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. Visible injury (brown lesions and necrosis) was observed after 3 weeks of treatment 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 agricultural 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 hardiness (LT₅₀) and N availability, foliar N or foliar S concentrations. The reduction in frost hardiness and the amount of visible injury was greatest on the most acid soil, where soil pH was significantly reduced by acid treatment. Significant effects of soil chemistry on seedling performance were also observed in the absence of acid treatment. These results suggest that results of acid mist effects studies based on plants grown in compost provide an ‘incomplete’ potentially misleading picture of acid mist effects on trees.