The influence of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) on the mineralization of litter-derived alkanes and the abundance of the alkane monooxygenase gene (alkB) in the detritusphere of Pisum sativum (L.)

In the present study, the temporal and spatial variation of the abundance of the alkane monooxygenase gene alkB and 16S rRNA genes in different soil compartments was analysed in the presence or absence of 2-methyl-4-chlorophenoxyacetic acid (MCPA) after the addition of pea litter to soil in a microcosm study. Samples were analysed shortly after litter addition (T0) and 1 week (T1), 3 weeks (T3) and 6 weeks (T6) after the addition of litter. In addition also, the quantity and quality of litter-derived alkanes was analysed and measured. The results revealed a fast and complete degradation of MCPA in all compartments throughout the experiment. Nevertheless, significant changes in the distribution patterns of short- and middle-chained alkanes suggest an interaction of MCPA and alkane degradation. alkB gene copy numbers were highly influenced by the time point of analysis and by the investigated soil compartment. Overall, an increase in alkB gene copy numbers from T0 to T3 was visible in the upper soil compartments whereas a decrease compared to T0 was measured in the deeper soil compartments. MCPA addition resulted in an increase of alkB abundance at T6. Gene copy numbers of 16S rRNA were not influenced by sampling time and soil compartment. In contrast to the control treatments, a slight increase in 16S rRNA gene copy numbers was visible at T1 and T3 compared to T0 in all soil compartments.