Unexplained hydrogen isotope offsets complicate the identification and quantification of tree water sources in a riparian forest

Hydrology and earth system sciences, Journal Year: 2019, Volume and Issue: 23(4), P. 2129 - 2146

Published: April 26, 2019

Abstract. We investigated plant water sources of an emblematic refugial population Fagus sylvatica (L.) in the Ciron river gorges south-western France using stable isotopes. It is generally assumed that no isotopic fractionation occurs during root uptake, so composition xylem effectively reflects source water. However, this assumption has been called into question by recent studies found that, at least some dates growing season, did not reflect any mixture potential sources. In context, highly resolved datasets covering a range environmental conditions could shed light on possible plant–soil processes responsible for phenomenon. study, hydrogen (δ2H) and oxygen (δ18O) isotope compositions all tree were measured fortnightly over entire season. Using Bayesian mixing model (MixSIAR), we then quantified relative contribution F. Quercus robur trees. Based δ18O data alone, both species used mix top deep soil with Q. deeper than sylvatica. The stream appeared to be marginal despite proximity trees stream, as already reported other riparian forests. Xylem always interpreted shallow waters, but δ2H was often more depleted considered argue unsaturated zone and/or within tissues underlie unexpected relatively water, observed halophytic xerophytic species. By means sensitivity analysis, estimation models strongly affected depletion. A better understanding what causes separation between urgently needed.

Language: Английский

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An explanation for the isotopic offset between soil and stem water in a temperate tree species

New Phytologist, Journal Year: 2020, Volume and Issue: 227(3), P. 766 - 779

Published: April 2, 2020

A growing number of field studies report isotopic offsets between stem water and its potential sources that prevent the unambiguous identification plant origin using isotopes. We explored causes this offset by conducting a controlled experiment on temperate tree species Fagus sylvatica. measured δ2 H δ18 O soil from potted saplings three substrates subjected to two watering regimes. Regardless substrate, were similar only near permanent wilting point. Under moister conditions, was 11 ± 3‰ more negative than H, coherent with studies. drier became progressively enriched H. Although broadly reflected water, soil-stem differences correlated (r = 0.76) increased transpiration rates indicated proxies. Soil-stem are likely be caused isotope heterogeneities within pore tissues, which would masked under conditions as result evaporative enrichment, fractionation root uptake. Our results challenge our current understanding signals in soil-plant continuum.

Language: Английский

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Water sources for root water uptake: Using stable isotopes of hydrogen and oxygen as a research tool in agricultural and agroforestry systems

Agriculture Ecosystems & Environment, Journal Year: 2019, Volume and Issue: 291, P. 106790 - 106790

Published: Dec. 27, 2019

Language: Английский

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Stable isotopes of water reveal differences in plant – soil water relationships across northern environments

Hydrological Processes, Journal Year: 2020, Volume and Issue: 35(1)

Published: Dec. 24, 2020

Abstract We compared stable isotopes of water in plant stem (xylem) and soil collected over a complete growing season from five well‐known long‐term study sites northern/cold regions. These spanned decreasing temperature gradient Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf (northern Canada). Xylem was isotopically depleted waters, most notably for deuterium. The degree which potential sources could explain the isotopic composition xylem assessed quantitatively using overlapping polygons enclose respective data sets when plotted dual isotope space. At angiosperms showed strong overlap with water; this not case gymnosperms. In cases, on given sampling day be better explained if considered longer antecedent periods spanning many months. at usually dissimilar drier summer months, although differed sequence change. Open questions remain why significant proportion cannot by sources, particularly It is recommended that future research focuses fractionation affect uptake soil‐root interface, both through effects exchange between vapour liquid phases mycorrhizal interactions. Additionally, cold regions, evaporation diffusion winter may an important process.

Language: Английский

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Digging deeper: what the critical zone perspective adds to the study of plant ecophysiology

New Phytologist, Journal Year: 2020, Volume and Issue: 226(3), P. 666 - 671

Published: Jan. 8, 2020

Summary The emergence of critical zone (CZ) science has provided an integrative platform for investigating plant ecophysiology in the context landscape evolution, weathering and hydrology. CZ lies between top vegetation canopy fresh, chemically unaltered bedrock plays a pivotal role sustaining life. We consider what perspective recently brought to study ecophysiology. specifically highlight novel research demonstrating importance deeper subsurface water nutrient relations. also point knowledge gaps opportunities, emphasising, particular, greater focus on roles deep, nonsoil resources how those influence coevolve with plants as frontier ecophysiological research.

Language: Английский

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Variation in the access to deep soil water pools explains tree-to-tree differences in drought-triggered dieback of Mediterranean oaks

Tree Physiology, Journal Year: 2020, Volume and Issue: 40(5), P. 591 - 604

Published: March 2, 2020

Individual differences in the access to deep soil water pools may explain differential damage among coexisting, conspecific trees as a consequence of drought-induced dieback. We addressed this issue by comparing responses severe drought three Mediterranean oak species with different tolerance, Quercus pubescens L. and frainetto Ten., mainly thriving at xeric mesic sites, respectively, cerris L., which dominates intermediate sites. For each species, we compared coexisting declining (D) non-declining (ND) trees. The stable isotope composition (δ2H, δ18O) xylem was used infer use sources. also measured tree size radial growth quantify long-term divergence wood production between D ND non-structural carbohydrates (NSCs) sapwood evaluate if presented lower NSC values. had deeper than except Q. frainetto, indicated significantly more depleted However, strong δ2H offset isotopes observed peak summer could suggest that both types were not physiologically active under extreme conditions. Alternative processes causing deuterium fractionation, however, be ruled out. Tree height recent (last 15-25 years) rates all studied 22 44%, respectively. Lastly, there consistent pattern concentration; pubescens, it higher while ones exhibiting concentration. conclude vulnerability oaks depends on pools, related rooting depth, rate.

