Influence of Growth from on Ecophysiological Responses to Variable Sunlight in Subalpine Plants

摘要: Periods of variable sunlight due to intermittent cloudcover are common in the subalpine zone central Rocky Mountains. To evaluate ecophysiological significance daily variations sunlight, responses net photosynthesis, stomatal con- ductance water vapor, and use efficiency (CO2 uptake per unit H20 lost) were measured 12 species including trees, shrubs, herbs. Measurements made during intervals alternating full sun shade throughout a growth season that included seasonal periods stress. In general, photosynthesis responded rapidly all forms changes clouds, while conductance more slowly or not at all. Large reductions cloud for species, was considerably less responsive woody species. The greatest most (<10 68% reduction levels) occurred herbaceous Carbon gain enhanced because remained relatively high both periods. Water generally lower compared However, plants maintained higher xylem pressure potentials much nearer values greater decrease herbs resulted improved efficiency, although carbon reduced subsequent full-sun period. These apparent strategies non-steady-state response appear opposite generalizations previously vs. under steady-state conditions.