Influence of Transplanting Practices on Growth and Embolism Levels For Urban Tree Species
Changes in xylem embolism levels due to drought stress or freezing have been documented for a wide variety of plants. High degrees of tissue water stress which lead to increased levels of embolism are also often cited as factors negatively influencing plant establishment. Embolized xylem elements can potentially lead to restriction of stem water flow, thereby reducing growth. Therefore, this dissertation (5 experiments) was undertaken to determine if certain transplanting practices affect embolism dynamics and plant growth of selected urban tree species. Embolism was estimated based on reductions in hydraulic conductance of harvested stem segments. An initial experiment determined the length of time from tissue harvest to embolism measurement that stem samples may be held in cold storage. Results varied between Fraxinus americana L. (white ash) and Acer rubrum L. x saccharinum L. (hybrid red maple), but data suggested white ash stem samples should not be stored more than one day, especially for between-species comparisons. A greenhouse experiment investigated the growth and embolism levels for container-grown Corylus colurna L. (Turkish hazelnut) seedlings in response to root pruning. Increasing levels of root pruning from 25 to 50% increased embolism, although plant height also increased. There was no fertilizer level x root pruning interaction for embolism. A field-harvest and greenhouse growth experiment investigated the influence of cold storage duration on plant growth and pre- and post-transplant embolism levels. Embolism levels increased with duration of cold storage for Acer rubrum L. (red maple), but not for Crataegus phaenopyrum (L.f.) Medic. (Washington hawthorn). After 15 weeks of growth, however, embolism levels were similar for both species. Growth increased with increased cold storage duration for both species. A field experiment investigated the influence of transplant season and root pruning on plant growth and embolism of Turkish hazelnut and Syringa reticulata (Blume) Hara (tree lilac). Embolism levels just prior to budbreak and days to budbreak were highest for fall-transplanted Turkish hazelnut. Embolism level was unaffected by treatments. No clear relationship between embolism and growth could be determined for either species the first season after transplanting. Other fall-transplanted Turkish hazelnuts, however, had growth reductions that corresponded to increasing embolism levels two years after transplanting. An additional transplanting experiment examined the influence of root severance at transplanting on water relations of red maple. Stem sap flow (in vivo) was reduced within 2 h of harvest, and leaf stomatal conductance was reduced 4 h after harvest. Percent embolism (in vitro) was increased within 24 hr of harvest. Results of these experiments indicate that root pruning, and choice of transplant season can reduce plant growth and increase embolism levels. No clear relationship between embolism and growth reduction was evident. Although embolism dynamics are clearly impacted by transplanting, the implications for transplant success are inconclusive. The role of embolism in transplant success was not clear.