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Hydrogen isotope fractionation during water uptake by woody xerophytes

机译：木本旱生植物吸水过程中的氢同位素分馏

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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 super(2)H 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 super(2)H = delta super(2)H sub(soil water) - delta super(2)H sub(xylem water)) ranging from 3ppt to 9ppt was observed in 12 species. A significant positive correlation between salinity tolerance and the magnitude of Delta super(2)H was observed. Water in whole stem segments, sapwood, and roots had significantly lower delta super(2)H values relative to soil water in Prosopis velutina Woot., the species expressing the greatest Delta super(2)H 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 super(2)H 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 super(2)H 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.
机译：稳定的同位素测量广泛用于植物与水的关系研究，以研究从整个植物到生态系统规模的生理和水文过程。常规测量氢和氧的稳定同位素，以鉴定植物源水。该应用基于这样的假设，即在被根吸收期间，水中的氧和氢同位素不会发生分馏。然而，在进入根木质部之前，通过盐生植物和干生植物的根吸收的水的大部分横穿了内胚层中的细胞膜。假设通过该共生途径的水通过会导致分馏，从而导致根部木质部水的super（2）H相对于周围土壤介质降低。我们在受控条件下检查了16种木质盐生植物和旱生植物物种，以证明在根-土界面吸收过程中氢同位素分馏的迹象。在12种物种中观察到3ppt至9ppt的同位素分离（δ超级（2）H =δ超级（2）H子（土壤水）-δ超级（2）H子（木质部水））。盐度耐受性和Delta super（2）H的大小之间存在显着正相关。相对于Prosopis velutina Woot。中的土壤水，整个茎节，边材和根中的水具有明显较低的delta super（2）H值，该物种在所检查的16个物种中表现出最大的delta super（2）H值。加压水流过完整的蒿（Artemisia tridentata Nutt）根系。和滨藜（Pursh）Nutt。导致delta super（2）H值随流量增加而减小。 velutina中未观察到这种关系。沸腾产生的过多热量破坏了根细胞的质膜，并没有显着改变表达水的delta super（2）H与流速之间的关系。根据这些结果，在使用稳定同位素方法检查盐生植物和旱生植物中的源水使用时应格外小心。

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