Abstract
Interior spruce (Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm.) somatic seedlings from a range of clones were measured for gas exchange processes in relation to summer atmospheric parameters. Carbon isotope composition ( delta 13C) of needles was compared with gas exchange parameters and intrinsic water use efficiency (WUEi). Needle conductance (gwv) decreased as vapour pressure deficit (VPD) increased. Clone T703 had the lowest gwv level across all VPD conditions, with clones G351, N366, and W460 having significantly greater gwv than clone T703 at VPD levels <2.0 kPa. Response of net photosynthesis (Pn) to photosynthetically active radiation (PAR) for all clones showed Pn to increase to PAR levels of around 1000 µmol ·m-2 ·s-1 and then, Pn rates were stable at higher PAR levels. Clones N366 and W460 had significantly greater Pn than clone T703 at all PAR levels. All clones showed Pn to decline as VPD increased, with clone W460 having the highest predicted Pn level across all VPD conditions and significantly greater Pn than clone T703. Higher WUEi was related to an increase in delta 13C, with clone T703 having the highest WUEi and delta 13C, followed by clone W460. Changes in delta 13C, for all clones, indicated a stronger relationship with gwv than with Pn.
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