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.

Fertilization during mineland rehabilitation may shift competitive outcomes toward invasive species

“…To increase the environmental performance of rehabilitating areas, additional native species have been explored for this purpose ). Due to their high abundance in canga ecosystems and high biomass production, the grasses Axonopus longispicus and Paspalum cinerascens (Viana et al 2016) have been indicated as suitable candidates for rehabilitation efforts (Caldeira et al 2021;Boanares et al 2023).…”

“…Traditional rehabilitation management involves the planting or seeding of species (e.g. Ramos et al 2019;Caldeira et al 2021;Maciel et al 2023;Boanares et al 2023;Massante et al 2023) and relies on fertilization to maximize vegetation growth. This procedure frequently confronts challenges from invasive species infiltrating early in the rehabilitation process (Weidlich et al 2020b;Torres et al 2021), and control measures for invasive species, such as chemical and manual weeding, often demonstrate limited long-term success due to reinvasion (Pearson et al 2016;Weidlich et al 2020a).…”