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Root severance during field harvesting alters the water status of a tree, resulting in water stress and reduced post-transplant growth. Two experiments, using Acer rubrum L. (red maple), determined the influence of root severance at harvest on sap flow and xylem embolism. Trees 1.5–1.8 m tall (4 years old) were utilized in the first experiment, and trees 1.2–1.5 m tall (2 years old) were utilized in the second. Sap flow sensors were installed on the 4-year-old trees prior to root severance and remained on the trees until 1 week after harvest. Within 1 day after root severance sap flow was reduced and remained lower than nontransplanted (control) trees for the remainder of the experiment. Leaf stomatal conductance (Cs) of transplanted trees 1 week after root severance was lower than that of control trees, but leaf water potentials (ψ) were similar. In the second experiment, sap flow was reduced relative to control trees within 2 h after root severance. Although Cs was reduced 4 hours after root severance, ψ was not. Embolism increased within 24 hours of root severance. These results indicate that root severance quickly induces increased levels of embolism, which is associated with reduced sap flow.
Fundamental information regarding posttransplant root and shoot growth dynamics is needed to better understand transplant establishment. Seasonal patterns of root, shoot, and trunk growth of balled-and-burlapped and pot-in-pot (PIP) sugar maples (Acer saccharum Marsh.) transplanted at leaf drop (Nov. 2000), late fall (Dec. 2000), early spring (Mar. 2001), budbreak (Apr. 2001), or budset (July 2001) were measured and compared with nontransplanted field- and PIP-grown trees. All trees exhibited a pattern of maximum shoot extension, root growth, and trunk expansion in early May, late May, and early June, respectively. Maximum root growth was concurrent with early trunk expansion, both of which began when shoot growth was decreasing. Root growth was characterized by periods of abundant growth in late May and early June and less growth in summer and early fall. Transplanting at fall leaf drop, in late fall or spring, or at budbreak did not appear to radically disrupt the normal growth periodicity of sugar maple. However, transplanting at budset (summer) resulted in abundant root growth 11 weeks later than the period of maximum root growth in all other treatments. Our data indicate that similar amounts of root regeneration can be expected for irrigated July-transplanted trees as for trees transplanted in fall and spring. As well, our study provides evidence of root mortality during the winter and spring after the first posttransplant growing season. Although minimal root mortality was evident in nontransplanted field trees, substantial root mortality was evident in the nontransplanted PIP trees during winter and early spring.
Root system regeneration after transplanting of large trees is key to successful establishment, yet the influences of different production systems and transplant timing on root growth remain poorly understood. Patterns of new root production and mortality were therefore measured for 1 year after transplanting landscape-sized Acer saccharum Marsh. (sugar maple). Trees were transplanted into root observation chambers (rhizotrons) from two production systems, balled-and-burlapped (B&B) and pot-in-pot (PIP), in November, December, March, April, and July and compared with non-transplanted trees. Although root production stopped in midwinter in all transplants and non-transplanted field-grown trees, slight wintertime root production was observed in non-transplanted PIP trees. Root mortality occurred year-round in all treatments with highest mortality in winter in the transplanted trees and spring and summer in the non-transplanted trees. Non-transplanted PIP trees had significantly greater standing root length, annual production, and mortality than non-transplanted field and transplanted PIP trees. For B&B trees, greatest standing length, production, and mortality occurred in the April transplant treatment. Production and mortality were roughly equal for non-transplanted trees, but production dominated early dynamics of transplanted trees. Overall, increases in root length occurred in all treatments, but the magnitude and timing of root activity were influenced by both production system and timing of transplant.