A comparison of extraction systems for plant water stable isotope analysis

Millar, Cody; Pratt, Dyan; Schneider, David J.; McDonnell, Jeffrey J.

doi:10.1002/rcm.8136

Cited by 82 publications

(163 citation statements)

References 36 publications

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“…Of particular importance is the adoption of different sampling protocols for xylem water (e.g., samples collected from twigs or from the stem or from wood cores) and soil material (e.g., Goldsmith et al, showed heterogeneity of isotopic signal due to spatial variability of soil water samples) and different water extraction methods both for xylem water and soil water (Table ). Several studies have reported that different water extraction techniques can return different isotopic composition from the same sample (see the comprehensive review by Millar, Pratt, Schneider, & McDonnell, for plant water samples and comments in Penna et al, ), and that even the same technique carried out in different laboratories can have a strong impact in determining the isotopic composition of soil water (Orlowski et al, ). Therefore, uncertainties associated to the different water extraction techniques can possibly impact our findings.…”

Section: Discussionmentioning

confidence: 99%

Depth distribution of soil water sourced by plants at the global scale: A new direct inference approach

et al. 2020

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The depth distribution of soil water contributions to plant water uptake is poorly known. Here we evaluate the main water sources used by plants at the global scale and the effect of climate and plant groups on water uptake variability and depth distribution. The global meta‐analysis is based on isotope data (δ2H and δ18O) extracted from 65 peer‐reviewed papers published between 1990 and 2017. We applied a new direct inference method to quantify the overlap between xylem water and soil water sources used by plants. The median overlap between xylem water and soil water at different depths varied between 28% and 100%, but they were generally >50%. The shallow (0‐10 cm) soil water overlap with xylem water was largest in cold regions (100% ± 0%) and lowest at tropical sites (about 28%). Conversely, the median overlap between xylem water and deep soil water was largest in the arid and the tropical zones (>75%) and much smaller in the temperate and cold zones. Our results suggest that the isotopic composition of xylem water reflects mostly the signature of shallow soil water (<30 cm) in the cold and the temperate zones, whereas in the arid and the tropical zones, plants appear to exploit water in deeper soil layers. Our novel, simple statistically‐based direct inference method performed well in determining these differences in water sources, and can be applied more widely to isotope‐based plant water uptake studies.

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Section: Discussionmentioning

confidence: 99%

Depth distribution of soil water sourced by plants at the global scale: A new direct inference approach

et al. 2020

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“…We agree that concise and systematic sampling is highly needed to test the TWW hypothesis. In addition to potential methodological problems related to water extraction techniques (Orlowski et al, 2016;Millar et al, 2018) to date studies dealing with the TWW hypothesis do not use a concise sampling protocol in terms of how many plant species or how deep the soil profiles are sampled. Moreover, there is also a lack of description regarding the topography of field sites (e.g.…”

Section: Discussionmentioning

confidence: 99%

A pool‐weighted perspective on the two‐water‐worlds hypothesis

et al. 2019

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Summary The ‘two‐water‐worlds’ hypothesis is based on stable isotope differences in stream, soil and xylem waters in dual isotope space. It postulates no connectivity between bound and mobile soil waters, and preferential plant water uptake of bound soil water sources. We tested the pool‐weighted impact of isotopically distinct water pools for hydrological cycling, the influence of species‐specific water use and the degree of ecohydrological separation. We combined stable isotope analysis (δ18O and δ2H) of ecosystem water pools of precipitation, groundwater, soil and xylem water of two distinct species (Quercus suber, Cistus ladanifer) with observations of soil water contents and sap flow. Shallow soil water was evaporatively enriched during dry‐down periods, but enrichment faded strongly with depth and upon precipitation events. Despite clearly distinct water sources and water‐use strategies, both species displayed a highly opportunistic pattern of root water uptake. Here we offer an alternative explanation, showing that the isotopic differences between soil and plant water vs groundwater can be fully explained by spatio‐temporal dynamics. Pool weighting the contribution of evaporatively enriched soil water reveals only minor annual impacts of these sources to ecosystem water cycling (c. 11% of bulk soil water and c. 14% of transpired water).

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“…Systems such as cryogenic vacuum distillation (CVD) that extract up to 99% of a plant's internal liquid content are not only accessing the transpiration stream, but also intra-and intercellular water, organelle-constrained water, and organic compounds. 1,7 The lack of significant difference between the CVD-2 and DVE results did not fit with the authors' working hypothesis explaining the differences in results noted between the other tested approaches. 1 They postulated that variance in the co-extracted organic compound content, and the extraction of uniquely targeted liquid pools by each extraction method, was responsible for the differences in isotopic results.…”

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confidence: 64%

“…believed that these extraction approaches would provide analytes whose δ 2 H and δ 18 O values were similar, but the authors found significant differences in the isotopic composition of the produced analytes. 1 We report a short follow-up experiment to specifically explore systematic differences between one form of cryogenic vacuum distillation (hereafter CVD-2 from Millar et al, 1 based on Koeniger et al 2 ) and direct vapor equilibration (DVE). 3,4 Millar et al 1 found that DVE was the best extraction method for accessing the plant transpiration stream in wheat.…”

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confidence: 99%