Seasonal growth patterns of ovulate strobili of Pinus resinosa in central Wisconsin

Abstract

Seasonal growth patterns and water balance of first- and second-year strobili and seeds of Pinus resinosa Ait. were studied. Strobili emerged from the bud in late May or early June and grew slowly during the first season, reaching approximately 1/40 the weight of mature strobili. After a rapid period of hydration which lasted until mid-June, the weight of water in first-year strobili remained stable, but percentage of moisture decreased, primarily because of increasing dry weight. Strobili resumed growth in mid-April of the second year and grew slowly until June. Then, at about the time that fertilization of ovules occurred, dry weight increment of strobili increased greatly until a final weight of 6 to 8 g was reached early in August. However, strobili reached final size in mid-July. After mid-June, both the weight of water and percentage of moisture of second-year strobili decreased greatly, reflecting characteristic dehydration of cones during maturation. Seeds increased rapidly in dry weight after fertilization, but decreased sharply in percentage of moisture and weight of water.Continuous monitoring of strobilus diameters with dendrographs showed that, during the first year, strobili expanded slowly and showed diurnal fluctuations in diameter during periods of water stress. Second-year strobili showed three growth phases: an initial phase characterized by net diameter increment; a second phase in which no large net diameter increment took place although diurnal fluctuations regularly occurred; and a third, dehydration, phase during which time strobilus diameters decreased, accompanied by diurnal contraction and partial reexpansion.