Modeling Microbial Regulation of Pesticide Turnover in Soils

What limits pesticide degradation in the field? Do genetic information help to improve biogeochemical models?

Many pesticides and associated metabolites are frequently detected in soils and groundwater. Most of these substances are fully biodegradable in soil under controlled conditions in the laboratory. Under field conditions, limiting factors of pesticide degradation leading to pesticide persistence in soils remain largely unclear. This project aims to elucidate microbial and physicochemical controls of pesticide degradation by process-based modeling.
We will use gene-based biogeochemical models informed by genetic data to find improved process descriptions of pesticide degradation in soils. We will develop and apply spatially distributed models (1D-3D) to quantify the effect of the encounter/ separation between pesticide degraders and substrates on pesticide degradation at the small-scale. Model development will be done for the herbicides 2-methyl-4-chlorophenoxyacetic acid and atrazine1,2 based on the PECCAD model3,4. Sensitivity studies and scenario simulations will elucidate the impact of small-scale processes on pedon-scale pesticide degradation. This will guide deriving conceptual approaches to find improved up-scaled expressions for pesticide turnover applicable in larger-scale soil-crop models (e.g., Expert-N).

• What are the key factors of pesticide degradation in soils: Microbial factors (Energy-limited growth, enzyme or gene production) or physicochemical factors (sorption)?
• What is the role of spatial distribution of degraders and pesticides in pesticide degradation in soils?
• Which key processes and regulation mechanisms are useful for the derivation of simplified up-scaled expressions of pesticide turnover in soils?

With the project, we expect to find the key processes and factors that determine pesticide turnover and persistence in soils under field conditions. Additionally, we expect to establish a basic approach of pesticide turnover in soils that represent the implications of the heterogeneous spatial distribution of pollutants and microorganisms in soils.

• Udikoviç-Koliç, N., Scott, C. & Martin-Laurent, F. Evolution of atrazine-degrading capabilities in the environment. Appl. Microbiol. Biotechnol. 96, 1175–1189 (2012)
• Bælum, J. et al. Direct analysis of tfdA gene expression by indigenous bacteria in phenoxy acid amended agricultural soil. ISME J. 2, 677–687 (2008)
• Pagel, H. et al. Micro-scale modeling of pesticide degradation coupled to carbon turnover in the detritusphere: Model description and sensitivity analysis. Biogeochemistry 117, 185–204 (2014)
• Pagel, H., Poll, C., Ingwersen, J., Kandeler, E. & Streck, T. Modeling coupled pesticide degradation and organic matter turnover: From gene abundance to process rates. Soil Biol. Biochem. 103, 349–364 (2016)