Arbuscular mycorrhizal fungi mitigate the negative effects of straw incorporation on Trifolium repens in highly Cd-polluted soils

Arbuscular mycorrhizal fungal (AMF) and straw incorporation may influence cadmium (Cd) status in soils and plants. Therefore, the objective of this experiment was to explore the influences of Cd addition (0, 10, 20 and 50 mg kg(-1) soil), arbuscular mycorrhizal fungal (AMF) inoculation (without or with mycorrhizal inoculation), rape straw residue application (0 and 0.8% w/w) and their interactions on the plant performance and element absorption of Trifolium repens and soil enzyme activities in Cd-contaminated soils. When the Cd addition rate was less than 20 mg Cd kg(-1), mycorrhizal inoculation significantly promoted plant biomass, shoot height, chlorophyll contents regardless of whether straw incorporation occurred. In the high-Cd-addition group (50 mg Cd kg(-1)), compared with treatments without straw incorporation, straw incorporation significantly decreased plant biomass, chlorophyll contents, shoot P and K concentration in the absence of AMF. On the other hand, in the presence of AMF, straw incorporation significantly promoted plant biomass and P concentration and reduced the plant Cd concentration in the 50 mg Cd kg(-1) addition treatments. Straw incorporation also significantly increased catalase, urease, p-glucosidase and acid phosphatase activities in the 50 mg Cd kg(-1) addition treatment group. The maximum acid phosphatase activity occurred in the treatment combining mycorrhizal inoculation and straw incorporation in the 50 mg Cd kg(-1) addition treatment. It was concluded that the promotion of acid phosphatase activity and P uptake and the reduction in Cd toxicity via a dilution effect could help alleviate the negative effects of straw incorporation on the growth of T. repens in highly Cd-polluted soils.