scholarly journals Causes and consequences of pronounced variation in the isotope composition of plant xylem water

2020 ◽  
Vol 17 (19) ◽  
pp. 4853-4870
Author(s):  
Hannes P. T. De Deurwaerder ◽  
Marco D. Visser ◽  
Matteo Detto ◽  
Pascal Boeckx ◽  
Félicien Meunier ◽  
...  
Keyword(s):  
Woody Plants ◽  
Isotope Composition ◽  
Root Water Uptake ◽  
Stem Length ◽  
Environmental Drivers ◽  
Sap Flux ◽  
Matric Potential ◽  
Sap Flux Density ◽  
Hydrogen And Oxygen Isotope ◽  
Water Isotopologues

Abstract. Stable isotopologues of water are widely used to derive relative root water uptake (RWU) profiles and average RWU depth in lignified plants. Uniform isotope composition of plant xylem water (δxyl) along the stem length of woody plants is a central assumption of the isotope tracing approach which has never been properly evaluated. Here we evaluate whether strong variation in δxyl within woody plants exists using empirical field observations from French Guiana, northwestern China, and Germany. In addition, supported by a mechanistic plant hydraulic model, we test hypotheses on how variation in δxyl can develop through the effects of diurnal variation in RWU, sap flux density, diffusion, and various other soil and plant parameters on the δxyl of woody plants. The hydrogen and oxygen isotope composition of plant xylem water shows strong temporal (i.e., sub-daily) and spatial (i.e., along the stem) variation ranging up to 25.2 ‰ and 6.8 ‰ for δ2H and δ18O, respectively, greatly exceeding the measurement error range in all evaluated datasets. Model explorations predict that significant δxyl variation could arise from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in δxyl emerge between individuals that differ only in sap flux densities or are monitored at different times or heights. This work shows a complex pattern of δxyl transport in the soil–root–xylem system which can be related to the dynamics of RWU by plants. These dynamics complicate the assessment of RWU when using stable water isotopologues but also open new opportunities to study drought responses to environmental drivers. We propose including the monitoring of sap flow and soil matric potential for more robust estimates of average RWU depth and expansion of attainable insights in plant drought strategies and responses.

scholarly journals Diurnal variation in the isotope composition of plant xylem water biases the depth of root-water uptake estimates

2020 ◽  
Author(s):  
Hannes P. T. De Deurwaerder ◽  
Marco D. Visser ◽  
Matteo Detto ◽  
Pascal Boeckx ◽  
Félicien Meunier ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Soil Water ◽  
Water Uptake ◽  
Isotope Composition ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Stem Length ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Water Isotopologues

Abstract. 1. Stable isotopologues of water are a widely used tool to derive the depth of root water uptake (RWU) in lignified plants. Uniform isotope composition of plant xylem water (i-H2O-xyl) along the stem length is a central assumption, which has never been properly evaluated. 2. We studied the effects of diurnal variation in RWU, sap flux density and various other soil and plant parameters on i-H2O-xyl within a plant using a mechanistic plant hydraulic model and empirical field observations from French Guiana and northwestern China. 3. Our model predicts significant i-H2O-xyl variation arising from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in i-H2O-xyl emerge between individuals with different sap flux densities. In line with model predictions, field data show excessive i-H2O-xyl variation during the day or along stem length ranging up to 25.2 ‰ in δ2H and 6.8 ‰ in δ18O, largely exceeding the measurement error range. 4. Our work show that the fundamental assumption of uniform i-H2O-xyl is violated both theoretically and empirically and therefore a real danger exists of significant biases when using stable water isotopologues to assess RWU. We propose to include monitoring of sap flow and soil water potential for more robust RWU depth estimates.

scholarly journals The Depth of Water Taken up by Walnut Trees during Different Phenological Stages in an Irrigated Arid Hilly Area in the Taihang Mountains

Forests ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 121 ◽  
Author(s):  
Yang Liu ◽  
Xuemei Zhang ◽  
Shuang Zhao ◽  
Huabing Ma ◽  
Guohui Qi ◽  
...  
Keyword(s):  
Soil Water ◽  
Soil Depth ◽  
Isotope Composition ◽  
Irrigation Management ◽  
Soil Layer ◽  
Root Water Uptake ◽  
Phenological Stages ◽  
Hilly Area ◽  
Fruit Maturity ◽  
Hydrogen And Oxygen Isotope

