Change in population of 2,4-D degraders in the process of 2,4-D degradation in soils under upland and flooded conditions

Abstract

The relation between the degradation rate of 2,4-D and the changes in the population of 2,4-D degraders and other microflora in soil was studied under upland and flooded conditions using two types of soils, a mineral soil in Anjo (Anjo soil, Anthrotroaquic Dystrochrept) and a humic volcanic ash soil in Mito (Ibaraki soil, Ando soil, Anthrotroaquic Dystrandept). In all cases the rapid degradation of 2,4-D started about 10 days after 2,4-D application. The degradation rate was more rapid in the Anjo soil than in the Ibaraki soil under both moisture conditions, and under upland conditions than under flooded conditions in the same soils. During the lag period the population of 2,4-D degraders increased in both soils. In the Anjo soil under upland conditions the population increased from undetectable levels to 10⁵ cells/g soil during the 30 day incubation of soil with 2,4-D. The degradation rate of 2,4-D was closely related to the proliferation rate of 2,4-D degraders. When 2,4-D was not applied to soil, the degraders proliferated at a low rate during the soil incubation. The numbers of aerobic bacteria, actinomycetes, and fungi in soil were not significantly affected by 2,4-D application. The population ratio of 2,4-D degraders to aerobic bacteria increased in the Anjo soil during the incubation unlike in the Ibaraki soil even when 2,4-D was applied.

Key Words:

• 2,4-D degraders
• herbicide
• microbial population
• soil incubation