RELATIVE PERFORMANCE OF CONIFER POPULATIONS IN VARIOUS TESTS FOR SENSTIVITY TO SO₂, AND THE IMPLICATIONS FOR SELECTING TREES FOR PLANTING IN POLLUTED AREAS

Abstract

SUMMARY The sensitivity of five Pinus and three Picea populations to SO 2 was compared in various types of fumigation experiment (i) > 9 months at 200 μg m −3 , (ii) 6 h at 8000 μ m −3 , (iii) 9 weeks at 800 μg m −3 , (iv) 12 h (overnight) at 17 000 μg m −3 preceded by either 42 days or 6 h at 800 μg m −3 . To complement the fumigation experiments the growth of four of the populations was compared at a polluted (London) and a control site (Silwood Park). There was no relationship between the relative sensitivity of the populations to 200 μg m −3 (measured as relative growth rate) and the degree of acute injury at 8000 μg m −3 . In general the populations of Picea were more sensitive to low concentrations of SO 2 but more resistant to acute injury than those of Pinus. At 800 μg m −3 the initial symptoms were of acute injury, but later whole needles died and were shed. Populations prone to the initial injury were not necessarily sensitive to the later type, and vice versa. Leaf fall was accelerated and dry wt gain depressed at the polluted site compared with the control and these effects were much greater in Picea than in Pinus populations. It is concluded that the order of sensitivity obtained in screening experiments depends largely on the conditions used, and that short‐term experiments with high concentrations of SO 2 cannot be used to predict the responses of conifers to low concentrations of SO 2 in the field.