Silicon modulates copper absorption and increases yield of Tanzania guinea grass under copper toxicity

Silicon (Si) is a beneficial element which was proven to enhance the tolerance of plants to excess metal in a given growth medium. However, the efficacy of Si in mitigating Cu toxicity in plants can vary between plant species and with the amount of copper (Cu) present in the soil/medium. An experiment was performed to investigate the role of Si in alleviating Cu toxicity in Tanzania guinea grass (Panicum maximum cv. Tanzania). The experimental design consisted on complete random blocks with tree replicates containing three Si rates (0, 1, and 3 mmol L^-1) and four Cu rates (0.3, 250, 500, and 750 μmol L^-1). The grass was grown for 62 days in a greenhouse under hydroponic conditions, with a total of 36 pots. Thirteen days after sowing, seedlings were transplanted to pots and grown for further 25 days, and then exposed to the set Cu rates for 7 days. The plants were also evaluated more for 30 days after the first harvesting. The results confirmed that the Si supply to Tanzania guinea grass can alleviate the effects of excessive Cu. Plant yield increased with Si supply and decreased with the increment of Cu rates in both growth periods. Copper concentration in diagnostic leaves (DL) and in roots, and Cu content in shoots and roots were higher in plants exposed to Cu of 750 μmol L^-1 with no Si application than in other combinations. Besides reducing Cu concentration in plant tissues, the most important Si role was reducing the transport of Cu from roots to shoots, which allowed successive harvesting. Graphical abstract.