How does drought affect native grasses' photosynthesis on the revegetation of iron ore tailings?

The revegetation of areas degraded by iron ore mining is a difficult challenge mainly due to water availability and impoverished metal-rich substrates. We sought to understand the photosynthetic responses to drought of native tropical grasses Paspalum densum (Poir.) and Setaria parviflora (Poir.) grown in iron ore tailing. The grass P. densum presented better photosynthetic adjustments when grown in the iron ore tailing and S. paviflora in response to water stress. Both species accumulated iron above the phytotoxic threshold when grown in an iron ore tailing. The net photosynthesis, stomatal conductance, transpiration, and water use efficiency decreased followed by a reduction in leaf relative water content in response to water stress for both species. The photochemical efficiency of photosystem II only decreased at the point of maximum drought. At this point, the water-stressed grass grown in the iron ore tailing presented higher H₂O₂ concentrations, particularly S. parviflora. After rehydration, full recovery of photosynthetic variables was achieved with decreased malondialdehyde concentrations, increased catalase activity, and, consequently, decreased H₂O₂ concentrations in leaves for both species. The fast recovery of the native grasses P. densum and S. parviflora to drought in the iron ore tailing substrate is indicative of their resistance and potential use in the revegetation of impoverished mined areas with high iron content and seasonal water deficit.