scholarly journals Xylem water in riparian Willow trees (Salix alba) reveals shallow sources of root water uptake by in situ monitoring of stable water isotopes

2021 ◽  
Author(s):  
Jessica Landgraf ◽  
Dörthe Tetzlaff ◽  
Maren Dubbert ◽  
David Dubbert ◽  
Aaron Smith ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Water Uptake ◽  
Sap Flow ◽  
Root Water Uptake ◽  
In Situ Monitoring ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Salix Alba

Abstract. Root water uptake is an important critical zone process, as plants can tap various water sources and transpire these back into the atmosphere. However, knowledge about the spatial and temporal dynamics of root water uptake and associated water sources at both high temporal resolution (e.g. daily) and over longer time periods (e.g. seasonal) is still limited. We used cavity ring-down spectroscopy (CRDS) for continuous in situ monitoring of stable water isotopes in soil and xylem water for two riparian willow (Salix alba) trees over the growing season (May to October) of 2020. This was complemented by isotopic sampling of local precipitation, groundwater and stream water in order to help constrain the potential sources of root water uptake. A local flux tower, together with sap flow monitoring, soil moisture measurements and dendrometry were also used to provide the hydroclimatic and ecohydrological contexts for in situ isotope monitoring. In addition, bulk samples of soil water and xylem water were collected to corroborate the continuous in situ data. The monitoring period was characterised by frequent inputs of precipitation, interspersed by warm dry periods which resulted in variable moisture storage in the upper 20 cm of the soil profile and dynamic isotope signatures. This variability was greatly damped in 40 cm and the isotopic composition of the sub-soil and groundwater was relatively stable. The isotopic composition and dynamics of xylem water was very similar to that of the upper soil and analysis using a Bayesian mixing model inferred that overall ~90 % of root water uptake was derived from the upper soil profile. Sap flow and dendrometry data indicated that soil water availability did not seriously limit transpiration during the study period, though there was a suggestion that deeper (> 40 cm) soil water might provide a higher proportion of root water uptake (~30 %) in a drier period in the late summer. The study demonstrates the utility of prolonged real time monitoring of natural stable isotope abundance in soil-vegetation systems, which has great potential for further understanding of ecohydrological partitioning under changing hydroclimatic conditions.

scholarly journals Temporal dynamics of tree xylem water isotopes: In-situ monitoring and modelling

2021 ◽  
Author(s):  
Stefan Seeger ◽  
Markus Weiler
Keyword(s):  
Soil Water ◽  
Temporal Dynamics ◽  
Length Distribution ◽  
In Situ Monitoring ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Root Tips ◽  
Water Age ◽  
Isotopic Signatures

Abstract. We developed a setup for a fully automated, high frequency in-situ monitoring system of the stable water isotopes Deuterium and 18O in soil water and tree xylem. The setup was tested for 12 weeks within an isotopic labelling experiment during a large artificial sprinkling experiment including three mature European beech (Fagus sylvatica) trees. Our setup allowed for one measurement every 12–20 minutes, enabling us to obtain about seven measurements per day for each of our 15 in-situ probes in the soil and tree xylem. While the labelling induced an abrupt step pulse in the soil water isotopic signature, it took seven to ten days until the isotopic signatures at the trees' stem bases reached their peak label concentrations and it took about 14 days until the isotopic signatures at 8 m stem height levelled off around the same values. During the experiment, we observed the effects of several rain events and dry periods on the xylem water isotopic signatures, which fluctuated between the measured isotopic signatures observed in the upper and lower soil horizons. In order to explain our observations, we combined an already existing root water uptake (RWU) model with a newly developed approach to simulate the propagation of isotopic signatures from the root tips to the stem base and further up along the stem. The key to a proper simulation of the observed short term dynamics of xylem water isotopes, was accounting for sap flow velocities and the flow path length distribution within the root and stem xylem. Our modelling framework allowed us to identify parameter values that relate to root depth, horizontal root distribution and wilting point. The insights gained from this study can help to improve the representation of stable water isotopes in trees within ecohydrological models and the prediction of transit time distribution and water age of transpiration fluxes.

