Arbuscular Mycorrhizal Fungi（AMF） Community And Its Regulation On Antioxidant Enzyme In Robinia Pseudoacacia L.seedlings Under Elevated CO₂ Combined With Cd-contaminated Soil

Increasing atmospheric CO₂ concentration has become a crucial issue related to global change,additionally,heavy metal-contaminated soil is another serious environmental problem urgently needed to be solved.Arbuscular mycorrhizal fungi（AMF）can form mutually beneficial symbionts with terrestrial plants,and play an important role in enhancing the resistance of host plants to stresses.According to the challenges to human environment caused by elevated atmospheric CO₂（ECO₂）and heavy metal-polluted soils,it is important to explore the responses of AMF community to the combination of ECO₂ and heavy metal-polluted soils,and the regulation of AMF on resistance of host plant under the combination of ECO₂ and heavy metal-polluted soils,which receives little attention.In this study,AMF community characteristics in the rhizosphere soil and roots of Robinia pseudoacacia L.seedlings and the effects of AMF community on antioxidant enzymes activities in leaves were analyzed,and the regulation mechanism of AMF on antioxidant enzymes in leaves was explored in sterilized soils by inoculating the dominant genus in AMF community under elevated atmospheric CO₂（～750 ppm）combined with Cd-contaminated soil（ECO₂+Cd）using plant incubators with a precise CO₂ regulation system and pot culture method.The main results are as follows:（1）Under elevated atmospheric CO₂,the p H and DTPA-Cd content in the rhizosphere soil increased（p<0.05）,Cd content in roots decreased（p<0.05）and Cd accumulation in the whole roots increased（p<0.05）;moreover,the total Cd in rhizosphere soils and Cd content in roots decreased（p<0.05）with time and Cd accumulation in the whole roots increased（p<0.05）with time.Elevated atmospheric CO₂ stimulated（p<0.05）root biomass and root C/N ratio and inhibited（p<0.05）root N content under Cd exposure,and root S content decreased（p<0.05）at 90 days.（2）Under ECO₂+Cd,AMF gene abundance in the rhizosphere soils increased（p<0.05）relative to Cd alone,and AMF richness and diversity in the rhizosphere soils increased（p<0.05）at 45 and 135 days and decreased（p<0.05）at 90 days compared to Cd alone.Elevated atmospheric CO₂ decreased（p<0.05）AMF gene abundance and diversity in roots,and increased the relative abundance of dominant genus Glomus in roots under Cd exposure.AMF richness and diversity in roots were lower than those in rhizosphere soils.（3）The responses of soil C and p H,and root biomass,N and C/N ratio to elevated atmospheric CO₂ affected（p<0.01）AMF community characteristics in rhizosphere soils.The DTPA-Cd in rhizosphere soils and C,N,Cd content,and Cd accumulation in roots significantly（p<0.05）affected AMF community structure in roots.The relative abundance of Glomus was the greatest in both AMF community in rhizosphere soils and roots,and AMF community structure in rhizosphere soils and roots were obviously different.（4）Compared to Cd alone,POD activity in leaves decreased（p<0.05）,CAT activity in leaves increased（p<0.05）,and SOD activity in leaves significantly（p<0.05）increased at 90and 135 days under ECO₂+Cd.AMF community in roots significantly（p<0.05）affected antioxidant enzyme activities in leaves,and AMF gene abundance and the relative abundance of Archaeospora in roots significantly（p<0.05）affected SOD activity in leaves.AMF gene abundance,OTUs and the relative abundance of Ambispora in roots were the significant（p<0.05）factors influencing antioxidant enzyme activities in leaves.（5）The result of Glomus mosseae（a dominant genus in AMF community in roots and rhizosphere soils）inoculation showed that:elevated CO₂ decreased（p<0.05）the G.mosseae colonization rate in roots under Cd exposure.Under ECO₂+Cd,G.mosseae colonization in roots decreased（p<0.05）the DTPA-Cd content in rhizosphere soils and Cd content in leaves,but increased（p<0.05）the Cd accumulation in roots.Under ECO₂+Cd,G.mosseae decreased（p<0.05）MDA content and POD and CAT activities in leaves relative to Cd alone and Cd+G.mosseae and increased（p<0.05）SOD activity in leaves relative to Cd alone.Under ECO₂+Cd,G.mosseae colonization decreased（p<0.05）the expression of CAT gene and increased（p<0.05）the expression of POD gene relative to Cd alone and Cd+G.mosseae,and the expression of Cu/Zn-SOD gene increased（p<0.05）relative to Cd+G.mossese but decreased（p<0.05）relative to Cd alone.The Cd in leaves,DTPA-Cd in rhizosphere soils,G.mosseae colonization rate,and C in roots were significant（p<0.05）factors influencing antioxidant enzyme in leaves.