Hydrogen isotope fractionation during water uptake by woody xerophytes
Hydrogen isotope fractionation during water uptake by woody xerophytes
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DOI：
10.1007/s11104-006-9177-1
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发表时间：
2007-02-01
期刊：
影响因子：
4.9
通讯作者：
Williams, David G.
中科院分区：
文献类型：
--
作者：
Ellsworth, Patrick Z.;Williams, David G.
稳定性同位素测量广泛应用于植物-水关系研究，从植物整体到生态系统尺度研究植物的生理和水文过程。氢和氧的稳定同位素被常规地测量以识别植物源水。这种应用依赖于这样的假设，即在根系吸收过程中，水中的氧和氢同位素没有发生分馏。然而，在盐生和旱生植物中，通过根吸收的大部分水在进入根木质部之前穿过内皮层中的细胞膜。通过这一共质体途径的水已被假设，以引起分馏导致H-2的根木质部水相对于周围的土壤介质中的减少。我们研究了16个木本盐生和旱生植物物种在控制条件下的证据，氢同位素分馏过程中吸收在根-土界面。12种植物的同位素分离度（Δ H-2 = Δ H-2（土壤水）-Δ H-2（木质部水））为3 ~ 9度。Δ H-2的大小与耐盐性呈显著正相关。绒毛牧豆全茎段、边材和根系中的水分相对于土壤水分具有显著较低的Δ H-2值，在16个物种中，表达最大Δ H-2值的物种。加压水流通过三齿蒿完整根系。和四翅滨藜Atriplex canescens（Pursh）Nutt.导致Δ H-2值随流速增加而降低。这种关系在绒毛青霉中没有观察到。通过煮沸产生的过热破坏根细胞的质膜并没有显著改变表达水的Δ H-2与流速之间的关系。鉴于这些结果，在使用稳定同位素方法检查盐生植物和旱生植物物种的源水利用时应注意。
Stable isotope measurements are employed extensively in plant-water relations research to investigate physiological and hydrological processes from whole plant to ecosystem scales. Stable isotopes of hydrogen and oxygen are routinely measured to identify plant source water. This application relies on the assumption that no fractionation of oxygen and hydrogen isotopes in water occurs during uptake by roots. However, a large fraction of the water taken up through roots in halophytic and xerophytic plants transverses cell membranes in the endodermis before entering the root xylem. Passage of water through this symplastic pathway has been hypothesized to cause fractionation leading to a decrease in H-2 of root xylem water relative to that in the surrounding soil medium. We examined 16 woody halophytic and xerophytic plant species in controlled conditions for evidence of hydrogen isotope fractionation during uptake at the root-soil interface. Isotopic separation (Delta H-2 = delta H-2(soil water) - delta H-2(xylem water)) ranging from 3 degrees to 9 degrees was observed in 12 species. A significant positive correlation between salinity tolerance and the magnitude of Delta H-2 was observed. Water in whole stem segments, sapwood, and roots had significantly lower delta H-2 values relative to soil water in Prosopis velutina Woot., the species expressing the greatest Delta H-2 values among the 16 species examined. Pressurized water flow through intact root systems of Artemisia tridentata Nutt. and Atriplex canescens (Pursh) Nutt. caused the delta H-2 values to decrease as flow rate increased. This relationship was not observed in P. velutina. Destroying the plasma membranes of root cells by excessive heat from boiling did not significantly alter the relationship between delta H-2 of expressed water and flow rate. In light of these results, care should be taken when using the stable isotope method to examine source-water use in halophytic and xerophytic species.