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Mathematical Model of Plant Uptake and Translocations of Organic Chemicals: Application to Experiments

Dep. of Soil Science, Oregon State Univ., Corvallis, OR 97331;
USEPA, Corvallis Environ. Res. Lab, Corvallis, OR 97333.

^* Corresponding author.

ABSTRACT

A mathematical model for uptake of organic chemicals by plants was calibrated by application to data from experiments in which the uptake of bromacil (C₆H₁₃BrN₂O₂) by soybean [Glycine max (L.) Merr.] plants was measured. The plants had been exposed to a range of bromacil concentrations at several transpiration rates. The model was initially formulated by defining a generic plant as a set of adjacent compartments representing the major pools and pathways involved in transport and accumulation of water and solutes. For this application the plant consists of one root, three stem, and three leaf compartments, with each compartment being subdivided into xylem, phloem, and storage. The model was calibrated with respect to storage coefficients that quantify rate of transport to and from storage. For calibration, bromacii concentrations measured in roots, stems, and leaves were compared with model predictions, while model parameters were changed until no further improvement in matching model prediction with experiment result was obtained. This calibration exercise revealed important plant behavior demonstrating the value of the model for elucidating plant response. The model was changed during the calibration to account for specific phenomena that occur in the roots and leaves. The information obtained was applied to results from additional experiments. Storage coefficients differed substantially between roots, stems, and leaves showing differences in plant structures and physiological functions. The coefficients generally were proportional to compartment size, independent of transpiration rate except at low concentrations and independent of concentration except at high concentrations. The model satisfactorily predicted the observed uptake and distribution patterns for bromacil in soybean plants at the stage of growth and under the environmental conditions of the experiments.