Iron Excess and Nitrogen Deprivation Influence Photosynthetic Metabolism in Grasses Used for Mineland Rehabilitation

When planning rehabilitation in iron-ore-mining impacted areas, including species that not only tolerate excess metals but also show nutrient use efficiency is paramount. We evaluated how the interaction of nitrogen (N) deficit and high iron (Fe) supply may influence the photosynthetic and nutritional metabolisms of two iron-tolerant C4 species. Paspalum densum and Setaria parviflora were exposed to standard Hoagland’s nutrient solution (control); high Fe; N deficit; and N deficit and high Fe combined, all in nutrient solution. Under adequate N supply, Fe excess decreased N concentration in leaves of P. densum . Therefore, in P. densum , N deficit and high Fe combined increased Fe concentration in the leaves, damaging the chlorophylls, causing a decline in biomass and photochemical efficiency and activation of photoprotective mechanisms. On the other hand, despite biomass and photoprotection processes were not affected in S. parviflora , adequate N supply and high Fe increased Fe concentration in the iron plaque. Furthermore, chlorophyll degradation was higher in mature leaves of S. parviflora , which showed higher mobility of N in the leaves with a decline in photochemical efficiency. In both species, the high Fe treatment triggered diffusive limitations in photosynthesis and the adequate supply of N was crucial for optimal performance in their photochemical and carbon uptake mechanisms. Considering that in mined areas nutrient deficit and Fe excess are common, it is suggested that both grasses, but especially S. parviflora , can be used in rehabilitation plans for severely impoverished mined areas.