scholarly journals Mechanisms linking plant productivity and water status for a temperate Eucalyptus forest flux site: analysis over wet and dry years with a simple model

2008 ◽  
Vol 35 (6) ◽  
pp. 493 ◽  
Author(s):  
David A. Pepper ◽  
Ross E. McMurtrie ◽  
Belinda E. Medlyn ◽  
Heather Keith ◽  
Derek Eamus
Keyword(s):  
Soil Moisture ◽  
Water Availability ◽  
Vapour Pressure ◽  
Water Status ◽  
Vapour Pressure Deficit ◽  
Co2 Flux ◽  
Lower Sensitivity ◽  
Forest Site ◽  
Eucalyptus Forest ◽  
Dry Conditions

A simple process-based model was applied to a tall Eucalyptus forest site over consecutive wet and dry years to examine the importance of different mechanisms linking productivity and water availability. Measured soil moisture, gas flux (CO2, H2O) and meteorological records for the site were used. Similar levels of simulated H2O flux in ‘wet’ and ‘dry’ years were achieved when water availability was not confined to the first 1.20 m of the soil profile, but was allowed to exceed it. Although the simulated effects of low soil and atmospheric water content on CO2 flux, presumably via reduction in stomatal aperture, also acted on transpiration, they were offset in the dry year by a higher vapour-pressure deficit. A sensitivity analysis identified the processes that were important in wet versus dry years, and on an intra-annual timeframe. Light-limited productivity dominated in both years, except for the driest period in the dry year. Vapour-pressure deficit affected productivity across more of each year than soil moisture, but both effects were larger in the dry year. The introduction of a reduced leaf area tended to decrease sensitivity in the dry year. Plant hydraulic architecture that increases plant available water, maximises productivity per unit water use and achieves lower sensitivity to low soil moisture levels should minimise production losses during dry conditions.

Seasonal changes in the water status of three woody legumes from the Atlantic forest, Caratinga, Brazil

2000 ◽  
Vol 16 (1) ◽  
pp. 21-32 ◽  
Author(s):  
J. P. Lemos Filho ◽  
C. V. Mendonça Filho
Keyword(s):  
Atlantic Forest ◽  
Vapour Pressure ◽  
Seasonal Changes ◽  
Water Status ◽  
Linear Equations ◽  
Canopy Cover ◽  
Correlation Coefficients ◽  
Vapour Pressure Deficit ◽  
Strong Relationship ◽  
Woody Legumes

The Atlantic forest of Brazil is considered to be a high priority for conservation in South America. Despite its importance, few phenological and ecophysiological data are available for plants of this area. In this study the seasonal changes in the water potentials (Ψ) and the phenological behaviour of three woody legumes are related to environmental conditions, particularly air vapour pressure deficit (VPD). The values of Ψ at predawn were greater than −0.75 MPa for all species even during the dry season (May–September). The minimal daily value of Ψ was −3.8 MPa. The maximum daily amplitude of Ψ (Δ parameter) was correlated with the air vapour pressure deficit, showing high correlation coefficients in linear equations. A high recovery rate of Ψ after rain (greater than 0.80) was registered for all species, suggesting a high hydraulic conductivity. The high values of Ψ at predawn during the year and the strong relationship between the daily amplitude of Ψ and VPD suggested that the changes in the canopy cover are related more to atmospheric drought than to soil water deficit.

An assessment of potato sap flow as affected by soil water status, solar radiation and vapour pressure deficit

1999 ◽  
Vol 79 (2) ◽  
pp. 245-253 ◽  
Author(s):  
R. Gordon ◽  
D. M. Brown ◽  
A. Madani ◽  
M. A. Dixon
Keyword(s):  
Soil Water ◽  
Water Use ◽  
Vapour Pressure ◽  
Sap Flow ◽  
Water Status ◽  
Vapour Pressure Deficit ◽  
Potato Cultivars ◽  
Rapid Decline ◽  
Plant Variation ◽  
Flow Monitoring

