title: Elevated CO2and drought alter tissue water relations of birch (Betula populifolia Marsh.) seedlings.
abstract: The effect of increasing atmospheric CO2concentrations on tissue water relations was examined in Betula populifolia, a common pioneer tree species of the northeastern U.S. deciduous forests. Components of tissue water relations were estimated from pressure volume curves of tree seedlings grown in either ambient (350 μl l-1) or elevated CO2(700 μl l-1), and both mesic and xeric water regimes. Both CO2and water treatment had significant effects on osmotic potential at full hydration, apoplasmic fractions, and tissue elastic moduli. Under xeric conditions and ambient CO2concentrations, plants showed a decrease in osmotic potentials of 0.15 MPa and an increase in tissue elastic moduli at full hydration of 1.5 MPa. The decrease in elasticity may enable plants to improve the soil-plant water potential gradient given a small change in water content, while lower osmotic potentials shift the zero turgor loss point to lower water potentials. Under elevated CO2, plants in xeric conditions had osmotic potentials 0.2 MPa lower than mesic plants and decreased elastic moduli at full hydration. The increase in tissue elasticity at elevated CO2enabled the xeric plants to maintain positive turgor pressures at lower water potentials and tissue water contents. Surprisingly, the elevated CO2plants under mesic conditions had the most inelastic tissues. We propose that this inelasticity may enable plants to generate a favorable water potential gradient from the soil to the plant despite the low stomatal conductances observed under elevated CO2conditions.
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Morse
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Wayne
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Miao
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
authors.forename: F A
authors.initials: FA
authors.lastname: Bazzaz
keywords: Cell wall elasticity; Forest regeneration; Global Change; Osmotic adjustment