| Ryegrasses(Lolium multiflorum Lam.)have higher ethanol conversion rate,which is a kind of high-quality fiber herbaceous energy plants.This research tried to use the plant growth-promoting rhizobacteria(PGPR)to increase the water use efficiency(WUE)of annual ryegrass(Muyao and Doarian)under cadmium stress.First,the growing characteristic of cadmium-resistant strains A02,PS08,Oj 06 and PS01 which were preserved by laboratory were tested,through measuring strains secreted ACC deaminase ability,ability of 3-indoleacetic acid(IAA),ability of iron carrier and ability of phosphate solubilisation,the results showed Oj06 and PS01 have the ability to secrete ACC ability,all strains have the ability to secrete IAA,produce iron carrier and dissolve phosphorus,but the effect is not the same.And through the plant growth promoting assay on filter paper culture for Cd-tolerant strains,after adding cadmium bacteria and inoculating plant growth-promoting rhizobacteria(PGPR),the results showed that the bud length and root length of two kinds of annual ryegrass were significantly increased(p<0.05)compared with that of single cadmium treatment.Among them,the effect of A02 and PS08 is better,so they were regard as the tested strains to regulate the water use efficiency of two kinds of annual ryegrass in the late research.Hydroponic experiment has been carried out to research the growth and water use efficiency of PGPR on two kinds of annual ryegrass(Mu Yao and Doarian)under Cd(20?mol·L-1)stress.The results showed that the toxicity of two kinds of annual ryegrass decreased after the inoculation of A02 and Ps08 under Cd stress.The biomass and cadmium content of the above and below part of the two annual ryegrasses were significantly higher than those of the single cadmium treatment,especially the cadmium content in the roots.Under the cadmium stress,after inoculating two kinds of PGPR,the root activity of the two annual ryegrasses increased dramatically,MDA content of roots and leaves was significantly reduced(p<0.05),proline content in leaves was also significantly decreased(p<0.05).At the same time,the total root length and root volume of plant roots were significantly higher than that of single cadmium(p<0.05),and the root surface area also increased.And the activities of antioxidant enzymes in the leaves of two annual ryegrasses were decreased,but the activity of the antioxidant enzymes in the roots was increased.Compared with the single cadmium treatment,the photosynthetic parameters of the annual ryegrass increased with the adding cadmium and inoculating PGPR,as a result the water use efficiency of the two kinds of annual ryegrass was improved under Cd pollution.Potting soil culture experiment was carried out with a Cd concentration of 35.29±0.15mg·kg-1.In the seedling growth stage,A02 and Ps08 strains were inoculated to the root of the annual ryegrass,without bacteria and cadmium as blank control.The results showed that the two strains had a certain effect on the growth and water use efficiency of two annual ryegrass under Cd stress.Under the cadmium stress,after inoculating two kinds of PGPR(A02 and Ps08),the biomass of shoots and roots of two kinds of annual ryegrass increased and the activity of root was significantly higher than that of Cd treatment group.Simultaneously,the content of proline in leaf and MDA content were also markedly decreased(p<0.05).And the root vigor of the two annual ryegrass was positively correlated with its water use efficiency under the same treatment.From the perspective of the cadmium content of plants,the cadmium concentration and cadmium accumulation in the shoots and roots of the two arnual ryegrasses increased when compared with the Cd control group,but did not reach significant difference.And found that the accumulation of cadmium in the shoots is higher than the roots,but the cadmium concentration in the shoots is lower than the roots.Besides,the cadmium transfer coefficient(TF)is lower than that of single Cd treatment,but the bioaccumulation coefficient(BCF)increased.May be due to the strain treatment increased the biomass of annual ryegrass,thus increasing the cadmium accumulation,but decreasing the transfer of cadmium to the ground.The photosynthesis was also improved after inoculation of two kinds of bacteria,and then increased its water use efficiency under Cd stress.The correlation analysis showed that the water use efficiency was positively correlated with net photo synthetic rate(Pn)and intercellular CO2 concentration(Ci),and negatively correlated with transpiration rate(Tr)and stomatal conductance(Gs).Thus we can increase the water use efficiency of annual ryegrass by increasing net photo synthetic(Pn)and stomatal conductance(Gs).The use of PGPR to improve the cadmium tolerance of annual ryegrass and alleviate the heavy metal poisoning in the soil,so that annual ryegrass in the cadmium pollution environment can grow well while also promote the effective use of water.The experimental results indicate that the development of energy plants on heavy metal pollution and barren land makes efficient use of water resources,and PGPR has an ideal application prospect. |
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