Water-use of three field-grown potato cultivars (Atlantic, Monona and Norchip) was examined using a commercially available sap flow monitoring system over three consecutive growing seasons. The objectives of the investigation were to utilize the sap flow system to assess the water use of three field-grown potato cultivars. This included an assessment of the relationship between environmental conditions, water status and measured sap flow including the plant-to-plant variation in sap flow and an evaluation of relative transpiration in relation to the soil water status.Each cultivar maintained daily sap flow close to the atmospheric potential transpiration until approximately 70% of the available water was depleted. Under conditions where the soil was drier (>70% depleted), Monona potato plants exhibited a more rapid decline in transpiration than Norchip and Atlantic.Hourly sap flow rates were closely related to solar irradiance, especially under well-watered conditions, with no apparent light saturation point. Vapour pressure deficit effects on sap flow were less pronounced, although maximum vapour pressure deficits encountered were only 2 kPa. Key words: Water use, sap flow, transpiration, potato

Sensitivity of evapotranspiration and surface conductance to vapour pressure deficit across high latitude climatic gradients.

2021 ◽  
Author(s):  
Astrid Vatne ◽  
Lena M. Tallaksen ◽  
Norbert Pirk ◽  
Ane V. Vollsnes ◽  
Kolbjørn Engeland ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
High Latitude ◽  
Vapour Pressure ◽  
Vapour Pressure Deficit ◽  
Surface Characteristic ◽  
Lower Latitude ◽  
Surface Conductance ◽  
Lower Sensitivity ◽  
Boundary Line ◽  
Area Index

<p>Evapotranspiration links the energy, water and carbon budgets of wetlands, a key ecosystem in high latitudes. While the evapotranspiration in high latitude wetlands is largely controlled by available energy, the surface also exerts a non-negligible control. The surface control on evapotranspiration, often represented by the surface conductance, is sensitive to environmental variables such as vapour pressure deficit (VPD). Previous studies have shown that higher surface conductance leads to higher evapotranspiration from high latitude wetlands than from high latitude forests during periods of high VDP. However, it is unclear how the surface conductance-VPD relation varies across climatic gradients. To study the sensitivity of surface conductance to increasing values of VPD, we use data from three recently established eddy covariance sites in Norway, situated along high latitude climatic gradients. The sites included are Hisåsen (680 m.a.s.l., N 61.11°, E 12.24°), Finse (1200 m.a.s.l., N 60.59°, E 7.53°) and Iškoras (360 m.a.s.l, N 69.34°, E 25.29°). We first estimate surface conductance from the eddy covariance data, by inverting the Penman-Monteith equation. We then apply a boundary line analysis to assess the sensitivity of the surface conductance to VPD. Our preliminary results show a lower sensitivity of surface conductance to VPD on the northernmost site, compared to the two sites at lower latitude. Further work is needed to relate the observed variations in surface conductance-VPD relation to surface characteristic, and we hypothesize that the observered lower sensitivity in surface conductance is related to lower values of leaf area index. This work is a contribution to the Strategic Research Initiative ‘Land Atmosphere Interaction in Cold Environments’ (LATICE) of the University of Oslo.</p>

Disentangling the relative contributions of atmospheric demand for water and soil water availability on the stomatal limitation of photosynthesis

2020 ◽  
Author(s):  
Aliénor Lavergne ◽  
Heather Graven ◽  
Iain Colin Prentice
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Water Availability ◽  
Optimality Theory ◽  
Stable Carbon Isotopes ◽  
Environmental Changes ◽  
Vapour Pressure Deficit ◽  
Soil Water Availability ◽  
Evaporative Demand ◽  
Spatial And Temporal Scales

<p>Plants open and close their stomata in response to changes in the environment, so they can absorb the CO<sub>2</sub> they need to grow, while also avoid drying out. Since the activities of leaf stomata determine the exchanges of carbon and water between the vegetation and the atmosphere, it is crucial to incorporate their responses to environmental pressure into the vegetation models predicting carbon and water fluxes on broad spatial and temporal scales. The least-cost optimality theory proposes a simple way to predict leaf behaviour, in particular changes in the ratio of leaf internal (<em>c</em><sub>i</sub>) to ambient (<em>c</em><sub>a</sub>) partial pressure of CO<sub>2</sub>, from four environmental variables, i.e. <em>c</em><sub>a</sub>, growing-season temperature (<em>T</em><sub>g</sub>), atmospheric vapour pressure deficit (<em>D</em><sub>g</sub>), and atmospheric pressure (as indexed by elevation, <em>z</em>). However, even though the theory considers the effect of atmospheric demand for water on <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub>, it does not predict how dry soils with reduced soil water availability further influence <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub>. Recent research has shown that independent of the individual effects of <em>T</em><sub>g</sub>, <em>D</em><sub>g</sub>, <em>c</em><sub>a</sub> and <em>z</em> on <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub>, the model tends to underestimate <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub> values at high soil moisture and to overestimate <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub> values at low soil moisture. Here, we will try to disentangle the relative contribution of <em>D</em><sub>g</sub> and soil moisture on changes in <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub> and test a new implementation of soil moisture effect in the framework of the least-cost hypothesis. To achieve this goal, we will use stable carbon isotopes measurements in leaves and in tree rings at sites with different soil water availability and different evaporative demand. We will then incorporate the improved model based on the least-cost hypothesis into the UK vegetation model JULES and investigate leaf stomatal responses to recent environmental changes across regions.</p>

