EFFECTS OF SOIL CHEMISTRY ON THE RESPONSE OF POTTED SITKA SPRUCE TO ACID MIST IN OPEN-TOP CHAMBERS

Bare rooted Sitka spruce seedlings were grown in an agricultural loam, acid brown forest and a peaty forest soil in open-top chambers. Visib le injury (brown lesions and necrosis) was observed after 3 weeks of t reatment with pH 2.5 mist applied 4 times a week in all 3 soil types. The overall N dose, equivalent to 25 kg N ha(-1), stimulated seedling growth in the two acid forest soils but not in the base rich agricultu ral soil. In this soil the effect of the additional N on the available N pool was much smaller than on the more acid soils. Frost hardiness was reduced on all 3 soils. There was no relationship between hardines s (LT(50)) and N availability, foliar N or foliar S concentrations. Th e reduction in frost hardiness and the amount of visible injury was gr eatest on the most acid soil, where soil pH was significantly reduced by acid treatment. Significant effects of soil chemistry on seedling p erformance were also observed in the absence of acid treatment. These results suggest that results of acid mist effects studies based on pla nts grown in compost provide an 'incomplete' potentially misleading pi cture of acid mist effects on trees.