Canadian Forest Service Publications
Gas exchange response of western hemlock seedlings from various dormancy-induction treatments to reforestation site environmental conditions. 1992. Grossnickle, S.; Arnott, J.T. Forest Ecology and Management 49: 177-193.
Issued by: Pacific Forestry Centre
Catalog ID: 3272
Available from the Journal's Web site. †
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Western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings from four dormancy-induction treatments (i.e. long-day dry, long-day wet, short-day dry, short-day wet) had needle conductance (gwv) and net photosynthesis (Pn) patterns monitored over the first field growing season. The objective was to compare stocktype response with environmental conditions on a coastal reforestation site in British Columbia. Both Pn and gwv response to photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) were determined using boundary line analysis. This defined the stocktypes' maximum gas exchange respoonse (i.e. PnMAX. and gwvMAX.) to field site environmental conditions. Short-day wet and long-day dry seedlings had greater PnMAX with increasing PAR after frost. Short-day seedlings had greater PnMAX. with increasing PAR during summer conditions compared with long-day seedlings. The gwvMAX response to PAR was suppressed after frost in all seedlings. Short-day seedlings had greater gwvMAX. response to PAR from March through June. All treatments showed a linear decrease in PnMAX. with increasing VPD, though short-day seedlings had the greatest PnMAX. with increasing VPD. One-year-old needles from seedlings in all treatments had very little change in gwvMAX. with increasing VPD. For current-year needles, all treatments had a decrease in gwvMAX. as VPD increased, though short-day seedlings had the greatest gwvMAX. Both Pn and gwv decreased at lower shoot water potentials in all treatments, but between – 0.5 and –1.0 MPa short-day seedlings had greater Pn and gwv. At gwv measurements greater than 1.0 mm s-1, short-day wet seedlings had the least reduction in non-stomatal Pn limitations implying a greater water-use efficiency.