Internal water storage buffering maintains plant function under drought as described by a general hydraulic model

Internal water storage is of crucial importance for plants under drought stress, allowing them to temporarily maintain transpiration higher than root-uptake flow, thus potentially keeping a positive carbon balance. A deep understanding of this adaptation is key for predicting the fate of ecosystems subjected to climate change-induced droughts of increasing intensity and duration. Using a minimalistic model, we derive predictions for how environmental drivers (atmospheric demand and soil water availability) interplay with the water storage, creating time lags between the flows in the plant, and granting the plant increased hydraulic safety margin protecting its xylem from embolism. We parametrize our model against transpiration and sap flow measurements in a semi-arid pine forest during seasonal drought. From the parametrized whole-stand traits, we derive a 3.7-hour time lag between transpiration and sap flow, and that 31% of daily transpiration comes directly from the plant's internal water storage, both corroborated by the measurements. Due to the model simplicity, our results are useful for interpreting, analyzing, and predicting the effects of the internal storage buffering from the individual plant to the ecosystem scale. Because internal storage produces survival-enhancing behavior in sub-daily time scales, it is an indispensable component for modeling ecosystems under drought stress.

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Hydraulic architecture and internal water storage of Japanese cypress using measurements of sap flow and water potential

Ecohydrology ◽

10.1002/eco.2325 ◽

2021 ◽

Author(s):

Mai Kamakura ◽

Kenji Tsuruta ◽

Wakan A. Azuma ◽

Yoshiko Kosugi

Keyword(s):

Water Potential ◽

Sap Flow ◽

Water Storage ◽

Hydraulic Architecture ◽

Japanese Cypress ◽

Internal Water

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Estimation of canopy water storage capacity from sap flow measurements in a Bornean tropical rainforest

Journal of Hydrology ◽

10.1016/j.jhydrol.2008.01.020 ◽

2008 ◽

Vol 352 (3-4) ◽

pp. 288-295 ◽

Cited By ~ 14

Author(s):

Tomonori Kume ◽

Odair J. Manfroi ◽

Koichiro Kuraji ◽

Nobuaki Tanaka ◽

Toshinobu Horiuchi ◽

...

Keyword(s):

Sap Flow ◽

Tropical Rainforest ◽

Storage Capacity ◽

Water Storage ◽

Flow Measurements ◽

Water Storage Capacity ◽

Sap Flow Measurements ◽

Canopy Water

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Impact of Water Deficit on Seasonal and Diurnal Dynamics of European Beech Transpiration and Time-Lag Effect between Stand Transpiration and Environmental Drivers

Water ◽

10.3390/w12123437 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3437

Author(s):

Paulína Nalevanková ◽

Zuzana Sitková ◽

Jíři Kučera ◽

Katarína Střelcová

Keyword(s):

Soil Water ◽

Water Deficit ◽

Sap Flow ◽

Time Lag ◽

Global Radiation ◽

Environmental Drivers ◽

Time Lags ◽

Soil Water Deficit ◽

The Relationship

In-situ measurements of tree sap flow enable the analysis of derived forest transpiration and also the water state of the entire ecosystem. The process of water transport (by sap flow) and transpiration through vegetation organisms are strongly influenced by the synergistic effect of numerous external factors, some of which are predicted to alter due to climate change. The study was carried out by in-situ monitoring sap flow and related environmental factors in the years 2014 and 2015 on a research plot in Bienska dolina (Slovakia). We evaluated the relationship between derived transpiration of the adult beech (Fagus sylvatica L.) forest stand, environmental conditions, and soil water deficit. Seasonal beech transpiration (from May to September) achieved 59% of potential evapotranspiration (PET) in 2014 and 46% in 2015. Our study confirmed that soil water deficit leads to a radical limitation of transpiration and fundamentally affects the relationship between transpiration and environmental drivers. The ratio of transpiration (E) against PET was significantly affected by a deficit of soil water and in dry September 2015 decreased to the value of 0.2. The maximum monthly value (0.8) of E/PET was recorded in August and September 2014. It was demonstrated that a time lag exists between the course of transpiration and environmental factors on a diurnal basis. An application of the time lags within the analysis increased the strength of the association between transpiration and the variables. However, the length of these time lags changed in conditions of soil drought (on average by 25 min). Transpiration is driven by energy income and connected evaporative demand, provided a sufficient amount of extractable soil water. A multiple regression model constructed from measured global radiation (RS), air temperature (AT), and air humidity (RH) explained 69% of the variability in beech stand transpiration (entire season), whereas (RS) was the primary driving force. The same factors that were shifted in time explained 73% of the transpiration variability. Cross-correlation analysis of data measured in time without water deficit demonstrated a tighter dependency of transpiration (E) on environmental drivers shifted in time (−60 min RS, +40 min RH and +20 min vapour pressure deficit against E). Due to an occurrence and duration of soil water stress, the dependence of transpiration on the environmental variables became weaker, and at the same time, the time lags were prolonged. Hence, the course of transpiration lagged behind the course of global radiation by 60 (R2 = 0.76) and 80 (R2 = 0.69) minutes in conditions without and with water deficit, respectively.

