Interior spruce seedlings compared with emblings produced from somatic embryogenesis. III. Physiological response and morphological development on a reforestation site

Interior spruce (Piceaglauca (Moench) Voss × Piceaengelmannii Parry) seedlings and emblings produced through somatic embryogenesis tissue culture were planted on a reforestation site in the central interior of British Columbia. Gas exchange and water relations patterns were monitored over the first growing season and morphological development was monitored over two growing seasons. During shoot elongation, osmotic potential at saturation (Ψ sat ) and turgor loss point (Ψ tlp ) of seedlings and emblings increased, while their maximum bulk modulus of elasticity (ε max ) and total turgor (Ψ ptotal ) decreased, resulting in utilized turgor (Ψ putil ) exceeding 100%. From bud set in late July through October 8, Ψ sat and Ψ tlp decreased, Ψ max and ε Ptotal increased, with Ψ putil between 55 and 70% for both seedlings and emblings. There were few seasonal differences in shoot water relations parameters of seedlings and emblings. One-year-old and current-year needle conductance (g wv ) decreased as vapour pressure deficit (VPD) increased in a similar manner for both seedlings and emblings. Response surface models for net photosynthesis (P n ) of current-year needles showed P n to increase as photosynthetically active radiation (PAR) increased to around 1000 μmol•m −2 •s −1 , and thereafter remained stable, but as VPD increased P n decreased at all PAR levels. Emblings, compared with seedlings, had 15% greater P n under optimal field site atmospheric conditions (i.e., VPD <3.0 kPa and PAR >1000 μmol•m −2 •s −1 ). There was a linear increase in P n as g wv increased in both seedlings and emblings, though 1-year-old needles had higher P n for a given level of g wv than current-year needles. Height and diameter growth across the first and second growing seasons were similar for seedlings and emblings. Seedlings and emblings had similar total root weight after two growing seasons. After the first winter on the field site, survival was 87% for seedlings and 91% for emblings, while emblings had a lower proportion of their foliage damaged by winter conditions. Results indicate that seedlings and emblings were largely comparable in their field performance over two growing seasons on a reforestation site.