Effects of depth of water table and substrate temperature on root and top growth of Picea mariana and Larix lancina seedlings
Three thermally insulated tanks were divided in half and one side of each was cooled using a network of copper tubing, through which chilled ethylene glycol was pumped. Tanks were filled with peat and seedlings of black spruce (Piceamariana (Mill.) B.S.P.) and tamarack (Larixlaricina (Du Roi) K. Koch.) were transplanted to both ambient and cooled sides. Water table levels of the tanks were maintained at either 4, 10, or 25 cm below the substrate surface. Root biomass, length, and maximum depth, and shoot height, biomass, and branching for both species were lowest in the tank with water table at 4 cm below the surface. Oxygen diffusion rates were lowest and lenticel intumescences of black spruce roots most abundant in this treatment. With water table depth at 25 cm, the cooling treatment (9 °C at the 10 cm level) had a negative effect on root growth compared with the ambient treatment (18 °C at the 10 cm level). The reverse was true for the tank with water levels at 4 cm; the cooled side had greater root growth than the ambient side.