Antioxidants in soil organic matter and in associated plant materials

Abstract

SummaryThe presence of antioxidants in soil could have a significant effect on the dynamics of soil organic matter. In this paper we report some preliminary experiments, which demonstrate that antioxidants can be extracted from soils and that the quantities vary from soil to soil. Extraction with 1.0 m NaOH was effective, and this was then used on a range of mineral and organic soils, and the antioxidant capacity of the resulting extracts was measured. The antioxidant capacities obtained were positively correlated with soil carbon contents and with the dissolved organic carbon contents of the extracts. Expressing the data per mass of soil carbon showed that the antioxidants generally decreased with depth in the soil profile, suggesting that they were subject to degradation during humification. In a follow‐up study, soil, litter and fresh plant samples were collected from 15 sites with a wide variety of vegetation types and analysed for their antioxidant capacities. The aim was to show that the antioxidant capacities in the soils were related to the antioxidant capacities of the fresh plant material and/or litter above. The antioxidant capacities of the soil samples were less than those in either fresh material or litter. While there was a significant positive relationship between the antioxidant capacities of fresh material and litter, no relationship existed between the antioxidant capacities of the soils and those of either fresh material or litter.