Understanding how the soil environment impacts root water uptake location and magnitude is important for better management of plant irrigation. In this study, stable hydrogen and oxygen isotope composition were used to determine seasonal variations in the depth of water taken up by walnut trees during different phenological stages in an irrigated arid hilly area in the Taihang Mountains in China. The contributions of soil water at different depths to the water taken up were quantified by the MixSIAR Bayesian isotope mixing model. The results indicated that water taken up by the walnut trees was sourced mainly from soil water in the 0–20 cm soil layer at the sprouting and leaf expansion stages (62.95%), and the 20–40 cm soil layer at blossoming and fruit-bearing (43.45%), fruit expansion (41.8%), and fruit maturity (39.15%) stages. The mean soil depth of the water taken up by the walnut trees gradually decreased as the phenological stages advanced. The proportions of various soil layer water contributions to the walnut trees differed throughout the phenological stages, and the proportion of deeper soil water contributions gradually increased as the phenological stages of walnut trees advanced. The results of the present study indicated that water sources for walnut trees varied by depth during different phenological stages. In addition to soil moisture, soil temperature may also be an important factor affecting the depth of water taken up by walnut trees. The results also provided scientific implications for water-saving irrigation management.

Stable Hydrogen and Oxygen Isotope Composition of Waters from Mine Tailings in Different Climatic Environments

2007 ◽  
Vol 41 (6) ◽  
pp. 1870-1876 ◽  
Author(s):  
Jorge E. Spangenberg ◽  
Bernhard Dold ◽  
Marie-Louise Vogt ◽  
Hans-Rudolf Pfeifer
Keyword(s):  
Oxygen Isotope ◽  
Mine Tailings ◽  
Isotope Composition ◽  
Oxygen Isotope Composition ◽  
Hydrogen And Oxygen Isotope

scholarly journals Evapotranspiration seasonality across the Amazon basin

2017 ◽  
Author(s):  
Eduardo Eiji Maeda ◽  
Xuanlong Ma ◽  
Fabien Wagner ◽  
Hyungjun Kim ◽  
Taikan Oki ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Regional Climate ◽  
Root Water Uptake ◽  
Environmental Drivers ◽  
Seasonal Patterns ◽  
Wet Season ◽  
Important Indicator ◽  
Seasonally Dry ◽  
Basin Scale ◽  
Terrestrial Water

Abstract. Evapotranspiration (ET) of Amazon forests is a main driver of regional climate patterns and an important indicator of ecosystem functioning. Despite its importance, the seasonal variability of ET over Amazon forests, and its relationship with environmental drivers, is still poorly understood. In this study, we carry out a water balance approach to analyse seasonal patterns in ET and their relationships with water and energy drivers over five sub-basins across the Amazon basin. We used in-situ measurements of river discharge, and remotely sensed estimates of terrestrial water storage, rainfall, and solar radiation. We show that the characteristics of ET seasonality in all sub-basins differ in timing and magnitude. The highest mean annual ET was found in the northern Rio Negro basin (~ 1497 mm year−1) and the lowest values in the Solimões River basin (~ 986 mm year−1). For the first time in a basin-scale study, using observational data, we show that factors limiting ET vary across climatic gradients in the Amazon, confirming local-scale eddy covariance studies. Both annual mean and seasonality in ET are driven by a combination of energy and water availability, as neither rainfall nor radiation alone could explain patterns in ET. In southern basins, despite seasonal rainfall deficits, deep root water uptake allows increasing rates of ET during the dry season, when radiation is usually higher than in the wet season. We demonstrate contrasting ET seasonality with satellite greenness across Amazon forests, with strong asynchronous relationships in ever-wet watersheds, and positive correlations observed in seasonally dry watersheds. Finally, we compared our results with estimates obtained by two ET models, and we conclude that neither of the two tested models could provide a consistent representation of ET seasonal patterns across the Amazon.

scholarly journals Assessing variation in the radial profile of sap flux density in Pinus species and its effect on daily water use

2004 ◽  
Vol 24 (3) ◽  
pp. 241-249 ◽  
Author(s):  
C. R. Ford ◽  
M. A. McGuire ◽  
R. J. Mitchell ◽  
R. O. Teskey
Keyword(s):  
Flux Density ◽  
Water Use ◽  
Radial Profile ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Pinus Species ◽  
Daily Water

scholarly journals Erratum to: Changes in stem water content influence sap flux density measurements with thermal dissipation probes

Trees ◽  
2014 ◽  
Vol 28 (6) ◽  
pp. 1867-1868
Author(s):  
Lidewei L. Vergeynst ◽  
Maurits W. Vandegehuchte ◽  
Mary Anne McGuire ◽  
Robert O. Teskey ◽  
Kathy Steppe
Keyword(s):  
Water Content ◽  
Flux Density ◽  
Thermal Dissipation ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Density Measurements ◽  
Stem Water

