| Stellera chamaejasme L.is a widely distributed noxious weed in degraded grasslands in northern China,its expansion has hampered the sustainable development of the animal husbandry.The soil microbiome is a key factor in driving nutrients cycling and maintaining the health of soil functions in grassland ecosystems,but the microbial community structure and functional turnover during the S.chamaejasme expansion,as well as its mechanism of soil nutrient cycling induced by the interaction between microbial community and S.chamaejasme are still unclear.In this study,soil samples were collected at soil depths of 0-10 cm,10-20 cm and 20-30 cm,respectively,from grassland soils with 0%,30%,50% and 70% S.chamaejasme coverage in Inner Mongolia Autonomous Region,China.High-throughput sequencing and quantitative PCR were used to analyze the soil microbial community composition and diversity,physicochemical factors,and the abundance of carbon,nitrogen,and phosphorus nutrient cycling related genes,and to clarify their interactions among factors and the effects of S.chamaejasme expansion on the grasslands ecosystem.In addition,the effects of S.chamaejasme root allelochemicals on different forage grasses in pot experiments and the effects of S.chamaejasme soil on coexisting plants were investigated.The main results were as follows:(1)By measuring soil physicochemical and soil enzyme activities,we found that S.chamaejasme expansion increased the contents of soil total carbon,soil total nitrogen,soil total phosphorus,soil nitrate nitrogen,soil water,etc.The soil p H increased slightly,and all of them were weakly alkaline.Soil β glucosidase and alkaline phosphatase activities were highest at 50% coverage,while urease activity increased significantly at 70% coverage.Genes quantitative analysis of soil carbon,nitrogen,and phosphorus nutrient cycling showed that the genes abundance of cbb L,GH3 B,nif H,nar G,nir S,ure C and pho D was lower in the 30%coverage of S.chamaejasme than that without S.chamaejasme,but increased with S.chamaejasme expansion,indicating that S.chamaejasme expansion could accelerate soil nutrient cycling and turnover.(2)Based on the analysis of bacterial 16 S r RNA gene and fungal ITS amplicons,we found that the bacterial pielou’s evenness and fungal richness showed an increasing trend with S.chamaejasme expansion.Both bacterial and fungal communities were significantly influenced by S.chamaejasme coverage and significantly correlated with soil depth.S.chamaejasme coverage had a greater effect on fungal communities than bacterial communities.Differential bacterial species were mostly enriched in 70% S.chamaejasme coverage soil,such as Sutterellaceae,Vicinamibacteraceae,Chaetomiaceae,Cordycipitaceae,Rhizobiaceae,etc.More differential fungal species were abundant than those of bacteria.(3)Through network analysis,it was found that bacterial network had high complexity and stability in soils with 50% and 70% S.chamaejasme coverage,and the key taxa,such as Sphingomonadaceae,Chitinophagaceae,and Pyrinomonadaceae,etc,had potential functions of growth promotion,disease prevention,and degradation of complex compounds.Fungal network had higher complexity and stability with more saprophytic fungi in 30% and 70%coverage soil.The cross-kingdom network was more complex and stable in the 50% coverage soil,and the proportion of negative network correlation decreased and then increased,which was consistent with the trend of soil nutrient changes.Microorganisms increased cooperation when nutrients were scarce,and the competitive exclusion effect became stronger when the nutrient content increased.(4)The correlation analysis revealed that soil depth,p H,total carbon,total nitrogen,nitrate nitrogen,urease,and β-glucosidase were more correlated with microbial communities.Microbial community diversity,differential taxa,and soil nutrients were positively correlated with nutrient cycling genes abundance.The results of structural equation models(SEMs)showed that S.chamaejasme expansion,differential taxa,and nutrient cycling genes had direct positive effects on ecosystem multifunctionality(EMF),and soil p H and water content mainly influenced EMF indirectly by affecting microbial diversity and composition.(5)The pot experiment showed that the plant height,root length,and biomass of Medicago sativa and Elymus dahuricus increased with the increase of S.chamaejasme coverage,with E.dahuricus initially accumulating more biomass than that of M.sativa.The addition of S.chamaejasme root extract significantly inhibited the root growth of M.sativa,but had no significant effect on the biomass of E.dahuricus.In conclusion,we analyzed the changes in soil nutrients,microbial diversity and cooccurrence patterns,nutrient cycling,and their interactions during the expansion of S.chamaejasme in degraded grassland in dryland,and elucidated the effects of S.chamaejasme expansion on the ecosystem.In addition,based on pot experiments,we found that E.dahuricus(Poaceae)was more tolerant to S.chamaejasme soil and root extract.This study provides theoretical guidance and practical support for the subsequent restoration of the degraded grassland. |
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