Morse S R, Wayne P, Miao S L, Bazzaz F A
Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
Oecologia. 1993 Oct;95(4):599-602. doi: 10.1007/BF00317447.
The effect of increasing atmospheric CO concentrations 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) or elevated CO (700 μl l), and both mesic and xeric water regimes. Both CO and water treatment had significant effects on osmotic potential at full hydration, apoplasmic fractions, and tissue elastic moduli. Under xeric conditions and ambient CO concentrations, 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 CO, 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 CO enabled the xeric plants to maintain positive turgor pressures at lower water potentials and tissue water contents. Surprisingly, the elevated CO plants 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 CO conditions.
在美国东北部落叶林常见的先锋树种——纸皮桦中，研究了大气中二氧化碳（CO₂）浓度升高对组织水分关系的影响。通过在环境CO₂浓度（350 μl l⁻¹）或升高的CO₂浓度（700 μl l⁻¹）以及中等水分和干旱水分条件下生长的树苗的压力-容积曲线，估算了组织水分关系的组成部分。CO₂和水分处理对完全水合时的渗透势、质外体部分和组织弹性模量均有显著影响。在干旱条件和环境CO₂浓度下，植物在完全水合时渗透势降低0.15 MPa，组织弹性模量增加1.5 MPa。弹性降低可能使植物在含水量稍有变化时就能改善土壤-植物水势梯度，而较低的渗透势则将零膨压损失点移至较低的水势。在升高的CO₂浓度下，干旱条件下的植物渗透势比中等水分条件下的植物低0.2 MPa，完全水合时弹性模量降低。在升高的CO₂浓度下组织弹性的增加使干旱植物能够在较低的水势和组织含水量下维持正膨压。令人惊讶的是，中等水分条件下升高CO₂浓度处理的植物组织弹性最小。我们认为，尽管在升高的CO₂条件下观察到气孔导度较低，但这种低弹性可能使植物能够从土壤到植物产生有利的水势梯度。
