Effects Of Eco-stoichiometry On Rhizosphere Microorganisms Under Different Vegetation Type In Gully Region Of The Loess Plateau

The rhizosphere is the place where plant roots and rhizosphere microorganisms interact.Rhizosphere microorganisms provide nutrients to plants by decomposing litter and activating minerals in the soil.When soil available nutrient is low,there might be competitive between rhizosphere microorganisms and plants,and affect the function of the ecosystem.The research about the impacts of nutrient limitation on rhizosphere microorganisms are helpful to understand the metabolic mechanism of rhizosphere microorganisms and realize the effective utilization of soil nutrients.Four main vegetation types,natural succession land,Pinus tabuliformis?PT?,Armeniaca sibirica?AS?,and Robinia pseudoacacia?RP?plantations were chosen.The study mainly investigated the effects of vegetation types on the dynamics of rhizosphere microorganisms and analyzed the relationship between microbial communities and nutrient limitation.The main results are as follows:?1?Vegetation types had significant effects on the physicochemical properties of rhizosphere soil,except soil bulk density.The highest organic carbon,total nitrogen and N:P ratio were observed in the natural succession land with 20 years?P<0.05?.The content of organic carbon was 2.66 times higher than P.tabulaeformis,1.54 times higher than A.sibirica and 2.41 times higher than R.pseudoacacia.The total nitrogen content under P.tabulaeformis,A.sibirica and R.pseudoacacia was decreased by 57.78%,41.67%,55.56%,respectively,compared with the natural succession land with 20 years.The N:P ratio in the natural succession land with 20 years was 2.71 times higher than P.tabulaeformis,1.76times higher than A.sibirica and 2.29 times higher than R.pseudoacacia.?2?Vegetation restoration types had significant effects on the activities of?-1,4-N-acetylglucosaminidaseand?-1,4-glucosidase.Theactivityof?-1,4-N-acetylglucosaminidase in the natural succession land with 20 years was the highest,which was 3.33 times higher than P.tabulaeformis,1.70 times higher than A.sibirica and2.74 times higher than R.pseudoacacia.The activities of?-1,4-N-acetylglucosaminidase in the natural succession land with 20 years and R.pseudoacacia plantation were significantly higher than others?P<0.05?.However,vegetation restoration types had no effect on the phosphatase activity.?3?Proteobacteria,Actinobacteria and Acidobacteria were dominant bacterial phyla at all sites.The dominant fungal phyla were Ascomycota and Basidiomycota.The shannon diversity of shrub layer,?-1,4-N-acetylglucosaminidase,herb biomass and dissolved organic carbon were main factors that influenced the bacterial communities.The fungal communities were influenced by ln?NAG?:ln?AP?.?4?The nitrogen contents under different vegetation types could meet the growth of plants and rhizosphere microorganisms.The content of phosphorus in the soil of A.sibirica plantation was abundant,which could meet the growth of the plants and rhizosphere microorganisms.There were significant correlations among Onygenales,Crossiella,and threshold elemental ratio(TER_C:N),that indicated the Onygenales and Crossiella were the key flora to regulate the rhizosphere microbial nitrogen cycling.There were significant correlations among Hygrocybe,MND1,SBR1031,Subgroup-7,and TER_C:P,indicated the Hygrocybe,MND1,SBR1031,and Subgroup-7 were the key flora to regulate the rhizosphere microbial phosphorus cycling.