Methanogenesis and aerobic methanotrophy in arable soils contaminated with cadmium

Abstract

Soil is a non-renewable environment in which, depending on the prevailing O2 conditions, two opposite processes – methanogenesis and methanotrophy - may take place. The rates of the processes may result in soil acting as a sink or a source of methane (CH4). Due to agricultural practices, heavy metals may accumulate affecting soil microbial processes. We tested the effect of cadmium (Cd) contamination on CH4 emission and uptake in three mineral soils (Eutric Cambisol, Haplic Podzol, Mollic Gleysol). Additionally, in the methanotrophy study, different soil moisture levels (pF 0; 2.2; 3.2) were studied. Based on the European annual and maximum limits, soils were polluted with cadmium in four doses (per dry soil mass): 0.048 mg Cd kg−1 (and its five-fold higher value) and 3.00 mg Cd kg−1 (and its five-fold higher value). The results showed that all tested soils produced and consumed CH4. Methane production rates were not significantly changed by the presence of the cadmium (except annual five-fold Cd dose in Podzol). In methanotrophy study, soil moisture was stronger regulator of CH4 oxidation (p < 0.05) than Cd pollution which effect depended on the soil type, Cd dose and pF level. CH4 was completely consumed in Cambisol (only at pF 0 with the rate significantly different from the rates at pF 2.2 and 3.2) and in Gleysol (at pF 0; pF 2.2; the CH4 oxidation rates were significantly different among all tested moistures with annual Cd dose), but this process was delayed after the application of the higher Cd doses. Among the tested soils, only the Podzol oxidized the added CH4 under all tested moisture levels (with the rate significantly different at pF 2.2 wit annual Cd dose), while Cd addition delayed CH4 uptake as well. In the Podzol, CH4 consumption was inhibited only by the highest Cd dose at low moisture (pF 3.2).