Study On The Feedbacks Of Halophytes And Microorganisms In Desert Steppe

As a transition zone between grassland and desert and an important ecological barrier,desert steppe is extremely sensitive to climate change and human activities,with scarce and high variability of precipitation,and extremely weak in soil leaching process,which leads to the obvious and widespread phenomenon of salt surface aggregation.The colonization of halophytes makes it possible to stabilize and restore the ecosystem.Halophytes are widely distributed in the desert steppe ecosystem and can resist stress through the characteristics of dilute salt,salt secretion and salt rejection.However,previous studies have focused on the physiological characteristics and molecular mechanisms of halophyte under stress,and lack of systematic research on plant-microbe interaction in halophytes.Nowadays,balancing the services and functions of desert steppe ecosystems has become a complex and challenging task.However,the maintenance strategy of endophytic microbial communities among different tissues of halophytes and the environmental factors driving the composition process of rhizosphere and phyllosphere microbial communities,the influence mechanism of halophyte litter input and root exudates on soil microbial communities,and the mechanism of halophytes feeding back the multi-function of soil ecosystem are lack of systematic and in-depth research.In view of this,we investigated the halophytes such as Kalidium cuspidatum,Nitraria tangutorum,Reaumuria songarica and Tamarix chinensis,the typical halophytes in Ordos desert steppe.And carried out field plot community investigation,Uav image analysis,laboratory control experiment,plant and soil physicochemical properties,microbial high-throughput sequencing and non-target metabolomics analysis.Combined with machine language,we systematically and comprehensively studied the microbial community structure and diversity,the network relationship between microorganisms and the regulation pathways of multi-factors on ecosystem versatility under the interaction of halophytes and microorganisms in desert steppe.The conclusions are as follows:(1)The distribution of halophytes in salt marsh of desert steppe has a spatial pattern of vegetation selforganization.Regardless of spot/patch or gradient pattern,soil physicochemical properties and halophyte types are important factors affecting the distribution of halophytes and soil microbial community structure in desert steppe.With the increase of plant coverage and the decrease of water and salt gradient,the diversity and richness of soil bacteria increased,and the composition of bacterial community tended to be random,while fungi were less affected by the change of water and salt.The cover of halophytes enhanced the interaction between bacteria and bacteria-fungi in salt marsh,which made the network relationship between soil bacteria and fungi more complex.However,the soil in halophyte shrub plot has a more stable bacterial-fungal network relationship than that in halophyte herb plot.Soil water and salinity have negative effects on salt marsh ecosystem,while halophyte coverage,soil nutrients and soil watersoluble ions have positive effects,which can all be used as predictors of the multifunctional index of salt marsh ecosystems.(2)There were differences in bacterial and fungal communities among the rhizosphere.roots,stems and leaves of different halophytes(Kalidium cuspidatum,Nitraria tangutorum,Reaumuria songarica).The dominant phyla of rhizosphere bacteria were Proteobacteria,Firmicutes,Actinobacteria,Gemmatimonadetes and Bacteroidetes.Proteobacteria and Actinobacteria were dominant in roots.Proteobacteria,Actinobacteria,Cyanobacteria,Firmicutes were dominant in stem,while Cyanobacteria and Proteobacteria were dominant in leaves.Ascomycota is the dominant phylum of rhizosphere,root.stem and leaf.The relative abundance ratio of each phylum in plant tissues was also different with different plant species.Halophytes had a selective effect on the colonization of endophytic bacteria and fungi.The diversity and richness of bacterial community decreased with the colonization process from plant rhizosphere to tissue,while the change of fungal community was not significant.The endophytic bacteria and fungi of halophytes were rich in potential growth-promoting bacteria resources.(3)The simultaneous decrease of soil water and salt content drove the transformation of rhizosphere bacterial community composition from deterministic process(homogeneous selection)to stochastic process(ecological drift)in Sophora alopecuroides.With the increase of soil water and salt,rhizosphere bacterial network of Sophora alopecuroides showed higher connectivity and complexity.The asynchronous changes of soil water and salt caused by seasonal changes reduced the diversity and richness of rhizosphere bacteria community in Reaumuria songarica,but had no significant effect on phyllosphere bacterial community.The accumulation of salt in phyllosphere reduced the relative abundance of nitrogen-fixing bacteria in leaves,while oligotrophic bacteria gradually dominated.The increase of soil salt content increased the accumulation of phyllosphere salt content in halophytes,and then increased the richness of phyllosphere bacterial community,but decreased the diversity and richness of rhizosphere and phyllosphere fungal community.Salt stress increased the connectivity and complexity of network in phyllosphere bacteria and rhizosphere fungi,while phyllosphere fungi and rhizosphere bacteria showed the opposite trend,and had niche complementary effect.When water was scarce,the connectivity and complexity of Nitraria tangutorum soil bacterial network decreased,while salt stress increased the connectivity and complexity of soil bacterial network,but decreased the stability of the network.Nitraria tangutorum can respond to drought and salt stress by secreting glycerin and increasing amino acid in root system.(4)Halophyte remediation reduced salinization of surface soil,increased the connectivity and complexity of bacterial network,and reduced the intensity of archaea network,resulting in niche competition effect.Fencing effectively improved soil physicochemical properties and increased the diversity and richness of soil bacterial community in halophytic meadow.Both halophyte afforestation and farmland reclamation increased soil carbon and nitrogen,but farmland reclamation reduced the network relationship between soil bacteria and fungi,while halophyte shrub increased the intensity of soil bacteria-fungi interaction.In conclusion,the coverage of halophyte has a positive effect on soil ecosystem function and effectively improves soil ecosystem versatility in desert steppe.This study is helpful to provide a scientific basis for deep understanding of the role in halophytes on desert steppe ecosystems under the background of global change,and to provide an important theoretical basis for the sustainable management and utilization of desert steppe.