Application Of Plant Rhizosphere Bacteria To Promote Plant Growth Under Saline-Alkali Stress

Saline-alkali stress is one of the major abiotic stresses hindering crop growth and productivity in the world.A large number of neutral salt ions and alkaline salt ions in saline soil can cause ion deposition in the soil,leading to weaken soil fertility,and serious loss of protons around plant roots will disturb soil microenvironment.Under saline-alkali stress,the internal environment balance in plant root cells is broken,resulted in lose their normal physiological functions in the plant eventually.At present,the area of saline-alkali land is widely distributed in the world,and it is showing a trend of continuous expansion,which seriously endangers the global ecological balance,agricultural development and food security.In the past few years,a large amount of work has been carried out on improving the saline-alkali land,but there are many disadvantages in the strategies such as physical and chemical methods.Therefore,determining an effective and friendly environmental method is of great significance to the management of saline-alkali soils.At present,many studies have shown that plant rhizosphere growth promoting bacteria(PGPR)plays an important role in plant response to adversity stress.The application of PGPR can alleviate the damage caused by saline-alkali stress to plants and enhance the salt-tolerant ability of plants.It has become an efficient saline-alkali soil improvement measure.In this study,strains POD₃25 and PLD₁2-1 isolated from the rhizosphere of the halophyte Puccinellia distans located in Daqing,Heilongjiang.After strain morphology and16S r DNA sequence identification and phylogenetic tree analysis revealed that POD₃25belongs to Serratia marcescens.and the PLD₁2-1 belongs to Pseudomonas sp.The examination of the salt-tolerant ability of the two strains showed that the growth trend of POD₃25 and PLD₁2-1 strains was basically the same as the control group under different Na HCO₃,Na₂CO₃and Na Cl concentrations,the growth activity of the strains is not significantly different from that of the control group.It can be concluded that both strains have good salt-alkali tolerance.Furthermore,co-cultivation of strains and Arabidopsis can increase the germination rate of Arabidopsis seeds and the growth of roots under salt-alkali stress conditions.In addition,when the strains and plants were cultured seperately,we found that the strains produced volatile compounds which could promoted plant root development under saline-alkali stress.In tomato(Lycopersicon esculentum Mill.)and maize(Zea mays L.)planting experiment,POD₃25 and PLD₁2-1 strains can also improve the root systems growth and development in these two plants under salt-alkali stress conditions.A highly significant enhancement of the root biomass of tomato was observed after the interaction between the strains and plant.These two strains also played an essential role in promoting the maize root growth,under saline-alkali conditions,and the POD₃25 showed a more pronounced effect on maize root growth.In order to use the strain in farming,we also applied chemical fertilizers,organic fertilizers and bacterial agents on the basis of normal agricultural treatments in saline trial fields in Lijin and Kenli,Shandong.Using statistics analysis on maize agronomic trait data and yiled,we found that the strains had a role in promoting the crop production in alkaline soil.Taken together,it was demonstrated that plant rhizosphere growth promoting bacteria(PGPR),POD₃25 and PLD₁2-1 had obvious growth promoting effects on plants under saline alkaline conditions.The research of this subject is of great significance for the sustainable improvement,development and utilization of saline-alkali land resources in the future,and also provides an important theoretical basis for the development of green microbial organic fertilizers without secondary pollution to the environment.