Control of height growth components in seedlings of California red and white fir by seed source and water stress

Abstract

Terminal bud growth in 2nd-year seedlings and subsequent elongation of the overwintering bud in the 3rd year were studied in California red fir (Abiesmagnifica A. Murr.) and two elevational sources of white fir (A. concolor (Gord. and Glend.) Lindl.). During each growing season the seedlings were either watered or left unwatered to provide 2nd and 3rd year treatments of wet–wet, dry–wet, wet–dry, and dry–dry seasons. Harvests were done biweekly during the second growing season and once at the end of the third growing season. Rate and duration of primordium production were negatively related and there were no differences among seed sources for the number of primordia produced in the 2nd year. Watering more than doubled the number of primordia, mainly through increasing the rate of production. Internode number and length were negatively related on a genetic and environmental basis. Changes in internode length tended to compensate for environmentally induced changes in internode number which resulted in a year to year stability in height growth. Height growth was more buffered against changes in internode number in red fir than in white fir. Watering induced a summer shoot in 80% of low-elevation white fir seedlings and 40% of red fir and high-elevation white fir seedlings. Summer shoots doubled the height increment for the current season and increased the number of needle primordia in the winter bud by 26%. The larger buds were the result of a prolonged period of primordium production.