| No studies have investigated the effect of drought on 1st-year seedling physiology throughout the
first growing season. Germinated seedlings of two pines found at the lower treeline were exposed to a 12 week drought, until mortality was reached. Mortality in Pinus contorta was persistent throughout the drought, while Pinus ponderosa had no mortality until the 12th week, experiencing 100% mortality over a few days. P. ponderosa decreased photosynthesis a week into the drought treatment, while P. contorta maintained photosynthesis for several weeks. P. ponderosa had a greater initial relative growth rate. This spurt of growth lead to increased gas exchange in the cotyledonous stage, which allowed P. ponderosa to maintain a positive carbon balance 11 weeks into the drought. Comparatively, P. contorta maintained a positive carbon balance for only 9 weeks, even though gas exchange persisted during the drought, leaving it vulnerable to both depleted carbon reserves and hydraulic dysfunction.
Keywords: carbon balance, hydraulics, gas exchange, allometry |