Effect of selection on shoot elongation rhythm of eastern white pine ( Pinus strobus L.) and its implications to seed transfer in Ontario

Abstract

Shoot elongation patterns of eastern white pine ( Pinus strobus L.) from 112 natural populations in Ontario were studied for 2-year-old seedlings in a greenhouse and 7-year-old trees in a field provenance test. Shoot elongation curves were fitted with a logistic function for individual seedlings and trees, from which several shoot elongation rhythm variables were predicted. The effects of within population selection for increased growth on the shoot elongation rhythm variables were investigated at different selection intensities. Results indicate that faster growth in eastern white pine is associated with both an earlier start and later cessation of shoot elongation for individuals and populations. While among population variation is significant, from 83 to 92% of phenotypic variation in estimates of shoot elongation curve parameters and growth rhythm variables resides within populations, which tends to minimize the effects of geographic seed transfer on the synchronization between shoot growth rhythm and local climate. Within population, selections for increased growth can result in substantial change in population statistics of shoot growth rhythm variables. A selection intensity as low as 50% in height growth can delay shoot elongation cessation by nearly 6 days and expand the shoot elongation period by 8 days. The implications of changes in shoot elongation rhythms to seed transfer in Ontario are discussed.