Abstract
Abstract. Stable isotopic analysis of water in plant, soil, and hydrological studies often requires the extraction of water from plant or soil samples. Cryogenic vacuum extraction is one of the most widely used and accurate extraction methods to obtain such water samples. Here, we present a new design of a cryogenic vacuum extraction system with 18 extraction slots and an innovative mechanism to aerate the vacuum system after extraction. This mobile and extendable multi-port extraction system overcomes the bottleneck of time required for capturing unfractionated extracted water samples by providing the possibility to extract a larger number of samples per day simultaneously. The aeration system prevents the loss or mixture of water vapor during defrosting by purging every sample with high-purity nitrogen gas. A set of system functionality tests revealed that the extraction device guarantees stable extraction conditions with no changes in the isotopic composition of the extracted water samples. Surprisingly, extractions of dried and rehydrated soils showed significant differences of the isotopic composition of the added water and the extracts. This observation challenges the assumption that cryogenic extraction systems to fully extract soil water. Furthermore, in a plant water uptake study different results for hydrogen and oxygen isotope data were obtained, raising problems in the definition from which depths plants really take up water. Results query whether the well-established and widely used cryogenic vacuum distillation method can be used in a standard unified method of fixed extraction times as it is often done.
Highlights
During the past decades, stable water isotopes as natural tracers have become a common tool in plant ecological and pedological research
Experiment #1 demonstrated that the water extraction procedure did not lead to significant differences in isotopic signatures between untreated and extracted tap water samples (δ2H: p = 0.32, δ18O: p = 0.52) (Table 2)
Purging with high-purity nitrogen to prevent a possible isotopic exchange of extracted water with air did not result in significant differences in isotopic composition, neither for local tap water (δ2H: p = 0.22, δ18O: p = 0.69) nor for Schwingbach creek water (δ2H: p = 0.48, δ18O: p = 0.13) (Table 2)
Summary
Stable water isotopes as natural tracers have become a common tool in plant ecological and pedological research. In plant ecology stable water isotopes provide a powerful method for determining seasonal changes in plant water uptake (Corbin et al, 2005; Eggemeyer et al, 2009; Butt et al, 2010; Liu et al, 2010), intra- and interspecific resource competition of plants (Williams and Ehleringer, 2000; Yang et al., 2011), partitioning evaporation and transpiration (Wang and Yakir, 2000; Phillips and Gregg, 2003; Rothfuss et al, 2010, 2012), partitioning of water resources between plants (Stratton et al, 2000; Rossatto et al, 2012), and community wateruse patterns or the zones of root activity in soils (Ehleringer and Dawson, 1992; Thorburn and Ehleringer, 1995; Dawson and Pate, 1996; Liu et al, 2011). Orlowski et al.: Validation and application of a cryogenic vacuum extraction system back the origin (i.e. soil depth) of water in non-transpiring plant tissues
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