Tracing dynamic water uptake and transport from root to canopy by online monitoring of water isotopes in an enclosed tropical forest in response to drought

2020 ◽  
Author(s):  
Kathrin Kuehnhammer ◽  
Joost van Haren ◽  
Angelika Kuebert ◽  
Maren Dubbert ◽  
Nemiah Ladd ◽  
...  
Keyword(s):  
Water Uptake ◽  
Deep Water ◽  
Sap Flow ◽  
Water Storage ◽  
Root Water Uptake ◽  
Water Isotopes ◽  
Hydraulic Redistribution ◽  
Stem Water ◽  
Stem Water Storage

<p><em>Online</em> (or: <em>in situ</em>) methods for measuring soil and plant water isotopes have been identified as an innovative and crucial step to address recently identified issues in studying water uptake using stable isotope techniques.</p><p>During a controlled three month drought and rewetting experiment at the Biosphere 2 (B2) enclosed rainforest, a recently developed online method for measuring stem water isotopes (<em>Marshall et al., 2019</em>), namely ‘stem borehole equilibration’, was combined with <em>online</em> monitoring of soil water isotopes and transpired water isotopes as well as sap flow and stem water storage. This enabled us to study root water uptake depths of different tree species and dynamic changes during the dry down and rewetting. After two months of drought, the system was supplied with isotopically labelled water (deuterated water) from down below via a pipe system spanning across the complete B2 rainforest in order to identify deep water uptake of the rainforest trees and hydraulic redistribution.</p><p>Results show that – as expected – all monitored trees responded to the drought by changing their root water uptake towards deeper soil depths while sap flow rates of most trees decreased. When rewetting the system, deep water uptake from the base of B2 (between 2.5m and 4m soil depth) was identified in all large, mature trees (Clitoria faichildiana, Hibiscus tilliaceus, Hura crepitans, Pachira aquatica). No deep water uptake was found in the smaller trees (mainly Pachira aquatica). Furthermore, stem water storage was notably different between species and affected their adaptation to drought and response to rewetting. The labelled water was also identified in the transpired water more than one month after re-starting rainfall at B2.  However, no hydraulic redistribution was identified.</p><p>The holistic approach for monitoring the interactions of soils and plants provides inevitable insights into the adaptation of (enclosed) rainforests under drought and might have implications for natural rainforests. In particular, the capability of large trees to develop deep roots and the role of stem water storage are important elements for adaptation to climatic changes and need to be studied further under ‘real’ conditions.</p><p><strong>References</strong></p><p>Marshall, J.D., Cuntz, M., Beyer, M., Dubbert, M., Kühnhammer, K., 2019. Borehole equilibration: testing a new method to monitor the isotopic composition of tree xylem water in situ. Front. Plant Sci.</p>

C-dots as a novel silica-based fluorescent nanoparticle tracer to investigate plant hydraulics

2020 ◽  
Author(s):  
Kanishka Singh ◽  
Benjamin Hafner ◽  
James Knighton ◽  
M. Todd Walter ◽  
Taryn Bauerle
Keyword(s):  
Water Uptake ◽  
Plant Tissue ◽  
Imaging System ◽  
Root Water Uptake ◽  
Nano Particles ◽  
Water Isotopes ◽  
Hydraulic Redistribution ◽  
Severe Drought ◽  
Stable Water Isotopes ◽  
Plant Hydraulics

<p>Forest cover exerts a significant control on the partitioning of precipitation between evapotranspiration and surface runoff. Thus, understanding how plants take up and transpire water in forested catchments is essential to predict flooding potential and hydrologic cycling. A growing literature underscores the importance of integrating whole-plant hydraulics, including such processes as the spatial variability of root distribution and the temporally dynamic nature of root water uptake by depth in understanding the relationship between changes in vegetation and hydrology. The analysis of stable isotopes of water (<sup>18</sup>O and <sup>2</sup>H) sourced from soils and plant tissue has enabled the estimation of tree root water uptake depths and water use strategies. Despite the general acceptance of stable water isotopic data to estimate plant hydraulic dynamics, this methodology imposes assumptions that may produce spurious results. For example, end member mixing analysis neglects time-delays during tree-water storage. Also, it is likely that hydraulic redistribution processes of plants, which transport water across soil depths and both into and out of plant tissue, modify δ<sup>18</sup>O and δ<sup>2</sup>H; the isotopic signature of a collected sample may thus reflect a history of transport and exposure to fractionating processes not accounted for in analysis. We tested the feasibility of C-dots, core-shell silica polyethylene-glycol coated fluorescent nano-particles (5.1 nm diameter) in 20 µmol/l solution with H<sub>2</sub>O labeled with a near-infrared fluorophore, cyanine 5.5 (excitation maximum of 646 nm, emission maximum of 662 nm), as an alternative to stable water isotopes in the investigation of plant hydraulics. We examined the absorption and transport of C-dots through soil, as well as roots and aerial structures of Eastern hemlock (Tsuga canadensis), Eastern white pine (Pinus strobus), and white spruce (Picea glauca) saplings (n = 12 each) via an IVIS-200 luminescence in-situ imaging system. We compared the fluid mechanics, residence times and mixing schemes of C-dots with <sup>2</sup>H-labeled water during transport within these plant species to establish the nanoparticles as a viable alternative through a split-root hydraulic redistribution experiment under moderate and severe drought conditions. We present a residence-time distribution to elucidate the mixing scheme of C-dot solution and calibration curves to aid future studies. This research is the premier assessment of this nanoparticle as an alternative tracer to stable water isotopes, and as such may yield insights for broader applications.</p>

