Estimating Bulk Stomatal Conductance in Grapevine Canopies
Mark GowdyPhilippe PieriBruno SuterElisa MargueritAgnès Destrac-IrvineGregory A. GambettaCornelis van Leeuwen
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Abstract:
In response to changes in their environments, grapevines regulate transpiration using various physiological mechanisms that alter conductance of water through the soil-plant-atmosphere continuum. Expressed as bulk stomatal conductance at the canopy scale, it varies diurnally in response to changes in vapor pressure deficit and net radiation, and over the season to changes in soil water deficits and hydraulic conductivity of both the soil and plant. To help with future characterization of this dynamic response, a simplified method is presented for determining bulk stomatal conductance based on the crop canopy energy flux model by Shuttleworth and Wallace using measurements of individual vine sap flow, temperature and humidity within the vine canopy, and estimates of net radiation absorbed by the vine canopy. The methodology presented respects the energy flux dynamics of vineyards with open canopies, while avoiding problematic measurements of soil heat flux and boundary layer conductance needed by other methods, which might otherwise interfere with ongoing vineyard management practices. Based on this method and measurements taken on several vines in a non-irrigated vineyard in Bordeaux France, bulk stomatal conductance was estimated on 15-minute intervals from July to mid-September 2020 producing values similar to those presented for vineyards in the literature. Time-series plots of this conductance show significant diurnal variation and seasonal decreases in conductance associated with increased vine water stress as measured by predawn leaf water potential. Global sensitivity analysis using non-parametric regression found transpiration flux and vapor pressure deficit to be the most important input variables to the calculation of bulk stomatal conductance, with absorbed net radiation and bulk boundary layer conductance being much less important. Conversely, bulk stomatal conductance was one of the most important inputs when calculating vine transpiration, emphasizing the usefulness of characterizing its dynamic response for the purpose of estimating vine canopy transpiration in water use models.Keywords:
Stomatal Conductance
Vineyard
Canopy conductance
Stomatal Conductance
Canopy conductance
Water Use Efficiency
Biometeorology
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Corylus avellana L. is a species highly susceptible to water stresses caused by vapor pressure deficit and high temperature. Under such conditions, transpiration is strongly constrained even with good soil water availability. This is due to ineffective drought resistance mechanisms and indicates the need to identify early indicators of plant stress that are easy to measure, effective and efficient. This research explored the possibility of using stomatal conductance and leaf water potentials as early indicators of stress. For this purpose, an experiment was set up in a commercial 5-year-old Corylus avellana L. var. 'McDonald' orchard located in Willamette valley. The experimental designed featured irrigated and rainfed trees, and potential stress indicators were monitored at different times of the day in canopy sections aligned to cardinal directions. Results show that hazelnut trees rapidly reduced leaf stomatal conductance when the vapor pressure deficit increased to 2 and 2.5 kPa during the diurnal cycle in both irrigated and rainfed trees, even with good water availability. This suggests leaf stomatal conductance can be an efficient and effective early indicator of stress. In addition, results suggest that stomatal conductance should be measured on leaves on the west and north aspects of the canopy, where they showed lowest and highest values respectively. Leaf and stem water potential values increased during the measurement period and show a strong correlation, but their mean values do not show statistically significant differences between treatments. In Willamette valley conditions, stomatal conductance provided earlier indication of stress than water potential. The results obtained are of methodological importance for the future design of experimental plans.
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In response to changes in their environments, grapevines regulate transpiration using various physiological mechanisms that alter conductance of water through the soil-plant-atmosphere continuum. Expressed as bulk stomatal conductance at the canopy scale, it varies diurnally in response to changes in vapor pressure deficit and net radiation, and over the season to changes in soil water deficits and hydraulic conductivity of both the soil and plant. To help with future characterization of this dynamic response, a simplified method is presented for determining bulk stomatal conductance based on the crop canopy energy flux model by Shuttleworth and Wallace using measurements of individual vine sap flow, temperature and humidity within the vine canopy, and estimates of net radiation absorbed by the vine canopy. The methodology presented respects the energy flux dynamics of vineyards with open canopies, while avoiding problematic measurements of soil heat flux and boundary layer conductance needed by other methods, which might otherwise interfere with ongoing vineyard management practices. Based on this method and measurements taken on several vines in a non-irrigated vineyard in Bordeaux France, bulk stomatal conductance was estimated on 15-minute intervals from July to mid-September 2020 producing values similar to those presented for vineyards in the literature. Time-series plots of this conductance show significant diurnal variation and seasonal decreases in conductance associated with increased vine water stress as measured by predawn leaf water potential. Global sensitivity analysis using non-parametric regression found transpiration flux and vapor pressure deficit to be the most important input variables to the calculation of bulk stomatal conductance, with absorbed net radiation and bulk boundary layer conductance being much less important. Conversely, bulk stomatal conductance was one of the most important inputs when calculating vine transpiration, emphasizing the usefulness of characterizing its dynamic response for the purpose of estimating vine canopy transpiration in water use models.
