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

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

10.5194/bg-2016-451 ◽

2016 ◽

Author(s):

Arndt Piayda ◽

Maren Dubbert ◽

Rolf Siegwolf ◽

Matthias Cuntz ◽

Christiane Werner

Keyword(s):

Soil Water ◽

Water Use ◽

Water Uptake ◽

Water Loss ◽

Cork Oak ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Herbaceous Vegetation ◽

Understory Plants ◽

Dry Conditions

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 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 labeled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on 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 evapotranspiration were quantified. Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive water loss for biomass production, carbon sequestration and nitrogen fixation. During the experiment no adjustments of main root water uptake depth to changes of water availability could be observed, rendering light to medium precipitation events under dry conditions useless. This forces understory plants to compete with adjacent trees for soil water in deeper soil layers. Thus understory plants are faster subject to chronic drought, leading to premature senescence at the onset of drought. Despite this water competition, the presence of Cork oak trees fosters infiltration to large degrees. That reduces drought stress, caused by evapotranspiration, due to favourable micro climatic conditions under tree crown shading. This study highlights complex soil – plant – atmosphere and inter – species interactions in both space and time controlling the fate of rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

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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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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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Variability in tree water uptake determined with stable water isotopes in an African tropical montane forest

Ecohydrology ◽

10.1002/eco.2278 ◽

2021 ◽

Author(s):

Melanie Hahn ◽

Suzanne Robin Jacobs ◽

Lutz Breuer ◽

Mariana C. Rufino ◽

David Windhorst

Keyword(s):

Water Uptake ◽

Montane Forest ◽

Water Isotopes ◽

Tropical Montane Forest ◽

Stable Water Isotopes

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Water uptake of riparian plants in the lower Lhasa River Basin, South Tibetan Plateau using stable water isotopes

Hydrological Processes ◽

10.1002/hyp.13831 ◽

2020 ◽

Vol 34 (16) ◽

pp. 3492-3505

Author(s):

Wenbo Rao ◽

Xi Chen ◽

Karina T. Meredith ◽

Hongbing Tan ◽

Man Gao ◽

...

Keyword(s):

Tibetan Plateau ◽

River Basin ◽

Water Uptake ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Riparian Plants ◽

Lhasa River Basin ◽

Lhasa River

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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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