scholarly journals Diurnal variation in xylem water isotopic signature biases depth of root-water uptake estimates

2019 ◽  
Author(s):  
Hannes De Deurwaerder ◽  
Marco D. Visser ◽  
Matteo Detto ◽  
Pascal Boeckx ◽  
Félicien Meunier ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Soil Water ◽  
Water Uptake ◽  
Sap Flow ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Isotopic Signature ◽  
Stem Length ◽  
Individual Plant ◽  
List Type

SummaryStable water isotopes are a powerful and widely used tool to derive the depth of root water uptake (RWU) in lignified plants. Uniform xylem water isotopic signature (i-H2O-xyl) along the length of a lignified plant is a central assumption, which has never been properly evaluated.Here we studied the effects of diurnal variation in RWU, sap flow velocity and various other soil and plant parameters on i-H2O-xyl signature within a plant using a mechanistic plant hydraulic model.Our model predicts significant variation in i-H2O-xyl along the full length of an individual plant arising from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in i-H2O-xyl emerge between individuals with different sap flow velocities. We corroborated our model predictions with field observations from French Guiana and northwestern China. Modelled i-H2O-xyl varied considerably along stem length ranging up to 18.3‰ in δ2H and 2.2‰ in δ18O, largely exceeding the range of measurement error.Our results show clear violation of the fundamental assumption of uniform i-H2O-xyl and occurrence of significant biases when using stable isotopes to assess RWU. As a solution, we propose to include monitoring of sap flow and soil water potential for more robust RWU depth estimates.

Using natural abundances of stable water isotopes to constrain vertically distributed root water uptake of forest trees

2021 ◽  
Author(s):  
Fabian Bernhard ◽  
Katrin Meusburger
Keyword(s):  
Soil Water ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Hydrologic Model ◽  
Stable Water Isotopes ◽  
Isotopic Signatures ◽  
Sampling Campaign ◽  
Forest Sites ◽  
First Results ◽  
Trace Water

<p>The water balance in forest soils is strongly affected by vertical distribution of root water uptake. Our objective is to constrain the parametrization of root water uptake in the field by using the naturally occurring, seasonal variability in stable isotope signatures in precipitation to trace water fluxes through the soil and into the trees.</p> <p>The 1D soil hydrologic model LWFBrook90.jl contains the necessary processes to accurately reproduce hydrometric observations of volumetric soil moisture content and soil matric potential at forest sites in Switzerland. Root water uptake is described with a gradient-driven model using vertically varying root density and moisture-dependent rhizosphere resistivities. The hydrologic model will be extended with transport and fractionation processes to enable the modeling of isotopic signatures in soil and tree water.</p> <p>We present a planned field sampling campaign over two subsequent vegetation seasons at 10 long-term monitoring forest sites. Soil water is sampled with lysimeters at four soil depths, and tree water is sampled from the xylem with increment corers. Both types of samples are taken bi-weekly. First results from an ongoing multi-year soil water sampling campaign show that the signal can be traced along the soil profile and are presented to illustrate the approach.</p>

scholarly journals Insights into the isotopic mismatch between bulk soil water and <i>Salix matsudana</i> Koidz trunk water from root water stable isotope measurements

2021 ◽  
Vol 25 (7) ◽  
pp. 3975-3989
Author(s):  
Ying Zhao ◽  
Li Wang
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Water Uptake ◽  
Soil Depth ◽  
Experimental Period ◽  
Root Water Uptake ◽  
Bulk Soil ◽  
Mobile Water ◽  
Isotopic Compositions ◽  
Salix Matsudana

