Canadian Forest Service Publications
Influence of dormancy induction treatments on the photosynthetic response of field planted western hemlock seedlings. 1994. Major, J.E.; Grossnickle, S.C.; Arnott, J.T. Forest Ecology and Management 63: 235-246.
Issued by: Pacific Forestry Centre
Catalog ID: 3423
Nursery cultural treatments can improve field performance by pre-acclimatizing seedlings to field site conditions. Four dormancy induction treatments (DIT) (i.e. long-day wet, long-day dry, short-day wet, and short-day dry) were examined for their influence on net photosynthesis (Pn) of western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings. Seedlings were planted on a control site with high soil water potential, adequate nitrogen levels and no plant competition. Net photosynthesis was measured in response to a full range of photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) conditions on 1-year-old and current-year needles. The response of Pn to both PAR and VPD was defined by response surface models used to forecast field performance over the range of anticipated environmental conditions.
All models had greater Pn values as PAR increased, but increased VPD resulted in a suppression of Pn. For 1-year-old needles, short-day compared with long-day seedlings, had greater or equivalent Pn response over the range of measured PAR and VPD conditions. For current-year needles, short-day treated seedlings had greater Pn response at high VPD (e.g. 3.8 kPa). Current-year, compared with 1-year-old needles had from 45 to 110% greater Pn over a wide range of PAR (0.5-2.2 mmol m-2 s-1) and VPD (0.5-2.4 kPa) conditions. The results were compared with the testing of these DIT on a reforestation site to determine the validity of measuring physiological responses on a control site as a method for improving nursery cultural treatment selections.