Foliage dark respiration in Abies amabilis (Dougl.) Forbes: variation within the canopy.

Dark respiration of foliage was measured in a 30-year-old stand of Abies amabilis in western Washington from June to November. Both laboratory and field measurements were used to study the effect of environmental and tree variables on respiration. Foliage respiration rates were most strongly influenced by needle temperature. After accounting for leaf temperature differences, foliage respiration decreased with depth in the canopy for all age classes of foliage. Respiration differences attributed to location within the canopy were greatest early in the growing season, but were still significant in November. Younger foliage respired more than older foliage in the upper canopy, but not in the lower canopy. Respiration differences due to foliage age were highly significant in the early growing season, but were not detectable by mid-October.