EXPERIMENTAL AND NUMERICAL-ANALYSIS OF STOMATAL ABSORPTION OF SULFUR-DIOXIDE AND TRANSPIRATION BY PINE NEEDLES

We present the experimental results of flow chamber measurements on SO 2 dry deposition, and of separate field measurements on transpiration of Scots pine (Pinus sylvestris L) twigs under typical northerly summe rtime conditions. These results are interpreted by a numerical model, which solves the steady-state diffusion equation for a single stoma ap proximated to have cylindrical symmetry. An analytical method to estim ate the maximal effect of interference (merging concentration fields o f adjacent stomata) between stomatal pores is introduced. As a result, a functional pore radius is found to be of order of 2-3 mum, which is significantly smaller than the maximal anatomical size of stomatal ap erture. This indicates that stomata are capable to transfer vapours to different degrees. If the obtained estimates for needle resistances a re divided by a factor of 4, the leaf area index of local pine canopy, the bulk stomatal resistance for SO2 is of the order of 200-300 s m-1 .