Exogenous application of nitric oxide promotes hyperaccumulator Solanum nigrum L. performances, soil properties, and microbial community in cadmium contaminated soil

Cadmium (Cd) contamination in agricultural soils poses a serious threat to food security and human health. Nitric oxide (NO), as redox-related signaling molecule, is known to promote plant growth and regulate soil quality in heavy metal-contamination soils. However, the regulatory mechanisms of NO in plant physiology and soil biochemistry have not been well-demonstrated. In this study, we investigated the role of exogenous application of sodium nitroprusside (SNP) as an NO donor additive on the growth performances, Cd accumulation and translocation, physiological biochemical response of plant, soil physicochemical properties, and soil microbial communities of hyperaccumulator Solanum nigrum L. in Cd-contaminated soil. Our results showed that 100 and 200 μmol·L−1 NO addition markedly increased the plant biomass by 16.22 % and 14.85 %, and enhanced the Cd accumulation by 46.91 % and 22.08 % in S. nigrum compared to the 100 mg·kg−1 Cd treatment alone, respectively. Moreover, NO supply could mitigate Cd phytotoxicity and oxidative damage by significantly increasing the activities of antioxidant enzymes and osmoregulatory substances content. In addition, NO addition significantly changes the soil physicochemical properties, including changed the SOC, CEC, the NH4+-N and NO3−-N contents, increased the content of soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and soil enzymatic activities, such as the 100 μmol·L−1 NO treatment increased 4.71 %, 7.45 %, 18.44 % and 29.46 % of the soil pH, EC, the content of NO3−-N and NH4+-N as compared to Cd stress alone under 50 mg·kg−1 Cd concentrations, respectively. Meanwhile, in Cd alone treatment, the soil bacterial diversity indexes were slightly increased, while the fungal diversity slightly decreased at low Cd concentrations and increased at high Cd level compared with no Cd addition groups. After NO addition, the soil bacterial and fungal diversity was enhanced compared to without NO addition. Exogenous NO treatment also significantly changed the structures of soil bacterial and fungal communities, and increased the relative abundance of soil beneficial microbial communities. Furthermore, interactions among soil environmental factors and NO addition significantly influenced dominant bacterial, and fungal taxa. These results provide proof that soil remediation with exogenous NO addition may be an effective method to improve soil microenvironment and enhance plant tolerance to metal stress.