Iron mining tailings toxicity to the tolerant tree species Schinus terebinthifolia is related to leaf anatomy, photosynthesis, and growth under different pH levels

Abstract The reforestation of areas impacted by mining tailings is a growing necessity worldwide. Although there are works that investigate the tolerance of tree species to iron mining tailings, the effect of modifications in the pH of this pollutant remains unclear. This work aimed to investigate the effects of pH variation of iron mining tailings on its toxicity for the tolerant tree species Schinus terebinthifolia Raddi based on its growth and photosynthesis. S. terebinthifolia plants were grown in iron mining tailings under pH values of 4, 5, 6, and 7 in a growth chamber for 120 days, after which growth, leaf anatomy, and photochemical parameters were assessed. Plants survived in iron mining tailings, but lower pH values (4 and 5) increased the toxicity of this pollutant, significantly reducing growth as observed in seedling fresh and dry masses, the height increase, the number of leaves, and leaf area compared to pH values of 6 and 7. The severe limitation to leaf development of seedlings under pH 4 treatment prevented the evaluation of photochemical and leaf anatomy in this treatment. S. terebinthifolia under pH 5 reduced the chlorophyll content, the effective quantum yield (YII), and the maximum quantum yield (Fv/Fm) from the PSII, while significantly increasing its non-photochemical quenching compared to pH 6 and 7. S. terebinthifolia leaves showed underdeveloped chlorophyll parenchyma under pH 5, with a lower number of cells compared to pH 6 and 7. In addition, pH 6 showed higher values for leaf anatomical traits compared to pH 5 and 6. Thus, the acidification of iron mining tailings increases its toxicity by limiting chlorophyll parenchyma development, reducing the photosynthetic capacity and growth in the tolerant species S. terebinthifolia .