含量,分析不同植被恢复和覆土厚度对砒砂岩区土壤水分和养分特征的影响(其中天然草地作为对照)。[结果]①裸露砒砂岩向覆土砒砂岩过渡区域土壤水分含量主要受黄土厚度影响,黄土的持水性能优于砒砂岩土壤,养分含量主要受植被恢复类型影响;②研究区土壤各指标均属于中等变异程度,其中土壤水分、碳、氮含量自北向南随覆土厚度增加逐渐增加,磷素分布则相反;③对比天然草地,沙棘和油松恢复对砒砂岩区土壤碳、氮含量的提升效果最好,土壤有机质含量分别提高了43.12%和34.27%,全氮提高了78.95%和42.11%,铵态氮提高25.64%和46.15%,硝态氮提高69.44%和42.22%。其中油松恢复下土壤水分含量高于天然草地54.55%,但人工植被恢复后的土壤磷素水平并没有提升。[结论]黄土较砒砂岩土壤持水能力更好,二者界面对水分下渗以及下层水分向上损失起到一定阻挡作用,因此砒砂岩区土壤水分改善方面可以考虑覆土层的蓄水保水能力。在进行人工植被恢复时,推荐种植沙棘和油松,可提升区域土壤水分、碳、氮含量,保水保肥能力较好。