Soil lead alters phytase activity and mineral nutrient balance of Pisum sativum

Abstract

To examine effects of lead uptake on mineral nutrient contents, Pisum sativum was exposed to 0.5–9.4 mmol lead acetate kg −1 dwt soil for 12 and 21 days in potted soil cultures in a greenhouse. Over 21 days, more lead accumulated in the shoot at the 6.5 mmol kg −1 Pb treatment than at any lower or higher soil concentrations. The tolerance index (TI) for roots displayed a linear negative relationship with soil lead. Of 11 nutrient elements assessed, only iron and copper concentrations did not change significantly during 12- or 21-days Pb exposures. Lead at a 4 mmol kg −1 soil concentration altered the constant pattern of export of major elements from the cotyledons: at day 9, they were poorer in manganese but richer in magnesium, sulphur, sodium, and zinc than were the controls. The in vivo phytase activity of cotyledons was one of the parameters changing with age; at day 12 it was 70 and 75% inhibited by 2 and 4 mmol Pb kg −1, respectively. Imbalance in mineral nutrients was thus concluded to be a major impact of lead. Some of the alterations, the parallel patterns of change identified, and the mobilisation of major elements to the top of the shoot, are suggested to represent response mechanisms, which may help explain the fairly high tolerance to lead in terms of biomass and chlorophyll contents, of this species. Sensitivity to lead changed with age and soil lead concentration, with significant effects recorded below the maximum lead content suggested for agricultural soils (500 mg kg −1).