Fine Structure of Acid Mist Treated Sitka Spruce Needles: Open-top Chamber and Field Experiments

Abstract

Sitka spruce grafts (clones DF and 141) grown in open-top chambers (OTC) and ‘mature ’, 6 –8m tall Sitka spruce (clone DF) grown in the field were exposed to acid mist containing an equimolar ion mixture of H 2SO 4and NH 4NO 3at pH2.5. Mist was applied 4 times a week (4 ×1mm) in the OTC experiment and twice a week (2 ×2mm) 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 treatment. Acid mist significantly decreased the amount of calcium deposited in the outer epidermal cell walls, the reduction being most pronounced in the OTCs. Ultrastructurally, acid mist caused a significant increase in chloroplast and grana width. Other symptoms associated with acid mist included swelling of chloroplast thylakoids, chloroplast protrusions, cytoplasm vacuolization, increase in large lipid accumulations and sickle-shaped chloroplast thylakoids. In the OTCs, acid mist hastened the acquisition of frost hardening in both clones. In the field, the control trees exhibited more frost injury than the acid mist treated trees suggesting, again, that acid mist had either hastened or enhanced the stage of frost hardiness of treated trees. In general, acid mist induced changes were more pronounced in the OTCs than in the field.