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Global transpiration data from sap flow measurements: the SAPFLUXNET database

10.5194/essd-2020-227 ◽

2020 ◽

Author(s):

Rafael Poyatos ◽

Víctor Granda ◽

Víctor Flo ◽

Mark A. Adams ◽

Balázs Adorján ◽

...

Keyword(s):

Time Series ◽

Sap Flow ◽

Structural Characteristics ◽

Vapour Pressure Deficit ◽

Environmental Drivers ◽

Plant Responses ◽

Flow Measurements ◽

Automatic Data ◽

Plant Transpiration ◽

Sap Flow Measurements

Abstract. Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/). We harmonised and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well-represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks and remote sensing products to help increase our understanding of plant water use, plant responses to drought and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository ( https://doi.org/10.5281/zenodo.3971689, Poyatos et al., 2020a). The sapfluxnetr R package, designed to access, visualise and process SAPFLUXNET data is available from CRAN.

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Global transpiration data from sap flow measurements: the SAPFLUXNET database

Earth System Science Data ◽

10.5194/essd-13-2607-2021 ◽

2021 ◽

Vol 13 (6) ◽

pp. 2607-2649

Author(s):

Rafael Poyatos ◽

Víctor Granda ◽

Víctor Flo ◽

Mark A. Adams ◽

Balázs Adorján ◽

...

Keyword(s):

Time Series ◽

Sap Flow ◽

Structural Characteristics ◽

Vapour Pressure Deficit ◽

Environmental Drivers ◽

Plant Responses ◽

Flow Measurements ◽

Automatic Data ◽

Plant Transpiration ◽

Sap Flow Measurements

Abstract. Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The “sapfluxnetr” R package – designed to access, visualize, and process SAPFLUXNET data – is available from CRAN.

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Exploring Environmental Factors That Drive Diel Variations in Tree Water Storage Using Wavelet Analysis

Frontiers in Water ◽

10.3389/frwa.2021.682285 ◽

2021 ◽

Vol 3 ◽

Author(s):

Ryan E. Harmon ◽

Holly R. Barnard ◽

Frederick D. Day-Lewis ◽

Deqiang Mao ◽

Kamini Singha

Keyword(s):

Electrical Conductivity ◽

Wavelet Analysis ◽

Ponderosa Pine ◽

Water Storage ◽

Time Lapse ◽

Time Lags ◽

Storm Events ◽

Trunk Diameter ◽

Xylem Fluid ◽

Internal Water

Internal water storage within trees can be a critical reservoir that helps trees overcome both short- and long-duration environmental stresses. We monitored changes in internal tree water storage in a ponderosa pine on daily and seasonal scales using moisture probes, a dendrometer, and time-lapse electrical resistivity imaging (ERI). These data were used to investigate how patterns of in-tree water storage are affected by changes in sapflow rates, soil moisture, and meteorologic factors such as vapor pressure deficit. Measurements of xylem fluid electrical conductivity were constant in the early growing season while inverted sapwood electrical conductivity steadily increased, suggesting that increases in sapwood electrical conductivity did not result from an increase in xylem fluid electrical conductivity. Seasonal increases in stem electrical conductivity corresponded with seasonal increases in trunk diameter, suggesting that increased electrical conductivity may result from new growth. On the daily scale, changes in inverted sapwood electrical conductivity correspond to changes in sapwood moisture. Wavelet analyses indicated that lag times between inverted electrical conductivity and sapflow increased after storm events, suggesting that as soils wetted, reliance on internal water storage decreased, as did the time required to refill daily deficits in internal water storage. We found short time lags between sapflow and inverted electrical conductivity with dry conditions, when ponderosa pine are known to reduce stomatal conductance to avoid xylem cavitation. A decrease in diel amplitudes of inverted sapwood electrical conductivity during dry periods suggest that the ponderosa pine relied on internal water storage to supplement transpiration demands, but as drought conditions progressed, tree water storage contributions to transpiration decreased. Time-lapse ERI- and wavelet-analysis results highlight the important role internal tree water storage plays in supporting transpiration throughout a day and during periods of declining subsurface moisture.

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