Root hydraulic conductivity and root growth capacity of black spruce (Picea mariana) seedlings.

The relationship between root elongation and root hydraulic conductivity was investigated in 1-year-old, overwintered black spruce (Picea mariana (Mill.) seedlings. Hydraulic conductivity was estimated by observing water flux through decapitated roots under positive pressure. Five hydraulic conductivity parameters were estimated: (1) water flux under a minimal pressure of 0.2 MPa (J(v, min)); (2) pressure at which a linear relationship between water flux and pressure began (P(min)); (3) slope of the linear water flux-pressure relationship (L(v)); (4) pressure at which the linear relationship between water flux and pressure ended (P(max)); and (5) maximum water flux (J(v, max)). Between day 1 and day 2 after thawing of the growing medium, there were significant increases in L(v) and J(v, max) but there was little, if any, root elongation. Root elongation averaged 5.4 cm seedling(-1) 5 days after thawing and 88.2 cm seedling(-1) 20 days after thawing. Root hydraulic conductivity increased with new root length initially. But between days 20 and 30, when new root length nearly doubled, P(min) was the only measure of hydraulic conductivity that increased significantly. There were significant correlations (P < 0.05) between white root length and both J(v, min) (r(2) = 0.90) and J(v, max) (r(2) = 0.91).