scholarly journals Modeling transient soil moisture limitations on microbial carbon respiration

2018 ◽  
Author(s):  
Yuchen Liu ◽  
Matthew J. Winnick ◽  
Hsiao-Tieh Hsu ◽  
Corey R. Lawrence ◽  
Kate Maher ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Soil Column ◽  
Co2 Flux ◽  
Information Criterion ◽  
Order Model ◽  
First Order ◽  
Transition Mechanism ◽  
Dry Conditions ◽  
Shallow Soils ◽  
A Minor

Abstract. Observations show that soil microorganisms can survive periods of aridity and recover rapidly after wetting events. This behavior can be explained by a moisture-dependent adaptation (i.e. the ability to transition between a dormant state in dry conditions and an active state in wet conditions). Though this dynamic behavior has been previously incorporated into modeling frameworks, a direct comparison between a model application of this active-dormant transition mechanism and a more simplified first-order model has yet to be made. Here, we developed two models, one using simplified first-order kinetics and the other featuring a process-based rate expression incorporating the transition between active and dormant biomass. The two approaches are contrasted through a benchmarking exercise using a set of time series soil incubation datasets. We evaluated the two models using an Akaike Information Criterion (AIC). Combining the AIC evaluation and model-data comparison, we conclude that the dormancy-incorporated model performs better for shallow soils (above 108 cm), despite the added parameters required. In addition, this model is uniquely capable of reproducing transient CO2 flux rates associated with dynamic microbial response to changing soil moisture. In contrast, the first-order model achieves better AIC scores when simulating the incubation data obtained from our deepest soils (112–165 cm). However, deep soils constitute a minor contribution to the overall CO2 flux of an intact soil column. Thus, the dormancy-incorporated model may better simulate respiration of the whole soil.

Complex edge effects on soil moisture and microclimate in central Amazonian forest

1995 ◽  
Vol 11 (2) ◽  
pp. 205-221 ◽  
Author(s):  
J. L. C. Camargo ◽  
V. Kapos
Keyword(s):  
Soil Moisture ◽  
Edge Effects ◽  
Vegetation Structure ◽  
Vapour Pressure ◽  
Vapour Pressure Deficit ◽  
Forest Edge ◽  
Vertical Profiles ◽  
Control Soil ◽  
Neutron Probe ◽  
Microclimatic Conditions

ABSTRACTWe investigated the influence of a four-year-old forest edge near Manaus, Brazil, on soil moisture and vertical profiles of air vapour pressure deficit (VPD) within the forest. Soil moisture was measured (with a neutron probe) 0, 5, 10, 20, 40, 60, 80, 100, 150 and 200 m into the forest from the edge, in undisturbed control areas, and in the pasture. Control soil moisture was better explained by rainfall in the previous 2 or 10 days than by longer-term totals. Soil water potentials ≤ – 1.5 MPa occurred at some forest locations during the driest period. The variation in soil moisture with distance from the forest edge was complex, with higher values just inside the edge and depleted zones at the edge and 40–80 m inside it. At a given height, VPD (standardized relative to measurements in the open) was not related to distance from the edge, but VPD increased more with height near the edge than in control areas. The complexity of the edge's influence and the contrast with earlier data from the same edge can be explained by the changing vegetation structure near the edge. Regrowth ‘seals’ the edge with more leaves that transpire and deplete soil moisture, while protecting the understorey just inside the edge from desiccating conditions. A mosaic of gaps of differing ages develops behind the edge, increasing the variation in microclimatic conditions near the ground and consequently in evapotranspiration and soil moisture.

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