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Interactions between Drought and Elevated CO2 on Osmotic Adjustment and Solute Concentrations of Tree Seedlings
T. J. Tschaplinski, D. B. Stewart and R. J. Norby
The New Phytologist
Vol. 131, No. 2 (Oct., 1995), pp. 169-177
Stable URL: http://www.jstor.org/stable/2558471
Page Count: 9
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Although drought tolerance of tree species is a critical determinant of forest composition, how elevated CO2 affects drought tolerance is uncertain. Interactions between elevated CO2 and drought on osmotic potential and osmotic adjustment of American sycamore (Platanus occidentalis L.), sweetgum (Liquidambar styraciflua L.), and sugar maple (Acer saccharum Marsh.) were investigated using 1-yr-old seedlings, planted in 81 pots and grown in four open-top chambers, containing either ambient air or ambient air enriched with 300 μmol mol-1 CO2. A well-watered treatment with plants watered daily and a droughted treatment in which plants were subjected to a series of drought cycles were included within each chamber. Sugar maple and sweetgum seedlings completed a total of seven drying cycles, whereas sycamore seedlings, because of their greater leaf area and plant size, completed 11 cycles. The mean soil water potential at re-watering for droughted seedlings in ambient CO2 was -0.5, -0.7, and -1.8 MPa for sugar maple, sweetgum and sycamore, respectively, compared with -0.2, -0.7, and -1.2 MPa, respectively, under elevated CO2. By contrast, all well-watered plants were maintained at soil water potential > -0.1 MPa. Drought under ambient CO2 reduced osmotic potential at saturation for leaves of sycamore and sweetgum by 0.30 MPa and 0.61 MPa, respectively, but leaves of sugar maple did not display osmotic adjustment to drought. Elevated CO2 increased osmotic potential at turgor loss for leaves of sugar maple by 0.33 MPa under well-watered conditions, and 0.48 MPa under drought. This response was not evident in the other species and might be related to the rapid growth of sugar maple causing a depletion of solutes. Whereas drought reduced the total solute concentration in roots of sugar maple, primarily the result of a reduction in K, elevated CO2 did not alter the concentration of total solutes in roots of any of the three species. Elevated CO2 has differing effects on drought tolerance among tree species, and thus might alter the competitive relations between species.
The New Phytologist © 1995 New Phytologist Trust