Microbial Characteristics And Functions And Their Influencing Factors Of Rhizosphere Soil Of Four Plants In The Caka Salt Lake Area Of Qinghai,China

Soil salinization and alkalization have become a worldwide resource and ecological problem.High salinity and alkalinity interfere with soil quality and vegetation growth,leading to large-scale degradation of forests and grasslands,and seriously affecting regional agricultural production and ecological construction.Therefore,the restoration of soil and vegetation,as well as the improvement of the ecological environment in saline-alkali areas,is urgent.Soil microorganisms are the most active components in soil,and their metabolism and turnover are important links in the biogeochemical element cycle process,which are of great significance in maintaining the function and stability of soil ecosystems.Metabolically active microorganisms in saline-alkali environments are of great interest due to their unique physiological and ecological characteristics and their potential application in bioremediation.It is necessary to better understand the adaptive and functional properties of microorganisms in saline-alkali environments for bioremediation.However,there is still a lack of in-depth understanding of the microorganisms with specific functions and their driving factors in saline-alkali soils.Based on this,this study selected the rhizosphere soil of four dominant halophytic plants in high-altitude saline-alkali grasslands,including Nitraria tangutorum Bobr.（NT）,Kalidium foliatum（Pall.）Moq.（KF）,Salicornia europaea L.（SE）and Achnatherum splendens（Trin.）Nevski（AS）.Through field investigation,sample collection and indoor measurement,the changes in soil enzyme activity,rhizosphere microbial carbon,nitrogen and phosphorus cycling functional gene abundance of different plants were analyzed,as well as their relationship with environmental factors.This provided further understanding of the functional potential and influencing factors of rhizosphere microorganisms in saline-alkali environments.The main results are as follows:（1）There are certain differences in the basic physicochemical properties of different plants and their rhizosphere soils.There are species differences in the content of plant organic carbon（PSOC）,total nitrogen（PTN）,and total phosphorus（PTP）in the aboveground and underground parts of plants;The mass fractions of starch（ST）,soluble sugar（SS）,and non-structural carbohydrates（NSC）significantly decreased with changes in shrubs（NT）,undershrub（KF）,and herbs（SE and AS）.The content of available nitrogen nutrients（NO₃^--N,NH₄⁺-N,and AN）in rhizosphere soils of different plants varied significantly,and the availability of nitrogen in KF and SE rhizosphere soils was greater than that in NT and AS.（2）There are significant differences in the enzyme activities of soil C-,N-,and S-cycle-related among different plants.The activities of C-（BG,AG,GAL,CBH and XYL）and N-cycle-related enzymes（LAP,ALA and NAG）were higher in KF and SE soils,while the activity of S-cycle-related enzyme（SUL）was higher in NT and AS soils.The content of available nitrogen was the main drivers for the change of soil enzyme activity.The activities of C-,N-cycle-related enzymes and oxidation enzymes（PO and CAT）were significantly positively correlated with available nitrogen,but S-cycle-related enzyme was significantly negatively correlated with them.In addition,soil salt content（SSC）,electrical conductivity（SC）,and p H have significant negative effects on soil oxidation enzyme activity.（3）Plant species have a certain impact on the carbon cycle process of rhizosphere microorganisms.There are significant differences in the enzyme abundance that partially degrade starch（glucoamylase）,hemicellulose（beta-mannosidase and beta-xylosidase）,and cellulose（cellulase）in the rhizosphere soil of the four plants,which are generally lower in NT soil,indicating that the carbon decomposition potential of rhizosphere microorganisms of N.tangutorum was weak.The Calvin cycle（M00166）and DC/4-HB cycle genes were the highest in SE soil,indicating that the rhizosphere microorganisms of S.europaea had a strong carbon fixation ability.The methane metabolism gene（acs）was the highest in NT soil and significantly higher than KF and SE.Correlation analysis showed that the abundance of carbon cycle functional genes was significantly correlated with SSC,SC,soil nutrients,and soil enzyme activity.（4）Plant species affect soil microbial ammonification and nitrate reduction processes.The abundance of gdh A（ammoniation related gene）is the highest in KF soil;the nir B and nrf A（dissimilatory nitrate reduction related genes）were higher in KF and SE soils,which was mainly due to lower SUL activity;the nir A（assimilation nitrate reduction related gene）was higher in NT and KF soils.The mantel-test results showed that the microbial nitrogen cycle metabolism process was significantly correlated with soil physicochemical properties（SSC,SC,TN,TP,SOC,WOC and AN）,soil enzyme activities（SUL,ALP and PO）,and plant factors（PTP,SS,ST and NSC）.（5）The effects of plant species on the abundance of phosphorus cycling functional genes in rhizosphere microorganisms are complex.The relative abundance of ugp Q（organic phosphorus mineralization related gene）was the highest in AS soil;the relative abundance of ppa,ppk1 and ppx（inorganic phosphorus solubility related genes）were lower in SE soil;the relative abundance of phn D/E and pst B/C（phosphorus transport related genes）were higher in KF or SE soils;the relative abundance of pho R（phosphorus deficiency response regulatory related genes）was the highest in NT soil.Correlation analysis and mantel-test results showed that the potential of microbial phosphorus cycling function was influenced by both soil factors（physicochemical properties and enzyme activity）and plant factors（plant nutrients and non-structural carbohydrates）.In summary,rhizosphere microorganisms of different halophytes in saline-alkali environments have different functional advantages.Plants mainly change the functional potential of microbial metabolism by influencing rhizosphere soil characteristics.Overall,the rhizosphere soil quality,enzyme activity,and microbial activity and function are better in K.foliatum and S.europaea.Therefore,the use of microbial driven KF and SE for vegetation restoration may be an effective measure for saline-alkali land improvement.