Effects Of Water On Root Characteristics And Rhizosphere Microbial Diversity Of Kengyilia Hirsuta

In order to study the water adaptabilited of root and the resistance mechanism of alpine forage.Kengyilia hirsuta expand from low-humid beaches to aeolian sandy sedimentary areas to form dominant communities.It is a pioneer species in the semi-humid sandy area of the southeastern edge of the Tibetan Plateau.we analysed the effects of different water stess treatments simulating with three concentration solution including 10%(severe stress),25%(moderate stress),40%(adequate moisture)on the main root morphology?root architecture?root physiological?indexes of “ Kengyilia hirsuta" seedlings growing in pot weighing control water?Six tubes of rhizosphere soil in three water gradients were taken respectively to determine the microbial diversity in 18 rhizosphere soil samples,to explore the differences of rhizosphere microbial species and structure under different water conditions,and to compare the effects of different water conditions on rhizosphere microbial diversity.The results are as follows:(1)The total root length,average diameter,root volume,root surface area,root tip and forks of Kengyilia hirsuta showed the largest at 40%,and decreasing trend with less soil water content.The root dry weight and root fresh weight were the highest in40% gradient,but the root sheath weight in 25% gradient was about 1.6 times of 10%,2.5 times of 40%,and significantly greater than 40% in 25% water gradient(P < 0.05),moderate drought stress was more conducive to the formation of root sheath.Topological indexes of plant roots in the three gradients were 0.917±0.004 a 10(10%),0.913±0.005a(25%),and 0.915±0.004a(40%).Under the three water gradients,the roots of Kengyilia hirsuta were all fishtail branches,and the fractal dimension of roots was the largest in 25%?(2)Relative electrical conductivity of roots increased significantly at 10%.Under the severe water stress,the cell membrane structure of plant roots was damaged,resulting in increased membrane permeability,increased intracellular electrolyte extravasation,and significantly increased proline as an osmotic regulator in plants.The content of SOD,CAT and APX antioxidant enzymes also increased significantly,but the POD content increased first and then decreased with the increase of soil water stress.The malondialdehyde content in plant roots was the largest in the water gradient of 25%,and the accumulation of membrane lipid peroxidation products in roots increased?(3)Under water conditions of 25% and 40%,the species diversity and species richness of bacteria were significantly greater than 10%.that is,severe water stress significantly reduced the abundance and quantity of soil microorganism.Actinobacteria,Proteobacteria,Gemmatimonadetes,Bacteroidetes and Acidobacteria were the dominant bacteria groups in three treatments.Gemmatimonas,Arthrobacter,Gemmatimonas,Sphingomonas,Pseudonocardia and Patulibacter were the major bacteria in the three gradients.Massilia was mainly present in samples of W10.6.The relative abundance of Pseudonocardia and Bradyrhizobium was the highest in the water gradient of W40.6 and W40.5.The relative abundance of Actinoplanes was the highest in the water gradient treatment of W25.5.