A Direct Method for Estimating the Average Sap Flux Density Using a Modified Granier Measuring System

1997 ◽  
Vol 24 (5) ◽  
pp. 701 ◽  
Author(s):  
Ping Lu
Keyword(s):  
Flux Density ◽  
Sap Flow ◽  
Direct Method ◽  
Estimation Error ◽  
Original Method ◽  
Measuring System ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Average Value ◽  
Modified Method

The Granier sap flow measuring system that normally uses one analogue input channel of a datalogger for each sensor was modified to enable one channel to measure the average value of signals from two or more sensors. The sap flux density calculated from this average value of signals was very close (difference < 6.0%) to the arithmetic mean of the sap flux densities measured separately by means of individual sensors (using two or more input channels). The dynamics of the sap flux density measured by the modified method were similar to those measured by the original method. On a per-channel basis, the modified method reduced the ‘estimation error’ of sap flux density by 4–14-fold compared to the original method. By using the modified Granier system, the error in sap flow measurement that is usually associated with limited sampling can be substantially reduced without the need for extra dataloggers, the greatest item of expense.

The importance of conduction versus convection in heat pulse sap flow methods

2020 ◽  
Vol 40 (5) ◽  
pp. 683-694
Author(s):  
Michael A Forster
Keyword(s):  
Flux Density ◽  
Sap Flow ◽  
Peclet Number ◽  
Velocity Measurement ◽  
Measurement Range ◽  
Heat Pulse ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Péclet Number ◽  
Fast Methods

Abstract Heat pulse methods are a popular approach for estimating sap flow and transpiration. Yet, many methods are unable to resolve the entire heat velocity measurement range observable in plants. Specifically, the Heat Ratio (HRM) and Tmax heat pulse methods can only resolve slow and fast velocities, respectively. The Dual Method Approach (DMA) combines optimal data from HRM and Tmax to output the entire range of heat velocity. However, the transition between slow and fast methods in the DMA currently does not have a theoretical solution. A re-consideration of the conduction/convection equation demonstrated that the HRM equation is equivalent to the Péclet equation which is the ratio of conduction to convection. This study tested the hypothesis that the transition between slow and fast methods occurs when conduction/convection, or the Péclet number, equals one, and the DMA would be improved via the inclusion of this transition value. Sap flux density was estimated via the HRM, Tmax and DMA methods and compared with gravimetric sap flux density measured via a water pressure system on 113 stems from 15 woody angiosperm species. When the Péclet number ≤ 1, the HRM yielded accurate results and the Tmax was out of range. When the Péclet number &gt; 1, the HRM reached a maximum heat velocity at approximately 15 cm hr −1 and was no longer accurate, whereas the Tmax yielded accurate results. The DMA was able to output accurate data for the entire measurement range observed in this study. The linear regression analysis with gravimetric sap flux showed an r2 of 0.541 for HRM, 0.879 for Tmax and 0.940 for DMA. With the inclusion of the Péclet equation, the DMA resolved the entire heat velocity measurement range observed across 15 taxonomically diverse woody species. Consequently, the HRM and Tmax are redundant sap flow methods and have been superseded by the DMA.

scholarly journals Contribution of Advanced Regeneration of Pinus radiata D. Don. to Transpiration by a Fragment of Native Forest in Central Chile Is out of Proportion with the Contribution to Sapwood Area

Forests ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 187
Author(s):  
Don A. White ◽  
Richard P. Silberstein ◽  
Francisco Balocchi-Contreras ◽  
Juan Jose Quiroga ◽  
Pablo Ramírez de Arellano
Keyword(s):  
Climate Change ◽  
Leaf Area ◽  
Flux Density ◽  
Pinus Radiata ◽  
Native Forest ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Sapwood Area ◽  
Central Chile ◽  
Potential Index

The transpiration of Nothofagus glauca (Phil.) Krasser and advanced Pinus radiata D. Don. regeneration was measured in a fragment of native N. glauca forest. Over the eight months of this study, P. radiata contributed approximately 60% of the total stand transpiration. This was out of proportion with the approximately 34% of the stand sapwood area contributed by P. radiata. This was due to the significantly greater sap flux density of the P. radiata compared to the N. glauca between May and October. Though the results are from a small study conducted as part of a larger experiment, it is argued that they suggest that invasion by P. radiata may substantially increase the risk from climate change to reserves of N. glauca forest in the Maule region of central Chile. In some reserves of N. glauca forest, Forestal Arauco S.A. manually removed P. radiata that regenerated after the wildfire of January 2017. This was a costly operation and there is a need for indices to assess competition. The ratio of sapwood area to leaf area is suggested as a potential index for assessing competition to identify stands at risk.

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