Growth Response, Gas Exchange, and Leaf Anatomy of Handroanthus spp. Seedlings in Mine Tailings Enriched with Nutrient Solution

This work aimed to evaluate the effects of nutrient solution application on ecophysiological characteristics of Handroanthus serratifolius and Handroanthus impetiginosus cultivated in iron mine tailings. Sixty-day-old seedlings of both species were transplanted into mine tailings maintained at maximum water-holding capacity. Hoagland and Arnon’s nutrient solution was applied fortnightly as one of the treatments, and the height of the seedlings was measured weekly. At the end of the 60-day-long experiment nutrient content, growth, gas exchange, and leaf anatomy were evaluated. The experimental design was completely randomized in a 2 × 2 factorial scheme, with two species and two nutrient conditions, i.e., with nutrient solution (NS +) and without nutrient solution (NS −), with 7 replicates (n = 28). Mine tailings contained significant contents of macronutrients (N, S, Mg, P, K, and Ca), micronutrients (Fe, B, Mo, Na, Cu, Ni, Zn, and Mn), and potentially toxic elements (Cr, Pb, Cd, and Al) that were absorbed by Handroanthus seedlings. The NS + treatment increased the dry mass and the photosynthesis of H. impetiginosus alone, compared to H. serratifolius. NS + treatment reduced H. serratifolius stomatal conductance but had no effect on H. impetiginosus. Adding nutrient solution did not appreciably change the water use efficiency of either species. The diameter of the xylem vessels decreased as plant nutrient availability increased. The increase in H. impetiginosus growth is related to thicker photosynthetic tissue and a higher photosynthetic rate in mine tailings supplemented with nutrient solution. This Handroanthus species showed potential for reforestation of areas impacted by iron mine tailings, though the benefits from the application of nutrient solution will depend on the species.