Rhizophagus irregularis enhances tolerance to cadmium stress by altering host plant hemp (Cannabis sativa L.) photosynthetic properties

Arbuscular mycorrhizal fungi (AMF) are widespread and specialized soil symbiotic fungi, and the establishment of their symbiotic system is of great importance for adversity adaptation. To reveal the growth and photosyn-thetic characteristics of AMF-crop symbionts in response to heavy metal stress, this experiment investigated the effects of Rhizophagus irregularis (Ri) inoculation on the growth, photosynthetic gas exchange parameters, and chlorophyll fluorescence characteristics of hemp (Cannabis sativa L.) at a Cd concentration of 80 mg/kg. The results showed that (1) under Cd stress, the biomass of each plant structure in the Ri treatment was significantly higher than that in the noninoculation treatment (P < 0.05); (2) under Cd stress, the transpiration rate, stomatal conductance, net photosynthetic rate, PSII efficiency, apparent electron transport rate and photochemical quenching coefficient of the Ri inoculation group reached a maximum, with increases ranging from 1% to 28%; (3) inoculation of Ri significantly reduced Cd enrichment in leaves, which in turn significantly increased the transpiration rate, stomatal conductance, electron transfer rate, net photosynthetic rate and photosynthetic in-tensity, protecting PSII (P < 0.05); and (4) by measuring the light response curves of different treatments, the light saturation points of hemp inoculated with the Ri treatment reached 1448.4 mu mol/m2/s, and the optical compensation point reached 24.0 mu mol/m2/s under Cd stress. The Ri-hemp symbiont demonstrated high adaptability to weak light and high utilization efficiency of strong light under Cd stress. Our study showed that Ri-hemp symbiosis improves adaptation to Cd stress and promotes plant growth by regulating the photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of plants. The Ri-hemp symbiosis is a promising technology for improving the productivity of Cd-contaminated soil.

Automated summary

Arbuscular mycorrhizal fungi (AMF) play an important role in enhancing the adaptation of plants to heavy metal stress. In this study, the effects of Rhizophagus irregularis (Ri) inoculation on the growth and photosynthetic characteristics of hemp (Cannabis sativa L.) under Cd stress were investigated. The results showed that Ri inoculation significantly increased the biomass of hemp and improved its photosynthetic performance under Cd stress. Ri inoculation reduced Cd accumulation in leaves and enhanced the transpiration rate, stomatal conductance, electron transfer rate, net photosynthetic rate, and photosynthetic intensity of hemp.