Beneficial effects of commercially available preparations of humic substances and mycorrhiza on growth and photosynthesis of sorghum and hemp cultivated on a metal(loid)-polluted field

Metal pollution in agricultural soils threatens global food security and reduces both the yield and quality of crops cultivated for non-food purposes. Biostimulants can support plant growth in such soils by mitigating the effects of pollution and enhancing biomass production. However, the mechanisms underlying the beneficial effects of biostimulants remain poorly understood. The effects of humic substances (HS) alone or in combination with mycorrhiza (HS + M) on the growth, metal accumulation, photosynthesis, and selected stress markers in hemp (Cannabis sativa L.) and sorghum (Sorghum sudanense x bicolor) grown in a field polluted with Zn, Cd, Pb, and As was investigated. Application of HS significantly increased the shoot fresh weight of both crops. However, only in sorghum was this increase correlated with higher CO2 assimilation rates, water use efficiency, and chlorophyll content. In general, chlorophyll fluorescence parameters remained unchanged in plants treated with biostimulants, indicating that the light phase of photosynthesis was unaffected. Similarly, no significant effects were found on the mineral profile, including pollutant concentrations, or lipid peroxidation levels (as a stress marker). PCA analysis revealed a higher level of lipid peroxidation in hemp, which was positively correlated with the contents of flavonols, anthocyanins, and sugars – components likely involved in oxidative stress mitigation. The application of biostimulants, specifically HS, represents a promising approach for improving crop yield and quality on metal(loid)-polluted agricultural soils, with potential implications for more sustainable agriculture and ecosystem services.