Plant Uptake of Chemicals with Environmental Concern

Approach, Relevance and various Testdesigns.
Plants’ uptake of chemicals in the environment, such as heavy metals and plant protection products and their degradation products, is an important dissipation process that may limit their availability for leaching, run-off and volatilisation. Beyond this the uptake of compounds of environmental concern is an important process in the context of bio-remediation and assessment of possible residues in agricultural crops.
A commonly used test protocol to access and quantify the plant uptake of environmental compounds consists in greenhouse studies involving plants cultivated without soil in nutrient solution (Hydroponics). With this test design, the water consumption as well as the corresponding mass of investigated environmental compound can be determined. Considering the variation in the test solution of both volume and concentration, plant uptake factors can be calculated. These factors range between 0 and 1, with 0 when no plant uptake occurs and 1 when a non-selective uptake happens within the transpiration flow.
In the following the characteristic of three different test designs are presented. These are used in the department EcoChemisty for the determination of plant uptake factors.
Test Design A:
Soil grown plants incubated in treated artificial soil pore water solutions
The first protocol consists of plants first cultivated in natural soil (i.e. realistic roots system development, cf. Fig. 1), and then rinsed from the full mass of soil with a gentle water shower in order to free the roots.
The plants are then transferred to the spiked solutions (cf. Fig. 2). The use of soil-free solutions allows avoiding side processes such as degradation or adsorption. Additionally, the properties of the incubation solution can be adapted to specific interests such as the pH influence on the uptake of a dissociating compound (e.g. 0.01 M CaCl2 solutions buffered on a range of pH levels).
Fig. 1: Grown roots in soil
Fig. 2: Example crops in hydroponics system
Test design B:
Perlite® grown plants incubated in treated artificial soil pore water solutions
The second protocol was developed to reduce stress sources, such as the removal of the cultivation substrate or the change of root surrounding media’s properties. The plants are here germinated in Perlite® and then further cultivated in hydroponics systems (cf. Fig. 3). The optimal cultivation conditions are ensured via the regular aeration and renewal of the nutrient solution.
Additionally, the use of filled pots ensures a physical stability of the planted systems, which can than sustain a relatively great biomass (cf. Fig. 4). The cultivation duration can be adapted to specific interests such as the influence of the plant development stage (e.g. uptake abilities shortly after germination vs. during flowering).
Fig. 3: Schematic of the Perlite® system
Fig. 4: Example crops grown in Perlite®
Test Design C:
Quartz sand grown plants irrigated with treated solutions
The third higher tier concept protocol consists of plants grown in inert quartz sand and later irrigated with the treated solutions, thus avoiding any disturbance of the roots (cf. Fig. 5). In order to model the ground water situation, the irrigation is given from the bottom of the system, via a peristaltic pump system set with a time schedule.
This additionally ensures minimized surface losses, aerobic conditions and controlled available pore water solution. This system is particularly adapted for the investigation of the plant uptake over a relatively long cultivation period (cf. Fig. 6).
Fig. 5: Schematic of the system
Fig. 6: Example crops grown in quartz sand
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