Research On Response To Low Cadmium Stress Under Arbuscular Mycorrhizal Fungi-Rice Symbiosis

In China cadmium pollution incident occurred in a large area of farmland has become a major safety hazard in rice production. To investigate the use of biological fixation in low cadmium contaminated soil situ application and safe production of rice, a pot experiment was conducted to analyze the effect of arbuscular mycorrhizal fungi(AMF) on rice growth index, physiological index, rhizosphere microbial communities and cadmium content of various rice organs under low cadmium contamination conditions. Furthermore the effect of arbuscular mycorrhizal fungi on arbuscular mycorrhizal fungi- rice symbiosis in low cadmium pollution was analyzed.After innoculated of AMF inoculum in the low cadmium contaminated soil, the average root colonization rate of rice reached 27.31 ± 4.25%. AMF and rice formed a good and stable symbiotic relationship. The mycorrhizal dependency index of host plant reached 120.43%. AMF colonization can promote the expansion of the underground plant organs and increase the absorption and adsorption capacity of the root system. With AMF colonization, growth index including plant height, root length, and shoot ratio was higher than that of non- colonization rice plants. Especially, the root to shoot ratio increased as 22.37%. With increased rice root proportion, underground organs were more likely to expand and enhance the plants adsorption and absorption of elements. Innoculation of AMF inoculum can significantly increase biomass of rice nutrition organs. Campared to CK group, the average increase rate of biomass of GM group was 29.76%, and the average increase rate of the seed yield of GM group was 12.61%.With the increase of light intensity, the net photosynthetic rate of rice plants increased quickly at the beginning, then increased slowly, and eventually leveled off. With the increase of soil cadmium content, net photosynthetic rate of rice plants were decreased with various degrees. It indicated that low cadmium pollution stress caused a significant inhibition in net photosynthetic rate of rice leaves. MDA content in rice roots increased with increasing cadmium content. It indicated that low cadmium stress caused damage on the environment within the rice cells. However, innoculation of AMF can reduce the MDA content and increase SOD and POD content in the rice roots. That means innoculation of AMF relieved a certain extent peroxidation of the rice plant cell membrane lipid.High-throughput sequencing technology was applied to analyze the microbial community structure of AMF- rice symbiosis rhizosphere in low cadmium contamination conditions. It found that the fungal microbial diversity of treated group(GM) with AMF innoculation was significantly higher than that of the control group(CK). It indicated that innoculation of AMF significantly improved fungal microorganisms community abundance and diversity in the rice rhizosphere in low cadmium polluted soil.With AMF innoculation, cadmium content in rice root was higher than that of non- innoculation with various degrees. And with AMF innoculation,the cadmium content in stems and leaves was lower than that of non- innoculation. It indicated that AMF innoculation increased the rice root fixation capacity of the heavy metal cadmium in the soil, while weakened the transport of cadmium in the soil from root to stem and leaves. Soil cadmium content safety threshold of the national food safety standards of rice grains production increased from 0.20 mg·kg-1 to 0.32 mg·kg-1 with AMF innoculation, which has a very important meaning for the situ use of low cadmium contaminated soil and the safety production of rice.