Respostas fotossintéticas e anatomia foliar de Schinus terebinthifolia Raddi cultivada em resíduo de mineração de ferro e sob diferentes níveis de sombreamento

Abstract

The environmental impact caused by mining activities has increased substantially in recent years worldwide. The risk of global contamination has become a concern due to pollution from potentially toxic elements (PTEs) present in the waste from this activity. Brazil has been facing major issues due to the rupture of mining dams. In this context, phytoremediation and revegetation can be applied as environmentally safe strategies for the recovery of degraded areas. Schinus terebinthifolia Raddi (Anacardiaceae) is a pioneering tree species that has shown tolerance to mining waste and potential for the recovery of degraded areas. However, the species' level of tolerance to iron mining waste under the influence of secondary factors, such as shading, is unknown. The hypothesis of this investigation is that S. terebinthifolia is tolerant to iron mining waste, and that shading, as a secondary and natural factor during ecological succession, may affect the species' photochemical characteristics, growth, and anatomy, as well as its tolerance to the waste. The hypothesis of this investigation is that S. terebinthifolia is tolerant to iron mining waste, and that shading, as a secondary and natural factor during ecological succession, may affect the species' photochemical characteristics, growth, and anatomy, as well as its tolerance to the waste. Thus, the objective of this work is to evaluate the photochemical characteristics of photosynthesis, growth, and leaf anatomy of S. terebinthifolia grown in iron mining waste and under different shading conditions. The work was conducted in the Laboratory of Genetics and Plant Biotechnology – BIOGEN, and in the experimental area of the Santa Clara Campus, both at the Federal University of Alfenas. Plants previously produced were transferred to pots containing two types of substrates: sand or iron mining waste. The pots were maintained under three different radiation conditions: 0% (full sun), 40%, and 80% shading. The experimental design was completely randomized in a 2x3 factorial scheme, with four repetitions (n=24), consisting of two types of substrate and three shading conditions. The obtained data were subjected to the Shapiro-Wilk normality test with 5% significance. Subsequently, they were subjected to analysis of variance, with means compared using the Scott-Knott test at a 5% significance level, with the help of the Sisvar 5.0 software. All the data showed a normal distribution, and there was no significant interaction between substrate and shading for the studied variables (P>0.05). The results show that S. terebinthifolia increases the chlorophyll content under 80% shading, although it reduces the thickness of the palisade and spongy parenchyma. Shading did not promote significant differences in the quantum efficiency of photosystem II; however, it reduced the electron transport rate. The species shows good performance regarding its growth and biomass allocation to different organs and is able to acclimatize to different shading levels. Although the mining waste reduced some parameters, such as the quantum efficiency of photosystem II, there was no plant mortality, and growth was only slightly affected. Thus, S. terebinthifolia demonstrates potential for the recovery of areas degraded by iron mining waste and can tolerate different shading intensities that may occur during the succession process.