HIGH-TEMPERATURE EFFECTS ON APICAL BUD MORPHOLOGY, DARK RESPIRATION, AND FIXED GROWTH OF BLUE SPRUCE

Night temperatures during bud elongation affected the fixed growth of preformed subapical buds of blue spruce (Picea pungens Engelm., 'Fat Albert' and 'Foxtail') but not apical bud growth. Plant volume decreased when nights were > 14-degrees-C, primarily because of reduced growth of each elongating subapical bud and not a decrease in number of growing points. Apical buds produced under a 30-degrees-C day generally were broader and more flat topped, with more open, noncompressed bud scales than those produced under a 26-degrees-C day. Night temperature had a greater effect on apical bud morphology than day temperature. The extent of bud break and growth during year n + 1 was inversely related to night temperature under which bud initiation and development occurred and directly related to the degree of apical bud normality noted during year n. 'Foxtail' had a greater degree of apical bud normality, a higher percentage of bud break, and retained its characteristic growth habit better than 'Fat Albert' following bud formation at high day and night temperatures. 'Foxtail' also had the lowest respiration rate and appeared to minimize detrimental effects of high temperatures through maintenance of a relatively low respiratory Q10 value (increase in respiration rate for each 10-degrees-C increase in temperature) over a wide temperature range.