A passive plant uptake of trace elements can optionally be chosen in the model (see switch PassiveUptake). This uptake is calculated for the leaf, stem and roots separately, and is a function of plant water uptake, Wupt (see section Water uptake by roots). Thus, passive trace element uptake from the mineral pool to the leaf, STEMin→TELeafP, is calculated as:
where CTEMin is the concentration of trace elements in the dissolved phase, sPUscale is a scaling parameter determining the efficiency of the uptake, and fPULeaf is an fraction of the total passive uptake allocated to the leaf.
The same equation is used analogously to calculate the passive uptake to stem, STEMin→TEStemP, and roots, STEMin→TERootsP, by exchanging fPULeaf to fPUStem or fPURoot respectively. The root fraction, fPURoot, is calculated by:
The total passive uptake of trace elements, STEMin→TEPlantP, is the sum of the passive uptake to the leaves, stem and roots.