Rhizophagus clarus and phosphate alter the physiological responses of Crotalaria juncea cultivated in soil with a high Cu level

• We investigate Cu tolerance and accumulation in Crotalaria juncea.
• The addition of P reduces the toxicity in Crotalaria juncea.
• Plants from the contaminated site are more efficient in controlling root Cu content.

Symbioses with arbuscular mycorrhizal fungi (AMF) may increase plant tolerance to heavy metals, in addition to the improvement in phosphorus (P) uptake by plants. This study evaluated the effects of the interaction between an increase in the soil phosphorus level and the colonization by Rhizophagus clarus on several biochemical and physiological parameters of Crotalaria juncea plants cultivated in a soil with a high copper (Cu) level. Plant growth and photosynthetic pigment fluorescence parameters, as well as the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) enzyme activities in C. juncea plants, were analyzed. The experiment was conducted in a greenhouse, and a 3 × 2 factorial design was employed, including the natural P level, 40, and 100 mg P kg−1, with and without R. clarus inoculation, with three replicates in a soil with a high Cu level (65 mg kg−1). The results demonstrate that the combination of the addition of P together with AMF inoculation improved the plant nutritional status, with consequent increases in the levels of P, K, Mg, Fe, Zn, and chlorophyll a fluorescence parameters. Furthermore, mycorrhization and phosphorus addition increased the activities of the SOD and CAT enzymes, which are responsible for the removal of reactive oxygen species when plants are exposed to high Cu levels. This synergistic effect between P application and inoculation with R. clarus could be of technological interest for achieving increased growth of C. juncea cultivated in soils with high Cu levels via the promotion of effective mechanisms for reducing Cu phytotoxicity.