Low fertilization optimizes the water use efficiency of an Amazonian canga grass for mineland rehabilitation

ABSTRACT The peculiar characteristics of mining waste substrates represent a significant challenge for environmental rehabilitation. Here, we evaluated the revegetation potential of Paspalum cinerascens on substrates from mining areas of Serra dos Carajás, a region harboring a large mine complex in the eastern Brazilian Amazon. Paspalum cinerascens is a native grass widely distributed in the canga ecosystem, a vegetation type covering iron ore reserves. Seeds of P. cinerascens harvested in canga were germinated in sterilized quartzite sand and the seedlings grown in controlled conditions for 90 days. The seedlings were then cultivated in canga topsoil (control, without fertilization) and mining waste substrate with half and complete fertilization currently applied at the beginning of mineland rehabilitation in Serra dos Carajás. Regardless of fertilization, plants grown in the mining waste substrate did not differ in carbon assimilation, tillering rate and root biomass, despite higher leaf nutrient content and lower root: shoot ratio when compared to plants in canga topsoil. Compared to the control, complete fertilization led to significantly taller plants, higher shoot biomass and reduced water use efficiency. Half fertilization led to higher phosphorus and water use efficiency and stomatal density. Our results confirmed that P. cinerascens has adaptive traits to grow and thrive in the harsh environmental conditions of post iron ore mining, and can be used in rehabilitation processes. Moreover, half fertilization led to plants with optimized water loss in exchange for carbon without significant costs to plant growth, an interesting trait for rehabilitation in areas experiencing water restrictions.