Processes in the Canopy of Trees: Internal and External Turnover of Elements

To estimate intake of air pollutants and nutrients by balancing the elemental turnover in the canopy of tree stands requires knowledge of internal (leaching) and external (atmospheric intake) fluxes. Wash-off experiments with twigs from spruce differently exposed to atmospheric pollution show a large variety in the contribution of interception deposition (aerosols and gases) to total atmospheric input. By using a gas chamber with filtered air, additional information on plant uptake and leaching (beech) could be gained. It can be concluded from these experiments that plant uptake (and thereby leaching) of Pb and Cr can be neglected, whereas plant uptake of Cd and Cu will be very small. As to Mn, Ca and Mg, plant uptake and thereby leaching plays a more important role. This has to be taken into account, when balancing the turnover of metals in the canopy of tree stands.