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AbstractCyperus papyrus forms highly productive wetlands in tropical Africa, but the environmental control of transpirational water loss in wetlands is poorly understood. The influence of climate variables on papyrus stomatal conductance in dry and wet seasons of the year was investigated in a wetland in Kampala, Uganda, in June–December, 2012. In situ measurements were made of local climate conditions in a papyrus canopy and of bracteole stomatal conductance. Stomatal conductance was highest early in the day and declined as the day progressed, but stomata were more consistently open in the wet season than in the dry season. The daily cycle of stomatal conductance was influenced by temperature, incident radiation and vapour pressure deficit. Stomata were more sensitive to vapour pressure deficit changes during the wet season than in the dry season, closing sharply as vapour pressure deficit increased. This would seem to be a useful strategy for regulating transpiration, as it reduces water loss when the vapour pressure deficit gradient between the leaf intercellular spaces and the atmosphere is greatest.Keywords: acclimatisationphotosynthetically active radiationrelative humiditytemperaturevapour pressure deficit
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Stomatal behavior under global climate change is a central topic of plant ecophysiological research. Vapor pressure deficit (VPD) and phytohormones can affect stomata of leaves which can affect gas exchange characteristics of plant. The role of VPD in regulating leaf gas exchange of three tree species was investigated in Jinan, China. Experiments were performed in June, August, and October. Levels of three phytohormones (GA3, IAA, ABA) in the leaves of the three trees were determined by high-performance liquid chromatography in three seasons. The responses of stomatal conductance (gs) to an increasing VPD in the leaves of the three trees had peak curves under different seasons, which differed from the prevailing response pattern of gs to VPD in most literature. The peak curve could be fitted with a Log-Normal Model (R2 = 0.838-0.995). The VPD/RH values of the corresponding maximum of gs (gs-max-VPD/RH) could be calculated by fitted models. The gs-max-RH could be affected by environmental conditions, because of positive correlation between gs-max-RH and the mean monthly temperature in 2010 (R2 > 0.81). Two typical stomatal models (the Leuning model and the optimal stomatal behavior model) were used to estimate gs values, but they poorly predicted gs in the three trees. The concentration of ABA was positively correlated to sensitivity in response of stomatal conductance to VPD in the leaves of the tree species during the different seasons.
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Detailed measurements of leaf stomatal conductance and photosynthesis of Aneurolepidium chinense were used to analyze the relationship between stomatal conductance and environmental factors and to develop a leaf stomatal conductance model for A. chinense . The results show that leaf stomatal conductance of A. chinense is sensitive to photosynthetically active radiation ( PAR) , vapor pressure deficit ( VPD ) and air temperature ( Ta ). Stomatal conductance increased with increasing PAR and Ta and decreased with increasing VPD . Validations of Jarvis' and Ball's models based on field data of leaf stomatal conductance in A. chinense indicate that model is a better estimate of g s than Ball's. The relationship between leaf stomatal conductance( g s) and environmental factors could be expressed as:g s = PAR (-2.01Ta 2+147.74Ta-2321.11)/((444.62+PAR)(-538.04+VPD))This model will be very helpful to simulate the dynamic photosynthesis at both leaf and canopy scales and also to simulate the NPP of ecosystems and energy and water balances in the Soil Plant Atmosphere Continum (SPAC) .
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Based on the diurnal change of stomatal conductance (Gs) of ginseng under forest, the qualities of the environmental factors to Gs were confirmed with correlation analysis. The interaction among factors was analysed with the method of multiple regression analysis. A conclusion was the main factors impacting on stomatal conductance (Gs) of ginseng under forest were photosynthetically active radiation (PAR), air temperature (Ta) and vapor pressure deficit (VPD). The relationship between stomatal conductance (Gs) of the leaf and environmental factors could be expressed as:Gs=4.712PAR×10-4+1.559Ta×10-2-0.002VPD-3.657,(R=0.971**,F=59.074).
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Jarvis-type model with a flexible parameterization of stress functions can improve the descriptions of physiological behaviour for specific vegetation species. However, it is criticized for the empirically formulated multiplicative equation that can deviate from the mutual impact of intercorrelated stress factors, e.g., vapor pressure deficit (VPD) and air temperature ( T ). This study proposed a modified Jarvis model by adding reduction factors in the stress functions of VPD and T to provide a better description of stomatal conductance. The sap flow data of transpiration rate in a beech forest in the mid-latitude of Centre Europe was used to inversely estimate the stomatal conductance, which facilitated the formulation of stress functions. Taking two recommended parameterization strategies for general deciduous broadleaf forest (DBF) led to severe overestimation of transpiration rate with a maximum value of ~2 mm/day in rainless days, which suggested that the beech forest had rather different stomatal response. With the parameterization using boundary analysis, the unmodified and modified Jarvis model provided the better simulation of transpiration with NSE values of 0.75 and 0.77. The results suggested that modelling transpiration can be improved through a more specific parameterization of stomatal conductance, especially for a vegetation species featuring its own stomatal behaviour that differed from its belonged general vegetation type. Particularly, the modified Jarvis model can further improve the description of stomatal conductance and modelling of transpiration in vegetated areas, especially under dry environment conditions with relatively high VPD.
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