FINE-STRUCTURE OF ACID MIST TREATED SITKA SPRUCE NEEDLES - OPEN-TOP CHAMBER AND FIELD EXPERIMENTS

Sitka spruce grafts (clones DF and 141) grown in open-top chambers (OT C) and 'mature', 6-8 m tall Sitka spruce (clone DF) grown in the field were exposed to acid mist containing an equimolar ion mixture of H2SO 4 and NH4NO3 at pH 2.5. Mist was applied 4 times a week (4 x 1 mm) in the OTC experiment and twice a week (2 x 2 mm) on average in the field experiment, between May and Oct, 1991. Samples for light and electron microscopy were collected in Nov. and Jan. following acid mist treatm ent. Acid mist significantly decreased the amount of calcium deposited in the outer epidermal cell walls, the reduction being most pronounce d in the OTCs. Ultrastructurally, acid mist caused a significant incre ase in chloroplast and grana width. Other symptoms associated with aci d mist included swelling of chloroplast thylakoids, chloroplast protru sions, cytoplasm vacuolization, increase in large lipid accumulations and sickle-shaped chloroplast thylakoids. In the OTCs, acid mist haste ned the acquisition of frost hardening in both clones. In the field, t he control trees exhibited more frost injury than the acid mist treate d trees suggesting, again, that acid mist had either hastened or enhan ced the stage of frost hardiness of treated trees. In general, acid mi st induced changes were more pronounced in the OTCs than in the field. (C) 1996 Annals of Botany Company