Canopy Gas Exchange and Water Use Efficiency of ‘Empire’ Apple in Response to Particle Film, Irrigation, and Microclimatic Factors
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This study examined the interaction between a reflective particle film and water use efficiency (WUE) response of irrigated and non-irrigated apple trees ( Malus × domestica ) over a wide range of environmental conditions. The objectives were to measure isotopic discrimination (Δ 13 C and δ 18 O), specific gas exchange, and WUE response of ‘Empire’ apple treated with a reflective particle film (PF), with and without supplemental irrigation, compared with an untreated control, with and without supplemental irrigation, over a range of leaf area indices (LAI), seasonal evapotranspiration (ETo), and vapor pressure deficits (VPD) to determine the mechanisms of action affecting WUE in apple. Short-term whole canopy gas exchange studies and isotope discrimination analysis were used to test the hypothesis that WUE was modified by the use of a PF. In whole canopy gas exchange studies, carbon assimilation (A) and transpiration tended to increase, and WUE and canopy conductance tended to decrease, with VPD within each LAI class from 2 to 6. For VPD > 1 kPa, the PF irrigated treatment consistently had the greatest WUE and other treatments were intermediate for LAI of 2 to 4. The PF irrigated and non-irrigated treatments had greater WUE than the control irrigated and non-irrigated treatments for VPD ≤ 2 kPa and there were no treatment effects for VPD > 2 kPa in the LAI range of 4 to 6. The PF non-irrigated was equivalent to the control non-irrigated treatment at VPD of 1 to 3 kPa, but was significantly lower at VPD of 3 to 4 kPa. PF irrigated and non-irrigated treatments had the greatest carbon isotope discrimination (Δ 13 C), the control non-irrigated treatment had the lowest Δ 13 C, and the control-irrigated treatment was intermediate. Oxygen isotope enrichment (δ 18 O) was positively correlated with the mean growing season VPD and mean growing season evapotranspiration. Δ 13 C was significantly and positively correlated with δ 18 O. Seasonal WUE was negatively correlated with Δ 13 C and there was an interaction with LAI. The seasonal water use of apple is better evaluated with stable isotope discrimination integrating seasonal variation rather that the use of whole canopy gas exchange measurements that measure WUE for brief periods of time. Δ 13 C was an accurate measurement of apple WUE and indicated that the PF irrigated treatment had the greatest Δ 13 C and so the lowest WUE compared with the control non-irrigated treatment at LAI from 4 to 6. The reduced WUE of the PF irrigated treatment compared with the control non-irrigated treatment is likely due to increased g S from lower canopy temperature and increased canopy photosynthetically active radiation diffusion that drove increased A. δ 18 O was an indicator of seasonal water use over six growing seasons due to its high correlation with ETo. In ‘Empire’ apple, A can be increased with PF and irrigation treatments, but at the cost of decreased WUE.Keywords:
Water Use Efficiency
Canopy conductance
Stomatal Conductance
Malus
This study examined the interaction between a reflective particle film and water use efficiency (WUE) response of irrigated and non-irrigated apple trees ( Malus × domestica ) over a wide range of environmental conditions. The objectives were to measure isotopic discrimination (Δ 13 C and δ 18 O), specific gas exchange, and WUE response of ‘Empire’ apple treated with a reflective particle film (PF), with and without supplemental irrigation, compared with an untreated control, with and without supplemental irrigation, over a range of leaf area indices (LAI), seasonal evapotranspiration (ETo), and vapor pressure deficits (VPD) to determine the mechanisms of action affecting WUE in apple. Short-term whole canopy gas exchange studies and isotope discrimination analysis were used to test the hypothesis that WUE was modified by the use of a PF. In whole canopy gas exchange studies, carbon assimilation (A) and transpiration tended to increase, and WUE and canopy conductance tended to decrease, with VPD within each LAI class from 2 to 6. For VPD > 1 kPa, the PF irrigated treatment consistently had the greatest WUE and other treatments were intermediate for LAI of 2 to 4. The PF irrigated and non-irrigated treatments had greater WUE than the control irrigated and non-irrigated treatments for VPD ≤ 2 kPa and there were no treatment effects for VPD > 2 kPa in the LAI range of 4 to 6. The PF non-irrigated was equivalent to the control non-irrigated treatment at VPD of 1 to 3 kPa, but was significantly lower at VPD of 3 to 4 kPa. PF irrigated and non-irrigated treatments had the greatest carbon isotope discrimination (Δ 13 C), the control non-irrigated treatment had the lowest Δ 13 C, and the control-irrigated treatment was intermediate. Oxygen isotope enrichment (δ 18 O) was positively correlated with the mean growing season VPD and mean growing season evapotranspiration. Δ 13 C was significantly and positively correlated with δ 18 O. Seasonal WUE was negatively correlated with Δ 13 C and there was an interaction with LAI. The seasonal water use of apple is better evaluated with stable isotope discrimination integrating seasonal variation rather that the use of whole canopy gas exchange measurements that measure WUE for brief periods of time. Δ 13 C was an accurate measurement of apple WUE and indicated that the PF irrigated treatment had the greatest Δ 13 C and so the lowest WUE compared with the control non-irrigated treatment at LAI from 4 to 6. The reduced WUE of the PF irrigated treatment compared with the control non-irrigated treatment is likely due to increased g S from lower canopy temperature and increased canopy photosynthetically active radiation diffusion that drove increased A. δ 18 O was an indicator of seasonal water use over six growing seasons due to its high correlation with ETo. In ‘Empire’ apple, A can be increased with PF and irrigation treatments, but at the cost of decreased WUE.
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Canopy conductance
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Malus
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Stomatal Conductance
Canopy conductance
Water Use Efficiency
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Canopy conductance
Stomatal Conductance
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Stomatal Conductance
Canopy conductance
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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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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) .
Stomatal Conductance
Photosynthetically active radiation
Canopy conductance
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Stomatal Conductance
Photosynthetically active radiation
Canopy conductance
Biometeorology
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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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