Physiological Research On Growth Promoting Rhizobacteria From Haloxylon Ammodendron Regulating Perennial Ryegrass Growth And Stress Tolerance

Drought and soil salinization are two major abiotic stress factors that constrain the global ecological environment and the sustainable development of agriculture and animal husbandry.At present,many studies have shown that plant growth promoting rhizobacteria(PGPR)can play significant roles in promoting crop yield and stress tolerance.Haloxylon ammodendron grows in harsh desert environment,which is beneficial to the survival and colonization of rhizosphere microorganisms in extreme habitat.Thus beneficial microbial resources from H.ammodendron rhizosphere have very important development and utilization values.Our research group excavated a series of beneficial rhizosphere bacteria on the basis of deep analysis of H.ammodendron rhizosphere bacterial diversity and found many PGPR strains.Perennial ryegrass(Lolium perenne L.)has high yield and good forage quality as one of the most widely used cool season turfgrass in the temperate zone of the world.However,the growth of ryegrass is severely inhibited in arid or saline environments.In this work,we used two H.ammodendron rhizobacteria strains,Bacillus subtilis strain WM13-24 and Pseudomonas sp.strain M30-35 and perennial ryegrass cultivar “Gentleman” as the materials.The commercialized PGPR strain Bacillus amyloliquefaciens GB03 was used as a positive control.We explored the physiological mechanism of H.ammodendron rhizobacteria regulating perennial ryegrass growth and stress tolerance.The main results are as follows:1.The two PGPR strains from H.ammodendron rhizosphere significantly promoted the growth of perennial ryegrass.The germination bag experiment showed that the H.ammodendron rhizobacteria suspension soaking of ryegrass seeds for 5mins significantly increased seedling root length,root surface area and root crossing number.The pot experiment indicated that H.ammodendron growth promoting rhizobacteria inoculation significantly increased the biomass,chlorophyll content,total nitrogen content,total phosphorus content and enhanced shoot GA3 content and the root IAA content.2.H.ammodendron growth promoting rhizobacteria significantly promoted the drought tolerance of perennial ryegrass.Under natural drought condition,inoculation of H.ammodendron growth promoting rhizobacteria could significantly enhance the biomass,leaf relative water content,chlorophyll content and decrease the content of MDA and relative plasma membrane permeability of perennial ryegrass seedlings.Our results indicated that H.ammodendron growth promoting rhizobacteria alleviated the damage caused by drought stress on the cell membrane and miantianed the integrity of the cell membrane and photosynthesis.3.H.ammodendron growth promoting rhizobacteria significantly increased salt tolerance of perennial ryegrass.Under 150 mM NaCl and 300 mM NaCl treatments,inoculation of H.ammodendron growth promoting rhizobacteria significantly increased seedling biomass,chlorophyll content,soluble sugar content,proline content,catalase activity and K+ content,however,decreased the leaf osmotic potential,MDA content and tissue Na~+ content.Above results suggested that H.ammodendron growth promoting rhizobacteria can enhance the osmotic adjustment,the scavenging ability of active oxygen,chlorophyll content and K+ / Na~+ ratio,thus is maintained.4.Under normal condition,the strain M30-35 in improving root surface area was better than the positive control strain GB03;the strain WM13-24 in improving root crossing number,root activity,total phosphorus content and root IAA content were better than GB03.Under drought condition,the effects of WM13-24 and GB03 on the optimization of physiological indexes were similar.Under salt stress,the effect of M30-35 on improving organic osmotica was better than GB03.The effects of WM13-24 on maintaining the relative membrane permeability and MDA content and increasing catalase activity were better than GB03.In summary,the inoculation of the two PGPR strains from H.ammodendron rhizosphere were capable of regulating endogenous hormone content of perennial ryegrass,increasing the main nutrient element content and chlorophyll content,thus significantly promoted the seeding growth and reduced a certain degree of damage caused by both drought and salt stresses.The multiple physiological indexs of the two PGPR strains in promoting growth and stress tolerance were better than those of the positive control strain GB03.This research provides new methods for the interaction of H.ammodendron growth promoting bacteria and cultivated plants as well as theoretical basis for the application of growth promoting bacteria from desert plant rhizosphere in developing the new microbe coumpund fertilizer.It also has very important theoretical and practical significance for the restoration and reconstrucon of ecological environment in desert area.