09 Feb 2023
 | 09 Feb 2023
Status: this preprint is currently under review for the journal HESS.

Does back-flow of leaf water introduce a discrepancy in plant water source tracing through stable isotopes?

Jeroen D. M. Schreel, Kathy Steppe, Adam B. Roddy, and María Poca

Abstract. Plant water source tracing studies often rely on differences in stable isotope composition of different water sources. However, an increasing number of studies has indicated a discrepancy between the isotopic signature of plant xylem water and the water sources assumed to be used by plants. Based on a meta-analysis we have reconfirmed this discrepancy between plant xylem water and groundwater and suggest back-flow of leaf water (BFLW), defined as a combination of (i) the Péclet effect, (ii) foliar water uptake (FWU) and (iii) hydraulic redistribution of leaf water, as a possible explanation for these observations. Using the average 2.21 ‰ 18O enrichment of xylem water compared to groundwater in our meta-analysis, we modelled the potential of BFLW to result in this observed isotopic discrepancy. With a low flow velocity of 0.052 m.h−1 and an effective path length of 2 m, the Péclet effect alone was able to account for the average offset between xylem water and groundwater. When including a realistic fraction of 5–10 % xylem water originating from FWU and tissue dehydration, 60–100 % of the average observed enrichment can be explained. By combining the Péclet effect with FWU and tissue dehydration, some of the more extreme offsets in our meta-analysis can be elucidated. These large effects are more probable during dry conditions when drought stress lowers transpiration rates, leading to a larger Péclet effect, more tissue dehydration, and a potential greater contribution of FWU.

Jeroen D. M. Schreel et al.

Status: open (until 06 Apr 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on hess-2023-13', Carel Windt, 15 Feb 2023 reply
    • AC1: 'Reply on CC1', Jeroen Schreel, 16 Feb 2023 reply
      • CC2: 'Reply on AC1', Carel Windt, 17 Feb 2023 reply

Jeroen D. M. Schreel et al.

Data sets

Isotopic data of xylem water and groundwater, extracted from literature. Jeroen D. M. Schreel, Kathy Steppe, Adam B. Roddy, and María Poca

Jeroen D. M. Schreel et al.


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Short summary
In recent years, multiple studies have reported a discrepancy between the isotopic composition of water in stems and soil. We hypothesize that isotopically enriched water from the canopy is flowing into the stem (“back-flow of leaf water”; BFLW). Using a meta-analysis on the occurrence of aforementioned isotopic discrepancy, we modelled the effects of BFLW. This modeling approach presents compelling evidence that BFLW can significantly influence the isotopic signature of plant xylem water.