Tree water deficit and dynamic source water partitioning

Nehemy, Magali F.; Benettin, Paolo; Asadollahi, Mitra; Pratt, Dyan; Rinaldo, Andrea; McDonnell, Jeffrey J.

doi:10.1002/hyp.14004

Cited by 46 publications

(80 citation statements)

References 137 publications

(249 reference statements)

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“…The prolonged transpiration breakthrough suggests that there was no characteristic uptake depth and that the plant, on average, used water from all depths. The tracer breakthrough (Figure 6a) also had irregular fluctuations that likely reflected some progressive shift toward shallower/deeper sources depending on tree water status as outlined in Nehemy et al (2021). This behavior is consistent with the observed root architecture: fine roots (<2 mm) were observed throughout the entire soil column, up to 2 m depth (Nehemy et al, 2021).…”

Section: The Age Of the Transpiration Fluxsupporting

confidence: 77%

“…The tracer breakthrough (Figure 6a) also had irregular fluctuations that likely reflected some progressive shift toward shallower/deeper sources depending on tree water status as outlined in Nehemy et al (2021). This behavior is consistent with the observed root architecture: fine roots (<2 mm) were observed throughout the entire soil column, up to 2 m depth (Nehemy et al, 2021). The relative uniform and deep presence of fine roots suggests that water uptake was not constrained to any depth or sector.…”

Section: The Age Of the Transpiration Fluxsupporting

confidence: 72%

“…Red color denotes water compartments that were sampled for isotopic analyses. details of this experiment concerning the tree water deficit dynamics and the isotope composition of leaf water are described by Nehemy et al (2021) and Benettin et al (2021).…”

Section: Experimental Designmentioning

confidence: 99%

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Tracing and Closing the Water Balance in a Vegetated Lysimeter

Benettin

Nehemy

Asadollahi

et al. 2021

Water Resources Research

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The water balance is ecohydrology's most important equation. Rodriguez-Iturbe (2000) notes that although apparently simple, it still presents serious challenges when infiltration, evapotranspiration, and leakage are all dependent on soil moisture dynamics. While useful, the black box water accounting model is unable to mechanistically assess mixing dynamics, ages of the water fluxes, and partitioning dynamics. Because of this, there have been recent calls for a different way of addressing the water balance (McDonnell, 2017)-one that tracks both the input-storage-output relations and the age of each component. This is because closure of the water balance (annually, the tradition in catchment hydrology) is physically unrealistic when individual water balance components can greatly exceed 1 year. Indeed, traditional hydrometric approaches to water balance closure only describe how much water flows through a system and not which water.In a recent review, Sprenger et al. (2019) noted that empirical water age data in the critical zone remains scarce and "with improving technology, we are gaining insights into the diversity of water ages within pools that have been elsewhere treated as well-mixed buckets." Some examples include the fact that two third of groundwater below 250 m is more than 10,000 years old (Jasechko et al., 2017); that often summer transpiration can be older water from previous seasons (Allen et al., 2019;Brooks et al., 2010). In extreme cases transpired water can be many months or years old (Zhang et al., 2017); Generally, stored water is much older than the stream waters that drain them (Berghuijs & Kirchner, 2017)-with stream waters themselves often in the years to decades age range (McGuire & McDonnell, 2006).But while tracer data in streamflow is now relatively abundant (Penna et al., 2018;Sprenger et al., 2019) and available at high resolution (Rode et al., 2016;von Freyberg et al., 2017), a major share of the water balance still goes through an outlet that is almost unmonitored in terms of tracers: the transpiration flux.

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Section: The Age Of the Transpiration Fluxsupporting

confidence: 77%

Section: The Age Of the Transpiration Fluxsupporting

confidence: 72%

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Tracing and Closing the Water Balance in a Vegetated Lysimeter

Benettin

Nehemy

Asadollahi

et al. 2021

Water Resources Research

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“…The accuracy of the results is determined by the accuracy of key data like humidity and by how well the CG model describes the fractionated samples. For example, the dry experimental conditions around June 20 resulted in water stress conditions to the plant (see Nehemy et al, 2021) and during the same period the method tends to overestimate the true source, suggesting that the simple CG model may be insufficient to describe the evaporative enrichment in these circumstances. A full sensitivity analysis that explores the dependence of the results on model and data assumptions goes beyond this initial proof of concept, but would be the next critical follow-up to this preliminary work.…”

Section: Discussionmentioning

confidence: 99%

“…Since the leaf water sample lies farther away from the LMWL, the cloud of possible sources is larger.Yet, because the two samples lie roughly on the same evaporation line, the distributions of potential sources have similar means, i.e. the two samples likely originated from the same source.3 | METHODSTo test our approach, we used data from xylem and leaf water samples from two small willow trees (Salix viminalis), collected during a lysimeter experiment in May-June 2018 near Lausanne, CH(Nehemy et al, 2021). The willow-planted lysimeter was left open to natural precipitation for over 2 years.…”

mentioning

confidence: 99%

On the use of leaf water to determine plant water source: A proof of concept

Benettin

Nehemy

Cernusak

et al. 2021

Hydrological Processes

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Phloem water isotopically different to xylem water: Potential causes and implications for ecohydrological tracing

et al. 2022

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The stable isotopes of hydrogen and oxygen in xylem water are often used to investigate tree water sources. But this traditional approach does not acknowledge the contribution of water stored in the phloem to transpiration and how this may affect xylem water and source water interpretations. Additionally, there is a prevailing assumption that there is no isotope fractionation during tree water transport. Here, we systematically sampled xylem and phloem water at daily and subdaily resolutions in a large lysimeter planted with Salix viminalis. Stem diurnal change in phloem water storage and transpiration rates were also measured. Our results show that phloem water is significantly less enriched in heavy isotopes than xylem water. At subdaily resolution, we observed a larger isotopic difference between xylem and phloem during phloem water refilling and under periods of tree water deficit. These findings contrast with the expectation of heavy‐isotope enriched water in phloem due to downward transport of enriched leaf water isotopic signatures. Because of previous evidence of aquaporin mediated phloem and xylem water transport and higher osmotic permeability of lighter hydrogen isotopologues across aquaporins, we propose that radial water transport across the xylem–phloem boundary may drive the relative depletion of heavy isotopes in phloem and their relative enrichment in xylem.

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Tree water deficit and dynamic source water partitioning

Cited by 46 publications

References 137 publications

Tracing and Closing the Water Balance in a Vegetated Lysimeter

Tracing and Closing the Water Balance in a Vegetated Lysimeter

On the use of leaf water to determine plant water source: A proof of concept

Phloem water isotopically different to xylem water: Potential causes and implications for ecohydrological tracing

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