Field performance potential of interior spruce seedlings: effects of stress treatments and prediction by root growth potential and needle conductance

Abstract

Root growth potential (RGP) and needle conductance to water vapour (Gn) of container-grown interior spruce (Piceaglauca–(Moench) Voss Piceaengelmannii Parry complex) seedlings that had been subjected to mechanical (dropping), low-temperature (−15 °C), or heat (35 °C) stresses were determined prior to planting on two forest sites. Field performance measured as survival, height, stem diameter, stem volume, and mean stem volume relative growth rate (RGR) was assessed for each of the 4 years following planting. RGP, Gn, and field performance did not differ between mechanically stressed and nonstressed seedlings. Low temperature and heat stresses reduced RGP, Gn, and field performance of some batches of seedlings, indicating that stock lots with different nursery cultural history had substantially different stress resistance. RGP and Gn were correlated with field performance such that for RGP greater than five new roots per seedling, high (>80%) survival and to a lesser extent greater growth occurred, whereas for RGP less than five new roots per seedling, survival and growth were unpredictable. High survival and better growth occurred for stock lots having Gn > 50 mmol•m−2•s−1, while for Gn < 50 mmol•m−2•s−1, survival decreased. Preplanting stress effects on growth were small and due to RGR reductions in the first field season, which are projected to result in a time delay of 1 year or less in trees reaching a height of 150 cm and a stem diameter of 3.5 cm.