Abstract. Increasing numbers of field studies have detected isotopic mismatches between plant trunk water and its potential sources. However, the cause of these isotopic offsets is not clear, and it is uncertain whether they occur during root water uptake or during water transmission from root to trunk. Thus, we measured the specific isotopic composition (δ2H and δ18O) of each component (e.g. bulk soil water, mobile water, groundwater, trunk water and root water of Salix matsudana Koidz trees) in the soil–root–trunk continuum with a resolution of about 3 days. We report three main findings. First, we detected a clear separation between the isotopic compositions of mobile water and bulk soil water, but the distinction between mobile water and bulk soil water gradually decreased with increasing soil depth. Second, root water composition deviated from bulk soil water isotopic composition but overlapped with the composition derived for less mobile water. The maximum differences in δ2H and δ18O between bulk soil water and root water were −8.6 ‰ and −1.8 ‰, respectively. Third, trunk water was only isotopically similar to root water at 100–160 cm depths, and it remained stable during the experimental period, suggesting that the trees consistently used the stable deep water source. In conclusion, the isotopic offset between bulk soil water and trunk water of S. matsudana reflected an isotopic mismatch between root water and bulk soil water associated with the heterogeneity of the soil water. Our results illuminate relationships between the isotopic compositions of soil waters of various mobilities, root water and trunk water that may be useful for advancing our understanding of root water uptake and transport.

In-situ monitoring of soil water isotopic composition for partitioning of evapotranspiration during one growing season of sugar beet (Beta vulgaris)

2019 ◽  
Vol 266-267 ◽  
pp. 53-64 ◽  
Author(s):  
Maria Quade ◽  
Anne Klosterhalfen ◽  
Alexander Graf ◽  
Nicolas Brüggemann ◽  
Normen Hermes ◽  
...  
Keyword(s):  
Sugar Beet ◽  
Isotopic Composition ◽  
Soil Water ◽  
Beta Vulgaris ◽  
Growing Season ◽  
In Situ Monitoring

Isotope labeling experiment to infer ecohydrological travel times

2020 ◽  
Author(s):  
David Mennekes ◽  
Michael Rinderer ◽  
Stefan Seeger ◽  
Hugo de Boer ◽  
Natalie Orlowski ◽  
...  
Keyword(s):  
Soil Water ◽  
Water Uptake ◽  
Temporal Resolution ◽  
Water Vapor Pressure ◽  
Root Water Uptake ◽  
Field Conditions ◽  
High Temporal Resolution ◽  
Travel Times ◽  
Isotope Measurements

&lt;p&gt;Stable water isotopes are promising tracers to study soil-tree interactions and root water uptake. Traditionally, destructive sampling techniques are applied to measure the isotopic signature in soils and plant tissues but these methods are limited in their temporal resolution. For calculating ecohydrological travel times from soil water to transpiration, high frequent isotope measurements are required. Recently, in-situ water isotope probes have been successfully applied in beech trees to yield high-frequent isotope measurements under field conditions but the complexity and heterogeneity of natural field conditions can make a systematical method testing difficult. Here, we test whether the new probes are capable of capturing tree species-specific differences in root water uptake and associated travel times.&lt;br&gt;We test this in a controlled experiment using large pots with three 4-6 meter high and 20 year old coniferous and deciduous trees: &lt;em&gt;Pinus pinea&lt;/em&gt;, &lt;em&gt;Alnus&lt;/em&gt; &lt;em&gt;x spaethii&lt;/em&gt; and &lt;em&gt;Quercus&lt;/em&gt; &lt;em&gt;suber&lt;/em&gt; that are expected to have different water uptake strategies. We applied deuterated irrigation water to the homogeneous soils in the pots and traced the water flux from the soils through the trees with in-situ isotope probes in high temporal resolution.&lt;br&gt;This contribution presents preliminary results on ecohydrological travel times in relation to environmental parameters such as sap flow, photosynthetic activity, matrix potential, soil water content, water vapor pressure deficit and solar radiation.&lt;br&gt;Our in-situ isotope probes were capable to capture the breakthrough of the isotope tracer in all trees. The calculated travel times were shorter for the Pinus and Alnus compared to the Quercus which suggests differences in root water uptake. Detailed results from such controlled experiments are fundamental for testing new measurement techniques such as the in-situ isotope probes. Such results are important to better interpret results measured under natural and therefore more complex and heterogeneous field conditions.&lt;/p&gt;

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