Growth, anatomy, and gas exchange of Cenostigma pluviosum cultivated under reduced water levels in iron mining tailings

Purpose: Dam failures release tons of mining tailings into the environment, and these kinds of disasters have increased in recent years. For instance, a major failure occurred in Brazil in 2015 at the Fundão dam located in the Mariana city. This event released iron mining tailings for hundreds of kilometers. Because the tailings completely covered the soil in these regions, this study aimed to investigate the effects of reduced water supply in this substrate on the growth, ecophysiological, and anatomical traits of Cenostigma pluviosum, a native species with potential for use in reforestation systems. Methods: Mining tailings were collected from areas 4 km away from the dam failure location, and the contents of nutrients and potentially toxic elements as well as diameter of the tailing particles were measured. Cenostigma pluviosum seeds were germinated directly in the tailings and the seedlings were irrigated at conditions of maximum water holding capacity (HC) and 50% of this capacity (50% HC) for 40 days. Growth, gas exchange, water status, and leaf anatomical parameters were evaluated. Results: Mining tailings contained macro and micronutrients for plants, but Pb, Cd, Cr, and Al were also detected. Particle size of the tailings was small at 1.12 µm diameter. Water limitation caused no significant changes in growth parameters. Moreover, 50% HC elicited no effect on photosynthesis, but reduced transpiration and stomatal conductance. The 50% HC treatment increased stomatal density but had no effect on stomatal size. Leaf tissues became thinner in plants under 50% HC. Conclusion: Mining tailings from Fundão dam failure induced no toxicity in C. pluviosum plants and a reduction in water availability did not cause water stress, thereby favoring reforestation systems. Similar species may perform equally well with tailings from iron mining industry showing equivalent traits.