Modelling solute uptake and incorporation into vegetation and litter

The concepts and algorithms of the Baldwin, Nye and Tinker model describing solute movement from bulk soil solution to roots (DIFMAS) and a model of solute dynamics and accumulation in plant tissues and litter (DRYADS) are presented. Foliar uptake of solutes and gases are included in the DRYADS code. These models form components in a coupled system of models having hourly resolution of carbon, water, and solute dynamics in terrestrial ecosystems. Applications showing successive hourly, monthly, and annual results illustrate the utility of the models. The DRYADS model sensitivity to both leaf solute conductivity and root solute conductivity parameters suggest the importance of careful experimental determination of these plant properties. The tissues of solute entry (leaves, roots) initially accumulate solutes in a fixed form in preference to the more remote tissues (stems, fruits). Model application results show that root sapwood is the first major site of trace contaminant accumulation from soil-borne pollutants. The algorithms describing solute movement along a concentration gradient in phloem and as mass flow in the xylem transpiration stream result in high mobility of solutes in vegetation. The simulated diurnal pattern of root solute uptake showed that more than 85% of solutes were taken up during the daylight hours. The simulations further showed that contaminants had the greatest effect on the litter system. Toxic effects of contaminants on decomposition resulted in lower mineralization losses and accumulation of contaminant in litter with continuing deposition.