| Growth and water relations of Kentucky coffee tree [Gymnocladus
dioica (L.) K. Koch] whips in translucent tubelike shelters were investigated.
In a container study, 1.2-m-high shelters were placed over whips following
transplanting, then diurnal microclimate, water relations, and water use
were measured. Shelter air temperature and vapor pressure were substantially
higher, and solar radiation was 70% lower, than ambient conditions. Sheltered
trees responded with nearly three-times higher stomatal conductance than
nonsheltered trees. However, due to substantially lower boundary layer conductance
created by the shelter, normalized water use was 40% lower. In a second
experiment, same-sized shelters were placed on whips following spring transplanting
in the field. Predawn and midday leaf water potentials and midday stomatal
conductance (gs) were monitored periodically through the season,
and growth was measured in late summer. Midday gs was also much
higher in field-grown trees with shelters than in those without. Sheltered
trees in the field had four times greater terminal shoot elongation but
40% less stem diameter growth. Attenuated radiation in the shelters and
lower specific leaf area of sheltered trees indicated shade acclimation.
Shelters can improve height and reduce water loss during establishment in
a field nursery, but they do not allow for sufficient trunk growth. |