The effects of variable soil moisture on the phytoextraction of CD and ZN by brassica Juncea

Brassica juncea L. Czern and Coss is regarded as a classic hyperaccumulator in the field of phytoremediation. Countless studies have proven the versatility of this species to successfully uptake a diverse range of pollutants, even when exposed to challenging growth conditions. In spite of this, the effect of soil moisture in the species phytoextractive performance has not been explored. Considering the critical role of water for plant growth and development, three different soil moisture treatments (75%, 50%, and 25% of their soil water capacity) were applied to plants growing in soil previously polluted with 30 mg Kg^-1 and 1800 mg Kg^-1 of Cadmium and Zinc, respectively. The results revealed physiological and biochemical advantage in plants grown at 75% soil moisture (SM75), displaying higher biomass and lower hydrogen peroxide levels. In addition, the output of tests such as chlorophylls and carotenoids contents, and photochemical efficiency, suggests the species capacity to acclimate to drought stress and metal toxicity without compromising its photosynthetic activity. The metal accumulation results display no significant differences for Cd amongst the three treatments, but show a clear superiority of SM75 for the uptake of Zn. In fact, SM75 exhibits a three-fold bioaccumulation factor in comparison to 50% and 25% soil moisture treatments (SM50 and SM25). The implications of these results for phytoextraction are discussed while concluding that a higher soil moisture rate may improve the efficiency of B. juncea in the uptake of Cd and Zn.