Transplanted red oak seedlings mediate transplant shock by reducing leaf surface area and altering carbon allocation

Abstract

One-year-old red oak seedlings (Quercusrubra L.) from three open-pollinated families were produced in 1 m tall containers during 1989. In spring 1990, the seedlings were either transplanted (which included pruning the main root to a 15-cm length) or not. Transplanted seedlings either received a 5-s basal dip in 20 mM indole-3-butyric acid or did not. The seedlings were placed in a greenhouse and harvested at the beginning of the first lag phase, at the beginning of elongation of the second growth flush, and 70 days after the beginning of the experiment. Root-pruning removed 42 to 50% of whole-plant dry weight. Transplanted seedlings had significantly reduced leaf surface area and began a second growth flush later than untransplanted seedlings. There were no treatment differences in CO2 assimilation rate on a per unit leaf surface area. Predawn xylem water potential in transplanted seedlings was lower than in untransplanted seedlings. Transplanted seedlings used less root and more shoot reserves to develop the first flush than untransplanted seedlings. Treating root-pruned seedlings with 20 mM indole-3-butyric acid did not significantly increase growth potential compared with untreated transplanted seedlings. For transplanted red oak, transplant shock seems to be mediated through reduced leaf surface area, which reduces whole-plant water use.

Drought susceptibility and recovery of transplanted Quercus rubra seedlings in relation to root system morphology

“…Transplant shock was also indicated by reduced leaf area (Fig. 4B) consistent with results for loblolly pine (Pinus taeda L.) (Teskey et al, 1987), Douglas-fir (Haase and Rose, 1993), and northern red oak (Struve and Joly, 1992) seedlings. The mild water stress in WW plants following transplant indicates that there is a time lag during which transplanted seedlings must re-establish rootsoil contact for resource exploitation, and may also infer temporary impairment of root function (Burdett, 1990;Sands, 1984).…”

“…In addition, reduced leaf area as observed in smaller RvC seedlings (Fig. 4) is yet another drought avoidance mechanism that alleviates transplant shock under high moisture stress (Struve and Joly, 1992). Hence, smaller transpiring leaf area as observed in RvC1 seedlings may increase survival and growth potential on droughty sites.…”

“…Most artificial forest regeneration projects involving northern red oak use 1 + 0 or 2 + 0 bareroot seedlings for field planting (Jacobs et al, 2004b). These seedlings undergo significant transplant shock following planting, which may be associated with loss of fine root structure during nursery lifting (Struve, 1990;Struve and Joly, 1992).…”

“…Seedling physiological responses, such as reduced A, transpiration (E), stomatal conductance (g s ), and leaf xylem water potential (Ψ L ) implicate planting shock (Blake, 1983;Grossnickle, 1988). Plant morphological indicators of planting shock include reduced leaf area, restricted shoot growth, shortened needles, and a greater number of needles per unit of leader (Haase and Rose, 1993;Struve and Joly, 1992).…”

“…However, large Rv is often correlated with large shoots, and the transpirational demand after budbreak coupled with insufficient water uptake may result in higher water deficits (Sands, 1984), which could induce transplant shock detrimental to field performance of seedlings. Consequently, seedling field survival and growth may depend on ability to mitigate internal water deficits and/or resist drought (Grossnickle, 2005;Struve and Joly, 1992), especially for northern red oak, which is generally restricted to relatively mesic sites (Sander, 1990).…”