scholarly journals Supplementary material to "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):  
Water Uptake ◽  
Root Water Uptake ◽  
In Situ Monitoring ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Salix Alba ◽  
Supplementary Material ◽  
Willow Trees

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.

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 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.

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

2020 ◽  
Vol 24 (9) ◽  
pp. 4413-4440
Author(s):  
Matthias Beyer ◽  
Kathrin Kühnhammer ◽  
Maren Dubbert
Keyword(s):  
Water Uptake ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Root Water Uptake ◽  
Water Isotopes ◽  
Future Research ◽  
Plant Water ◽  
In Situ Methods ◽  
Water Isotope

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

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>

scholarly journals Quantification of dynamic soil–vegetation feedbacks following an isotopically labelled precipitation pulse

2017 ◽  
Vol 14 (9) ◽  
pp. 2293-2306 ◽  
Author(s):  
Arndt Piayda ◽  
Maren Dubbert ◽  
Rolf Siegwolf ◽  
Matthias Cuntz ◽  
Christiane Werner
Keyword(s):  
Water Use ◽  
Water Uptake ◽  
Soil Evaporation ◽  
Cork Oak ◽  
Water Infiltration ◽  
Arid Ecosystems ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Herbaceous Vegetation ◽  
Understorey Plants

Abstract. The presence of vegetation alters hydrological cycles of ecosystems. Complex plant–soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and a pivotal foundation for understanding the carbon cycle of semi-arid ecosystems. Stable water isotopes can be used in this context as tracer to quantify water movement through soil–vegetation–atmosphere interfaces. The aim of this study is to disentangle vegetation effects on soil water infiltration and distribution as well as dynamics of soil evaporation and grassland water use in a Mediterranean cork oak woodland during dry conditions. An irrigation experiment using δ18O labelled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on the infiltration and distribution of event water in the soil profile. Dynamic responses of soil and herbaceous vegetation fluxes to precipitation regarding event water use, water uptake depth plasticity, and contribution to ecosystem soil evaporation and transpiration were quantified. Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive evaporation for transpiration, but infiltration rates decreased. No adjustments of main root water uptake depth to changes in water availability could be observed during the experiment. This forces understorey plants to compete with adjacent trees for water in deeper soil layers at the onset of summer. Thus, understorey plants are subjected to chronic water deficits faster, leading to premature senescence at the onset of drought. Despite this water competition, the presence of cork oak trees fosters infiltration and reduces evapotranspirative water losses from the understorey and the soil, both due to altered microclimatic conditions under crown shading. This study highlights complex soil–plant–atmosphere and inter-species interactions controlling rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

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