荒漠植物蒙古扁桃水分生理特征

 蒙古扁桃（Prunus mongolica）是荒漠区和荒漠草原的水土保持植物和景观植物，是蒙古高原古老残遗植物，对其深入研究对于了解蒙古高原植被演替以及对当地生态环境的稳定和恢复有着重要意义。该实验采用PV技术和自然脱水法探讨了蒙古扁桃的水分生理特性。结果表明：在自然状态下，蒙古扁桃幼苗叶片的相对含水量为69%，饱和含水量为117%，临界饱和亏为48%，水势为-0.85 MPa。经 5% PEG-Hoagland (-0.46 MPa)干旱胁迫处理3 d后，其相对含水量、临界含水量和水势分别下降到48%、39%和 -1.97 MPa，而饱和含水量和束缚水与自由水比值分别增加到187%和11.94。对失水率分析的结果表明：在正常水分状态下，蒙古扁桃幼苗经102 h自然脱水后失水达到平衡，而经过干旱胁迫处理3 d后，其失水率曲线斜率变小，失水过程明显减缓，失水最终达到平衡的时间延长到152 h，其保水能力显著提高。将旱生植物蒙古扁桃的失水率曲线与中旱生植物长柄扁桃（P. pedunculata） 的失水率曲线相比较发现，蒙古扁桃的耐脱水能力明显强于中旱生植物长柄扁桃。PV曲线(Pressure-volume curve)分析结果表明:蒙古扁桃饱和含水量渗透势（Ψπ¹⁰⁰）和零膨压渗透势 （Ψπ⁰）很低，分别为-2.49 MPa和-3.11 MPa，而Ψπ¹⁰⁰和Ψπ⁰差值较大（0.62 MPa）,表明其维持膨压的能力很强。其细胞壁弹性模量值低(4.18 MPa)进一步表明，蒙古扁桃具有很强的膨压调节能力。蒙古扁桃幼苗失去膨压时的渗透含水量（ROWC^tlp）为80%，这是其细胞壁特性所决定的渗透调节能力的基础。蒙古扁桃质外体含水量（AWC, %）较高（79%），因而具有较高的束缚水与自由水比值（7.76），这是其耐脱水性的生理基础。总之，蒙古扁桃叶水势、渗透势低有利于其根部对深层土壤水分的吸收，而较高的束缚水与自由水比值及较低的细胞壁弹性模量是其耐脱水的生理基础。

HYDROLOGICAL CHARACTERISTIC OF THE DESERT PLANT PRUNUS MONGOLICA ON THE MONGOLIANPLATEAU OF CHINA

Aims Prunus mongolica is a xeric shrub, a landscape plant, a water and soil conservation plant, and an ancient species in the desert and desert steppe of the Mongolian Plateau, China. It tolerates extreme aridity and poor soil, growing strongly in desert where annual rainfall is <200 mm and annual evaporation is 3 400-4 000 mm. Study of P. mongolica is useful for understanding plant succession on the Mongolian Plateau and for sustaining and restoring the local ecosystem.  Methods The Abbe refractometer method, the natural dehydration method and the PV technique were used to analyze the hydrological characteristic of P. mongolica. Important findings The relative water content, saturation water content, critical saturation deficit and water potential of P. mongolica seedling leaves were 6 9%, 117%, 48% and -0.85 MPa, respectively. The relative water content, critical water content and leaf water potential of P. mongolica seedlings exposed to drought stress decreased to 48%, 39% and -1.97 MPa, respectively, but the saturation water content and the ratio of bound water/free water increased to 187% and 11.94, respectively. The natural dehydration experiment indicated that P. mongolica seedlings reached equilibrium after 102 h in normal condition, but the dehydration rate decreased and the dehydration equilibrium time was delayed after 3 d of drought stress. This proved that the water-holding ability of P. mongolica increased after drought stress. In comparing the dehydration rates of the xerophytic P. mongolica and the mesophytic P. pedunculata, we discovered that the dehydration tolerance capacity of P. mongolica was higher than that of P. pedunculata. Analysis of PV curve showed that osmotic potential (Ψπ¹⁰⁰) of water saturation and osmotic potential (Ψπ⁰) at turgor loss point of P. mongolica seedling were -2.49 MPa and -3.11 MPa, respectively. The fact that the difference of Ψπ¹⁰⁰ andΨπ⁰ was very large and the values very low showed that P. mongolica had strong ability to regulate turgor pressure. The ratio of bound water/free water was relatively high (7.76), and the modulus elasticity of cell wall was 4.18 MPa. The low leaf water potential and low osmotic potential of P. mongolica were beneficial for absorption of water from soil depths. Our results indicated that P. mongolica was a strong xerophyte in terms of hydrology. Its high ratio of bound water and free water, low osmotic potential at saturation water content, osmotic potential at turgor loss point and low modulus elasticity of cell wall were the physiological fundamentals of its dehydration tolerance.