Influence of Transplanting Practices on Growth and Embolism Levels For urban Tree Species

Abstract

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.