Respostas ecofisiológicas de espécies arbóreas nativas em área afetada por rejeito de minério de ferro na bacia do Rio Doce

Abstract

After the collapse of the Fundão dam, a large amount of iron ore tailing was released into the Doce River basin, causing suppression of vegetation typical of the Atlantic Forest and contamination of soils with trace metals, such as Mn and Fe. The use of native species tolerance and appropriate fertilization techniques, with less economic and environmental impact, are steps to be considered in the decision-making process for the recovery of affected areas. The objective of this study was to determine the physiological bases that contributed to the tolerance of tree native species to the Atlantic Forest in an area affected by Fundão tailing and under fertilization conditions. The development of pioneer (Anadenanthera colubrina, Bixa orellana and Peltophorum dubium) and secondary species (Cedrela fissilis, Handroanthus impetiginosus and Handroanthus serratifolius) was monitored for 35 months since planting. During the sampling period, the survival, growth and nutritional status of the species in tailing were evaluated. At 5 months of planting, the photosynthetic capacity and oxidative metabolism of six species growing under different fertilization conditions [inorganic and organic fertilization (inoculum composed by beneficial microorganisms) and combined treatment (fertilizer and inoculum)] were investigated. After 16 months of experiment, the morphophysiological mechanisms that contributed to the better performance of B. orellana, P. dubium and H. impetiginosus in tailing fertilized with inorganic compost were investigated. For this, were realized morphological (iron histolocalization and determination of leaf thickness) and physiological evaluations [nitrogen and phosphorus remobilization, chlorophyll a fluorescence, photosynthetic efficiency, gas exchange, water efficiency, photosynthetic pigment content, specific leaf area and oxidative metabolism (H2O2, MDA, antioxidant enzymes)]. The results showed that the fertilization treatments promoted the nutritional quality of the newly established species in the tailings, with inoculation being a viable alternative to inorganic fertilization. Furthermore, the performance of pioneer species was correlated to the highest leaf nitrogen content and photosynthetic efficiency, while the performance of secondary species was modulated by the high concentration of iron in the leaves. The species invested in antioxidant protection to control cellular oxidative damage, and only C. fissilis showed lower photosynthetic efficiency. In the long term, the plants tolerance response did not reflect successional classification. A. colubrina, C. fissilis and H. serratifolius showed low performance in the field, which may be related to the compaction and high iron concentration of the substrate. The good performance of P. dubium was associated with greater photosynthetic efficiency, intense energy allocation to carbon metabolism and greater biomass production. B. orellana, by locating iron mainly in the palisade tissue, invested in antioxidant protection (enzymatic and non-enzymatic) to maintain photosynthetic efficiency. H. impetiginosus hyperaccumulated iron in the leaves and carried out intense energy dissipation through non- photochemical means and activation of antioxidant mechanisms, thus maintaining its photosynthetic rate and growth in the tailing. Different ecological and morphophysiological adjustments contributed to the persistence of native trees in the impacted area. Thus, we now indicate both the pioneer and secondary species evaluated for use in rehabilitation projects in areas degraded by iron mining tailing.