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

Online (or: in situ) 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.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 (Marshall et al., 2019), namely &#8216;stem borehole equilibration&#8217;, was combined with online 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.Results show that &#8211; as expected &#8211; 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. &#160;However, no hydraulic redistribution was identified.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 &#8216;real&#8217; conditions.ReferencesMarshall, J.D., Cuntz, M., Beyer, M., Dubbert, M., K&#252;hnhammer, K., 2019. Borehole equilibration: testing a new method to monitor the isotopic composition of tree xylem water in situ. Front. Plant Sci.

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

10.5194/hess-2021-456 ◽

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.

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

10.5194/egusphere-egu2020-12504 ◽

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

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 (18O and 2H) 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 &#948;18O and &#948;2H; 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&#160;nm diameter) in 20&#160;&#181;mol/l solution with H2O 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 2H-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.

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Nighttime sap flow of Acacia mangium and its implications for nighttime transpiration and stem water storage

Journal of Plant Ecology ◽

10.1093/jpe/rtr025 ◽

2011 ◽

Vol 5 (3) ◽

pp. 294-304 ◽

Cited By ~ 25

Author(s):

H. Wang ◽

P. Zhao ◽

D. Holscher ◽

Q. Wang ◽

P. Lu ◽

...

Keyword(s):

Sap Flow ◽

Water Storage ◽

Acacia Mangium ◽

Nighttime Transpiration ◽

Stem Water ◽

Stem Water Storage

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A field study of depletion-replenish water storage mechanism in tree stems in semi-arid region

10.5194/egusphere-egu2020-14585 ◽

2020 ◽

Author(s):

Yiben Cheng ◽

Yunqi Wang ◽

Qunou Jiang

Keyword(s):

Soil Water ◽

Sap Flow ◽

Water Storage ◽

Growing Season ◽

Arid Areas ◽

Start Time ◽

Stem Water ◽

Stem Water Storage ◽

Semi Arid ◽

Tree Stem

Trees in arid and semi-arid regions are faced with water shortages at most times, and the use of water storage in tree stem is an important mechanism and pathway for adaptation to drought. In this research, we have explored the tree saplings in semi-arid areas by continuous monitoring and analysis of the sap flux at stem top and stem breast, in the main growth season. A primary objective is to find out when and how trees use stem water storage as a reservoir, and more specifically if there is a difference in stem flow start time between stem top and stem breast. Our study shows that in sunny day of the growing season, the sap flow at stem top start time is later than the sap flow at stem breast, with the maximum of time lag about 60 mins, and the daily sap flow peak time of stem top is later than that of the stem breast by 1-2 hrs. The maximum daily flux at stem top is about 1.4-2.1 times greater than that at stem breast. Stem water storage increases the drought tolerance of trees. The depletion stage of stem water storage mainly occurs in early morning, and then enters the replenishing phase in the afternoon. In a sunny day, with the increase of soil water deficit with relative extractable water (REW) (or the relative effective soil water index) less than 0.43, demand for water storage of stem is more significant, and its role is mainly based on the depletion process. When the soil moisture condition is improved, the process is dominated by replenishing. From the results of continuous observations throughout the growing season, the depleting and replenishing processes can achieve equilibrium in a short period of time (like a few days). This research has advanced our understanding of the utilization mechanism of tree stem storage water in semi-arid areas.

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Sap flow index as an indicator of water storage use

Journal of Hydrology and Hydromechanics ◽

10.1515/johh-2015-0013 ◽

2015 ◽

Vol 63 (2) ◽

pp. 124-133 ◽

Cited By ~ 4

Author(s):

Nadezhda Nadezhdina ◽

Jan Čermák ◽

Alec Downey ◽

Valeriy Nadezhdin ◽

Martti Perämäki ◽

...

Keyword(s):

Sap Flow ◽

Water Storage ◽

Relative Magnitude ◽

Continuous Heating ◽

Flow Index ◽

Oak Trees ◽

Picea Omorika ◽

Stem Water ◽

Stem Water Storage ◽

Daily Transpiration

Abstract Symmetrical temperature difference also known as the sap flow index (SFI) forms the basis of the Heat Field Deformation sap flow measurement and is simultaneously collected whilst measuring the sap flow. SFI can also be measured by any sap flow method applying internal continuous heating through the additional installation of an axial differential thermocouple equidistantly around a heater. In earlier research on apple trees SFI was found to be an informative parameter for tree physiological studies, namely for assessing the contribution of stem water storage to daily transpiration. The studies presented in this work are based on the comparative monitoring of SFI and diameter in stems of different species (Pseudotsuga menziesii, Picea omorika, Pinus sylvestris) and tree sizes. The ability of SFI to follow the patterns of daily stem water storage use was empirically confirmed by our data. Additionally, as the HFD multipointsensors can measure sap flow at several stem sapwood depths, their use allowed to analyze the use of stored water in different xylem layers through SFI records. Radial and circumferential monitoring of SFI on large cork oak trees provided insight into the relative magnitude and timing of the contribution of water stored in different sapwood layers or stem sectors to transpiration.

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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"

10.5194/hess-2021-456-supplement ◽

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

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Examination and parameterization of the root water uptake model from stem water potential and sap flow measurements

Hydrological Processes ◽

10.1002/hyp.9406 ◽

2012 ◽

pp. n/a-n/a ◽

Cited By ~ 3

Author(s):

Yuting Yang ◽

Huade Guan ◽

John L. Hutson ◽

Hailong Wang ◽

Caecilia Ewenz ◽

...

Keyword(s):

Water Potential ◽

Water Uptake ◽

Sap Flow ◽

Root Water Uptake ◽

Stem Water Potential ◽

Flow Measurements ◽

Stem Water ◽

Sap Flow Measurements

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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 ◽

10.5194/hess-24-4413-2020 ◽

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.

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