Arsenic fractionation and its impact on physiological behavior of sunflower (Helianthus annuus L.) in three texturally different soils under alkaline calcareous conditions

Soil textural composition may be important to control arsenic (As) behavior in soil and movement to plant. Two independent parallel experiments comprising of five As levels (0, 50, 100, 150, and 200 mg As kg^-1 soil) and three soil textural types (sandy, loamy, and clayey) were designed for determining As fractionation in soils and its consequential effects on growth, yield, and physiological characteristics of sunflower (Helianthus annuus L.). Six As fractions, i.e., NH₄Cl-extractable, NH₄F-extractable, NaOH-extractable, H₂SO₄-extractable, H₂O₂-extractable, and HNO₃-extractable, were determined. On an average, NH₄Cl-extractable As (the most phytoavailable among the extracted fractions) was 48.9, 19.8, and 6.6% of the total As while the bioaccumulation factor for root ranged between 1.9 and 9.5, 1.8 and 4.4, and 0.8 and 2.1 for sandy, loamy, and clayey textured soils, respectively. There was an increase of 8.3, 5.6, and 6.0 times in malondialdehyde with a subsequent reduction in photosynthetic rate by 53.3, 42.7, and 38.0% and achene yield 90.0, 87.1, and 85.5% in sandy, loamy, and clayey textured soils, respectively at 200 mg As kg^-1 as compared with the control. Antioxidant enzyme activities were increased with increasing As addition, and maximum activities were found at 150 mg As kg^-1, where catalase activities were 377.7, 341.6, and 292.0%; peroxidase 788.5, 758.6, and 737.0%; and superoxide dismutase 235.7, 191.8, and 177.2% higher in sandy, loamy, and clayey textured soils, respectively as compared with the control. In conclusion, As fractionation was markedly influenced by soil texture, and toxic effects of As on growth, yield and physiological characteristics of sunflower were maximum in sandy followed by loamy and clayey textured soils in descending order.