Abstract
Periods of variable sunlight due to intermittent cloudcover are common in the subalpine zone of the central Rocky Mountains. To evaluate the ecophysiological significance of daily variations in sunlight, responses in net photosynthesis, stomatal conductance to water vapor, and water use efficiency (CO 2 uptake per unit H 2 O lost) were measured in 12 subalpine species including trees, shrubs, and herbs. Measurements were made during intervals of alternating full sun and shade throughout a growth season that included daily and seasonal periods of water stress. In general, photosynthesis responded rapidly in all growth forms to changes in sunlight due to clouds, while stomatal conductance responded more slowly or not at all. Large reductions in photosynthesis were measured during clouds periods for all species, while stomatal conductance was considerably less responsive to changes in sunlight in woody species. The greatest and most variable reductions in stomatal conductance during shade (<10 to a 68% reduction of full sun levels) occurred in herbaceous species. Carbon gain in the woody species was enhanced because stomatal conductance remained relatively high during both sun and shade periods. Water use efficiency in most species was generally lower during shade periods compared to full sun periods. However, woody plants maintained higher xylem pressure potentials that were much nearer shade values compared to herbs. The greater decrease in stomatal conductance and photosynthesis in herbs during shade resulted in improved water use efficiency, although carbon gain was reduced during both shade and the subsequent full—sun period. These apparent growth strategies during non—steady—state response periods appear opposite to generalizations made previously for woody vs. herbaceous species under steady—state conditions.
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Claims 10
Claim · model-written summary
Photosynthesis of subalpine plants responded rapidly in all growth forms to changes in sunlight due to clouds.
Verbatim
t0“Subalpine Plants”
e0“photosynthesis responded rapidly in all growth forms to changes in sunlight due to clouds”
Claim · model-written summary
Stomatal conductance of subalpine plants responded more slowly or not at all to changes in sunlight due to clouds.
Verbatim
t0“Subalpine Plants”
e0“stomatal conductance responded more slowly or not at all”
Claim · model-written summary
Large reductions in photosynthesis were measured during cloud periods for all species.
Verbatim
t0“Subalpine Plants”
e0“Large reductions in photosynthesis were measured during clouds periods for all species”
Claim · model-written summary
Stomatal conductance was considerably less responsive to changes in sunlight in woody species.
Verbatim
e0“stomatal conductance was considerably less responsive to changes in sunlight in woody species”
Claim · model-written summary
The greatest and most variable reductions in stomatal conductance during shade (<10 to a 68% reduction of full sun levels) occurred in herbaceous species.
Verbatim
e0“The greatest and most variable reductions in stomatal conductance during shade (<10 to a 68% reduction of full sun levels) occurred in herbaceous species”
Claim · model-written summary
Carbon gain in the woody species was enhanced because stomatal conductance remained relatively high during both sun and shade periods.
Verbatim
e0“Carbon gain in the woody species was enhanced because stomatal conductance remained relatively high during both sun and shade periods”
Claim · model-written summary
Water use efficiency in most subalpine species was generally lower during shade periods than during full sun periods.
Verbatim
t0“Subalpine Plants”
e0“Water use efficiency in most species was generally lower during shade periods compared to full sun periods”
Claim · model-written summary
Woody plants maintained higher xylem pressure potentials, much nearer shade values, than herbs.
Verbatim
e0“woody plants maintained higher xylem pressure potentials that were much nearer shade values compared to herbs”
Claim · model-written summary
The greater decrease in stomatal conductance and photosynthesis in herbs during shade resulted in improved water use efficiency.
Verbatim
e0“The greater decrease in stomatal conductance and photosynthesis in herbs during shade resulted in improved water use efficiency”
Claim · model-written summary
Carbon gain in herbs was reduced during both shade and the subsequent full-sun period.
Verbatim
e0“herbs during shade resulted in improved water use efficiency, although carbon gain was reduced during both shade and the subsequent”