Degradation pathways of plant protection products in floodplain soils: Impact of redox potential and nutrient availability
Soils are subjected to diverse conditions, such as heavy rainfall with temporary inundation, alterations in redox potential and nutrient fluxes. Soils are also subject to accumulation of plant protection products (PPPs). For example, floodplain soils serve as a sink (or source) to PPPs due to their high organic and clay fraction in the deposited soil. The fluctuations in redox potential and nutrient-, and PPP concentrations is particularly evident in these ecosystems. Inevitably, the degradation pathway of PPPs is likely affected by the mentioned conditions. The degradation pathways of several PPPs in soils have been described widely. Studies however on currently-used pesticides are less common. Experiments with different moisture scenarios or redox potential in the soil are even more scarce.
The aim of this project is to conduct an incubation study with particular focus on the non-extractable fraction of PPPs in soil. Incubation studies with 14C labeled PPPs hold important information on the degradation of a compound; the mineralization to 14CO2, determination of extractable residues and non-extractable residues (NERs). However, the fate of PPPs that are no longer extractable from soil is still a matter of scientific and social debate. Coupling of 14C incubation studies with 14C incorporation into microbial biomass C provides the unique chance to determine the 14C-uptake and storage of PPP residues in microbial biomass, and as such to distinguish “non-extractable residues” (NER) in “microbial NER” and “actual NER”. Furthermore, analyzing not only total microbial 14C uptake but the uptake into certain phospholipid fatty acids (PLFAs) by compound specific 14C analysis will gain insight into pathways of selected PPPs through the microbial food chain. The awareness of this potential distribution will prevent an overestimation of non-extractable residues, which are suspected to be re-suspended into the environment with time. To analyze the incorporation of PPPS into specific microbial groups under alternating redox potential, a second incubation will be conducted. The experiment will be set up to determine anaerobic/aerobic pathways and whether the microbes are exposed to substrate limitation by lack of moisture or solely by oxygen deprivation. A final incubation study will determine whether PPPs in soil can be remobilized and taken up by microorganisms as a result of root exudate priming or if PPPs can induce priming themselves.