|SREL Reprint #1946|
Photosynthesis and water-use efficiency of two sandhill oaks following additions of water and nutrients
Milda R. Vaitkus and Kenneth W. McLeod
Water and nutrients are considered the primary factors limiting vegetative growth
in many plant communities. We examined the effects of added water and
nutrients on photosynthesis and water use efficiency (WUE) of juveniles of
Quercus hemisphaerica and Quercus laevis growing together in a sandhill
community in South Carolina. Supplemental water and nutrients were added in a
2 x 2 factorial design. Diurnal photosynthesis was determined approximately
biweekly from June to October and integrated long-term WUE was evaluated
using carbon isotope discrimination at the end of this period. Analysis of diurnal
photosynthesis curves indicated no significant differences between species, but
differences within species were significant between day of sampling, time of
measurement, and treatment. Net photosynthesis of Q. hemisphaerica in
watered treatments was significantly greater than photosynthesis in unwatered
treatments, primarily at midday on days with high temperatures following
prolonged drought. Neither nutrients nor water significantly affected the
photosynthesis of Q. laevis, regardless of environmental conditions. Fertilization
was found to differentially affect WUE of Q. hemisphaerica and Q. laevis,
possibly confounding NWE differences between these two species. Because Q.
hemisphaerica is often found in more mesic environments than Q. laevis, and
because it responded to the addition of water with an increase in photosynthesis,
we concluded that in a sandhill community Q. hemisphaerica juveniles are
limited primarily by water rather than by low fertility. Our results indicated that
juveniles of Q. laevis, the community dominant, are not as plastic as Q.
hemisphaerica in their response to fertilizer and water additions.
SREL Reprint #1946
Vaitkus, M.R. and K.W. McLeod. 1995. Photosynthesis and water-use efficiency of two sandhill oaks following additions of water and nutrients. Bulletin of the Torrey Botanical Club 122:30-39.