| Due to climate change and human activities,the alpine grassland in the ThreeRiver Source Region,Tibetan Plateau is degraded,and the poisonous weeds spread,formed a large area of poisonous weed vegetation.Studies have shown that the interaction between plant roots and soil microbes is essential for plant adaptation.Compared with forages,does poisonous weeds have stronger effects on rhizosphere microbes through root exudates,promoting its spread in degraded grasslands? In order to answer this question,the rhizosphere soils(R2)of five poisonous weeds were collected in “Black Soil Beach” and bald patches,and four poisonous weeds and two forages from different habitats were selected to collect rhizosphere soil(R0)closed to the root and root exudates.Biolog Eco plate culture and amplicon sequencing(16S and ITS)were used to study the metabolic and community structure of microbial communities,respectively.Liquid chromatography-mass spectrometry(LC-MS)was used to identify components of plant root exudates.Finally,the microbial community structure and root exudates composition of rhizosphere soil in different species and habitats were studied by network analysis,and correlation analysis was carried out.The results are as follows:(1)All microbial communities prefer to use esters,amino acids and amine carbon substrate.Compared with habitat soil,the microbial community-level carbon metabolism activity and diversity,the utilization ratio of carbohydrate carbon sources and the relative abundance of Proteobacteria increased in rhizosphere soil,while α diversity decreased.In the rhizosphere range(R2)of about 2 mm from the root,the network connectivity of the fungus is higher than that of the bacteria,but in the rhizosphere soil(R0)close to the root system,the fungal network connectivity is reduced,and the bacterial network connectivity is increased.(2)The microbial community structure in different habitats was different.The rhizosphere microbial α diversity of each plant in artificial grassland was higher than that of other degraded habitats.The rhizosphere microbial community structure of Pedicularis kansuensis and Elymus nutans was similar.In artificial grassland and degraded meadow,plant growth-promoting bacteria such as Nitrospirae and Bacilli are accumulated in the rhizosphere of Ligularia virgaurea.Different plants are significantly associated with different microbial modules,and there are more microbial modules associated with L.virgaurea than other plants.(3)The structure of root exudates of different poisonous weeds is different,and E.nutans is similar to that of Kobresia pygmaea.Compared with poisonous weeds,E.nutans exudates components are less.L.virgaurea in different habitats were significantly associated with different exudates modules,indicating that the dominant root exudates of different species in different habitats were different.(4)The correlation between root exudates and rhizosphere microbes of L.virgaurea in various habitats is extremely high,especially in bald patch.Followed by the other poisonous weeds,that of E.nutans and Kobresia pygmaea are weaker.The root exudates of Aconitum pendulum are highly correlated with rhizosphere bacteria.In conclusion,in the degraded alpine grassland of the Three-River Source Region,the direct or indirect interaction between the root exudates of the poisonous weed plants and the rhizosphere microbes is strong compared with the forages.Poisonous weeds secrete different root exudates in different habitats to interact with soil microbes,promoting its spread in different habitats. |
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