Effects Of Exopolysaccharides Of Lactobacillus Plantarum On The Growth Of Rice Seedling And Soil Environment Under Acid-cadmium Compound Stress

Cadmium is a heavy metal that poses a great threat to agricultural production,and its stress effect is affected by environmental factors such as soil physical and chemical properties.At the same time,the regulatory effect of exogenous substances on plants is also regulated by environmental factors.In order to investigate the effect of acid environment regulating cadmium on rice stress and the regulation effect of polysaccharides in this process,firstly,this study explored the effect of acid environment on the growth of rice seedlings under Cd stress,secondly,the effect of Lactobacillus plantarum exopolysaccharide on the growth of rice seedlings and soil environment under acid-Cd compound stress was explored,and the mechanism about Lactobacillus plantarum exopolysaccharide on relieving rice growth damage was explored.The main results of the study were as follows:(1)Cadmium stress has a significant inhibitory effect on the growth of rice seedlings,but weak acidic environment favored the growth of rice seedlings under cadmium stress,especially when the p H was 6.0.However,when the environmental p H decreased to 5.0,the growth of rice seedling was strongly inhibited,indicated that the acid environment intensified the inhibition of Cd stress on growth of rice seedlings.When the Cd concentration was below 0.3 mg/L,the root growth of rice seedlings(total length,surface area,diameter,total volume and root tip number)was the best at p H 6.0,and the worst at p H 5.0,and MDA content increased with the decrease of p H.Also,the results of evans blue staining test showed that the damage of rice seedling roots was strengthened with the decrease of p H under cadmium stress when the Cd concentration was 0.6 mg/L.(2)The addition of Lactobacillus plantarum exopolysaccharide significantly alleviated the damage of rice seedlings under acid-Cd compound stress,and improved the morphological indexes of aboverground and underground parts of rice seedlings.The damage degree of rice seedlings significantly reduced under acidic environment and Cd stress after adding the exopolysaccharide of Lactobacillus plantarum,moreover,it had a positive relation with exopolysaccharide concentration.The soluble sugar content of rice seedlings firstly decreased and then increased and the soluble protein content significantly increased,and the antioxidant enzyme activity and MDA content were also greatly increased under the treatment of exopolysaccharide.Meanwhile,FTIR analysis also showed that the addition of exopolysaccharide could promote the synthesis of macromolecular substances in rice seedlings,but the chlorophyll content of rice seedlings decreased under the treatment of exopolysaccharide.At the same time,the addition of exopolysaccharides could reduce the transport of Cd from underground to aboverground of rice seedlings,while the absorption and transport of Mg and Mn of hydroponics experiment showed antagonistic effect with Cd.(3)The contents of total nitrogen,available phosphorus and organic matter in soil increased after adding the exopolysaccharide of Lactobacillus plantarum,while the content of available kalium did not change significantly.Meanwhile,the activities of soil enzymes such as sucrase and peroxidase in rice rhizosphere were significantly increased with the addition of polysaccharides.The addition of exopolysaccharide significantly increased the abundance of bacteria in soil,while the OTUs is decreased under the treatment of exopolysaccharide.According to the Alpha diversity analysis,the microbial diversity decreased under the treatment of exopolysaccharide,but looked at from the species composition characteristics at the genus level between groups,the endemic species in soil increased and showed significant differences under the treatment of exopolysaccharide.In addition,the number of soil microbial enrichment species and the indicated value of indicator species significantly increased after adding the exopolysaccharide.According to the results of Beta diversity treatment,the soil community structure was obviously different,and the community function also changed along with its change under the treatment of exopolysaccharide.