Growth, gas exchange, and root respiration of Quercus rubra seedlings exposed to low root zone temperatures in solution culture

Spring planting is standard operational practice in the Central Hardwood Region, though little is known about potential impacts of low root temperature (RT) common during spring on establishment success of temperate deciduous forest tree species. The effects of low RT on growth, gas exchange, and root respiration following winter dormancy were studied in 1-year-old northern red oak (Quercus rubra L.) container seedlings grown in solution culture at uniform air temperatures, but exposed to three different root zone temperatures (10, 15, and 25 °C). After 14 days of treatment, net photosynthesis (A), stomatal conductance (gs), and transpiration (E) were significantly affected by RT; however, these treatment effects did not persist for the remaining measurement period (days 21 and 28) despite growth reductions. After 28 days, new shoot length, leaf area, and number of new roots were reduced with decreasing RT. Shoot dry mass was higher in seedlings exposed to 25 °C compared with those in 10 °C, while an opposite trend occurred for root-to-shoot ratio. Leaf water potential (ψw) at day 28 and days to budbreak were not significantly altered by RT treatments. Root O2 uptake in seedlings exposed to 10 °C was 65% lower than for those seedlings at 25 °C. Low RT has a physiological role in the control of root growth and root respiration, which could potentially affect establishment success of northern red oak seedlings planted in spring when soil temperatures are still low.