Growth, morphology, and gas exchange in white spruce (Picea glauca) seedlings acclimated to different humidity conditions

The study examined the effects of different relative humidity conditions at germination, early growth, and following cold storage on morphological and physiological characteristics of white spruce (Picea glauca (Moench) Voss) seedlings. Seedlings that were grown for 18 weeks following seed germination at the lower, 30% RH (RHinitial) treatments were shorter and had smaller stem diameters, shorter needles with more epicuticular wax, and a greater density of needles per centimetre stem, compared with the 80% RHinitial seedlings. After 18 weeks of growth under 30, 50, and 80% RH, the seedlings were hardened off, stored for 8 weeks at 3°C and planted in pots in growth chambers under 42 and 74% relative humidity (RHsubsequent). Under 74% RHsubsequent conditions, the lower RHinitial seedlings flushed sooner and had higher growth rates compared with the higher RHinitial seedlings. When the higher RHinitial seedlings were placed under 42% RHsubsequent conditions, their bud flush was delayed, and subsequent growth rates were lower compared with the lower RHinitial seedlings. When measured at 40% RH, seedlings subjected to lower RHinitial had higher net assimilation rates and stomatal conductance compared with the seedlings acclimated to higher RHinitial humidity. It was concluded that the humidity conditions present during early seedling growth following germination significantly affect their morphological and physiological characteristics during the second growth season.