OPEN-TOP CHAMBER AND FIELD EXPOSURE OF SITKA SPRUCE TO SIMULATED ACIDMIST - A COMPARISON OF RESULTS

Sitka spruce seedlings gl own in pots of compost in open-top chambers (OTCs) or outside, in an agricultural loam soil, in different years, w ere treated with pH 2.5 acid mist comprising an equimolar solution, of H2SO4 and NH4NO3 at 1.6 mol m(-3). The effects of rain, and frequency of acid mist applications on visible injury, nutrition and frost hard iness were evaluated in the OTC experiment. Similar evaluations were u ndertaken in the field where application frequency was dependent on wi nd-speed, rain and direct sunlight. Rain washing significantly amelior ated the effect of acid mist on frost hardiness in OTCs. In the field experiment there was no effect of acid mist treatment. Increasing the frequency of misting in OTCs for the same exposure exacerbated the det rimental effects of acid mist, causing both visible damage and further increasing the sensitivity of the acid treated trees to freezing temp eratures. The results show that the treatment environment can both ame liorate and exacerbate treatment effects. (C) 1998 Elsevier Science Lt d. All rights reserved.