Premium
LEAF GAS EXCHANGE IN QUERCUS MACROCARPA (FAGACEAE): RAPID STOMATAL RESPONSES TO VARIABILITY IN SUNLIGHT IN A TREE GROWTH FORM
Author(s) -
Knapp Alan K.
Publication year - 1992
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1992.tb14601.x
Subject(s) - deciduous , evergreen , biology , stomatal conductance , botany , photosynthesis , fagaceae , andropogon , horticulture , xylem , shade tolerance , canopy
Responses in net photosynthesis (A), stomatal conductance to water vapor (g), and leaf xylem pressure potential ( ψ ) were measured in the deciduous tree Quercus macrocarpa during alternating periods of sun (photosynthetic photon flux, PPF > 1,500 μ mol m ‐2 sec ‐1 ) and shade (ca. 350 μ mol m ‐2 sec ‐1 simulating cloud cover). Measurements were made on trees growing at the gallery forest‐prairie edge on the Konza Prairie Research Natural Area in northeast Kansas. The region is near the westernmost extension of the range of Q. macrocarpa where this species experiences significant seasonal water stress (minimum ψ < ‐2.9 MPa). Quercus macrocarpa was chosen for study because it has relatively high A (15 μ mol m ‐2 sec ‐1 ) and g (300 mmol m ‐2 sec ‐1 ) in contrast to the deciduous and evergreen subalpine trees previously studied. Both trees and large saplings of Q. macrocarpa responded to alternating several minute periods of sun and shade with relatively rapid changes in A and g. Reductions in g (110 mmol m ‐2 sec ‐1 ) during shade periods lowered transpirational water losses (E) by 13% (and reduced A by 5%) relative to estimates of A and E made assuming g remained constant. Partial stomatal closure during shade was correlated with moderate enhancement in ψ (0.31 MPa) in Q. macrocarpa . However, greater increases in ψ were measured in adjacent prairie grasses exposed to similar periods of shade (0.72 MPa in Andropogon gerardii , 0.61 MPa in Sorghastrum nutans ). Reduced variability in ψ in tree growth forms may reflect greater buffering of water relations associated with the large size of trees, the amount of tissue devoted to water storage, and differences in hydraulic resistance relative to herbs. Nonetheless, the gas exchange and water relations responses in Q. macrocarpa were much more similar to those previously measured in herbaceous subalpine and grassland species than to those documented for subalpine trees. Thus, rapid gas exchange responses to variable PPF may also occur in tree growth forms.