WWRC 88-31
Microhabitat Comparisons of Transpiration and Photosynthesis in Three Subalpine Conifers
Abstract
Differences in water and photosynthetic relations were compared for three codominant conifers (Engelmann spruce (Picea
engelmanii), subalpine fir (Abies tasiocarpa), and lodgepole pine (Pinus conlorta)) at microhabitats within a subalpine forest
(central Rocky Mountains, U.S.A.) that were considered representative of different successional stages. Diumal measurements
of photosynthesis, leaf conductance, and transpiration were taken at microhabitats considered early-successional (open),
intermediate (forest gap), and late-successional (forest understory) environments to evaluate possible influences of gas-exchange
physiology in observed distributional and successional patterns. Pine had greater water-use efficiency (photosynthesis/transpiration)
in early- versus late-successional environments, primarily as a result of a lower leaf conductance and transpiration. Photosynthetic
performance was similar among all three species at each respective microhabitat and increased as the openness of the microhabitat
increased. Greater water-use efficiency may significantly improve the growth of pine over spruce and fir on more open, drier sites
at lower elevation. Higher transpiration in spruce and fir may limit these species to higher elevation sites, to understory sites at
middle elevations, and to moister open sites at lower elevations (e.g., riparian sites).
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