Language: Английский

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In situ measurements of soil and plant water isotopes: a review of approaches, practical considerations and a vision for the future

Hydrology and earth system sciences, Journal Year: 2020, Volume and Issue: 24(9), P. 4413 - 4440

Published: Sept. 11, 2020

Abstract. The number of ecohydrological studies involving water stable isotope measurements has been increasing steadily due to technological (e.g., field-deployable laser spectroscopy and cheaper instruments) methodological (i.e., tracer approaches or improvements in root uptake models) advances recent years. This enables researchers from a broad scientific background incorporate water-isotope-based methods into their studies. Several effects are currently not fully understood but might be essential when investigating depths vegetation separating processes the soil–vegetation–atmosphere continuum. Different viewpoints exist on (i) extraction for soil plant artifacts potentially introduced by them, (ii) pools (mobile vs. immobile) measured with those methods, (iii) spatial variability temporal dynamics composition different compartments terrestrial ecosystems. In situ have proposed as an innovative necessary way address these issues required order disentangle take them account studying plants soil–plant–atmosphere interaction based isotopes. Herein, we review current status isotopes soils plants, point out highlight potential future research. Moreover, put strong focus practical aspects this provide guideline limited previous experience methods. We also include section opportunities incorporating data obtained described existing isotope-enabled models examples illustrating benefits doing so. Finally, propose integrated methodology measuring both carrying at authors shown that reliable can generated field using composition. For transpiration, common effort. Little attention paid xylem measurements. Research needs improving further developing There is need consistent combined (soils plants) Such systems should designed adapted environment studied. conclude many rely extensively because technical difficulty uncertainties. Future research aim simplified approach provides reasonable trade-off between practicability precision accuracy.

Language: Английский

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Using water stable isotopes to understand evaporation, moisture stress, and re-wetting in catchment forest and grassland soils of the summer drought of 2018

Hydrology and earth system sciences, Journal Year: 2020, Volume and Issue: 24(7), P. 3737 - 3752

Published: July 23, 2020

Abstract. In drought-sensitive lowland catchments, ecohydrological feedbacks to climatic anomalies can give valuable insights into ecosystem functioning in the context of alarming climate change projections. However, dynamic influences vegetation on spatio-temporal processes water cycling critical zone catchments are not yet fully understood. We used stable isotopes investigate impacts 2018 drought dominant soil–vegetation units mixed land use Demnitz Millcreek (DMC, north-eastern Germany) catchment (66 km2). The isotope sampling was carried out conjunction with hydroclimatic, soil, groundwater, and monitoring. Drying soils, falling groundwater levels, cessation streamflow, reduced crop yields demonstrated failure storage support “blue” (groundwater recharge stream discharge) “green” (evapotranspiration) fluxes. further conducted monthly bulk soil assess dynamics under forest grassland vegetation. Forest soils were drier than grassland, mainly due higher interception transpiration losses. also had more freely draining shallow layers dominated by rapid young (age <2 months) fluxes after rainfall events. retentive older >2 months), though lack deep percolation produced ages >1 year forest. found displacement any “drought signal” within profile limited isotopic signatures no or “memory effect” d-excess over time step, indicating mixing new rainfall. Our findings suggest that contrasting communities have distinct partitioning sub-surface. Such will be invaluable for developing sustainable management strategies appropriate availability building resilience change.

Language: Английский

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The determining factors of hydrogen isotope offsets between plants and their source waters

New Phytologist, Journal Year: 2024, Volume and Issue: 241(5), P. 2009 - 2024

Published: Jan. 5, 2024

Summary A fundamental assumption when using hydrogen and oxygen stable isotopes to understand ecohydrological processes is that no isotope fractionation occurs during plant water uptake/transport/redistribution. growing body of evidence has indicated in certain environments or for species. However, whether the source offset (δ 2 H offset) a common phenomenon how it varies among different climates functional types remains unclear. Here, we demonstrated presence positive, negative, zero offsets based on extensive observations 12 species 635 paired isotopic compositions along strong climate gradient within an inland river basin. Both temperature relative humidity affected δ offsets. In cool moist environments, mainly negatively due its role physiological activity. warm dry offsets, likely by impacting leaf stomatal conductance. These also showed substantial linkages with 18 O enrichment, indicator transpiration evaporative demand. Further studies focusing ecophysiological biochemical understanding dynamics under specific are essential regional conducting paleoclimate reconstructions.

Language: Английский

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UAV‐Based Land Surface Temperatures and Vegetation Indices Explain and Predict Spatial Patterns of Soil Water Isotopes in a Tropical Dry Forest

Water Resources Research, Journal Year: 2025, Volume and Issue: 61(2)

Published: Feb. 1, 2025

Abstract The spatial variation of soil water isotopes (SWI)—representing the baseline for investigating root uptake (RWU) depths with stable isotope techniques—has rarely been investigated. Here, we use SWI depth profile sampling in combination unmanned aerial vehicle (UAV) based land surface temperature estimates and vegetation indices (VI) order to improving process understanding relationships between variability content patterns canopy status, represented form VI. We carried out a 10 profiles tropical dry forest. UAV data were collected analyzed obtain detailed characterization status. then performed statistical analysis VI temperatures values at different resolutions (3 cm–5 m). Best used generating isoscapes entire study area. Results suggest that are strongly mediated by parameters (VI). Various correlate across all depths. depend on ( R 2 0.66 δ 18 O 0.64 H). Strongest overall correlations found resolution 0.5 m. speculate this might be ideal spatially characterizing investigate RWU forest environments. Supporting analyses UAV‐based approaches future avenue representation credibility such studies.

Language: Английский

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