Effect of highly processed calcined kaolin residues on apple water use efficiency

Scientia Horticulturae 205 (2016) 127–132

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Effect of highly processed calcined kaolin residues on apple water use efficiency夽 D.M. Glenn USDA-ARS-Appalachian Fruit Research Station, Kearneysville, WV 25430, United States

a r t i c l e

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Article history: Received 11 February 2016 Received in revised form 18 April 2016 Accepted 20 April 2016 Available online 28 April 2016 Keywords: Malus x domestica Carbon isotopic discrimination Photosynthesis Transpiration Fruit yield Biomass Evapotranspiration Gas exchange Radiation use efficiency

a b s t r a c t Processed calcined kaolin particle films (PKPF) have been shown to repel some insects and reduce various environmental stresses often resulting in improved yield and quality of horticultural crops. PKPF studies in the literature have various water use efficiency (WUE) responses. The purpose of this study was to evaluate 2 application rates of PKPF (3% and 12%) on the whole tree water use efficiency and compare gas exchange values with carbon isotopic discrimination and seasonal water use efficiency in order to determine if there are consistent effects on WUE in apple and infer the mechanisms of action. Fruit yield and total biomass influence WUE whether WUE is measured directly in whole plant chambers, estimated by biomass/unit evapotranspiration, or 13 C. 13 C analysis of WUE generally found that the untreated control had lower values and therefore higher WUE than PKPF treatments. Whole plant gas exchange analysis of WUE generally lacked the sensitivity to identify the treatment differences observed using 13 C analysis and those treatment differences identified were contrary to 13 C analysis. A lysimeter study supported the reduced WUE of PKPF treated plants by demonstrating increased E with a range of PKPF residue amounts. The lysimeter results suggest that for well-watered and presumably non-stressed conditions, gas exchange is limited by leaf temperature and the concomitant leaf-air vapor pressure deficit that influence stomatal conductance. When leaf temperature is reduced by PKPF, the response results in increased stomatal conductance and gas exchange, as measured by increased E. The reduction in WUE by PKPF treatment is balanced by an increase in overall gas exchange and increased yield and quality. Published by Elsevier B.V.

1. Introduction Processed calcined kaolin particle films (PKPF) reduced insect, heat, photosynthetically active radiation (PAR) and ultraviolet radiation (UV) stress in plants due to the reflective nature of the particles (Glenn and Puterka, 2005). In addition PKPF increased the microbial biomass on the leaf surface (Glenn et al., 2015) and together the particles and microbial biomass may aid in the mitigation of ozone damage (Glenn, 2016). The particle film alters reflected infrared (IR), PAR, and UV radiation compared to an untreated plant (Glenn et al., 2002; Glenn, 2016) resulting in reduced canopy temperatures and increased intra-canopy PAR (Glenn and Puterka, 2007; Rosati et al., 2006, 2007; Wünsche et al.,

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2004) which has improved fruit color and mass (Glenn and Puterka, 2007; Glenn 2016). Reduced canopy temperature can potentially reduce transpiration (Boari et al., 2015; Glenn, 2010; Jifon and Syvertsen, 2003; Moftah and Al-Humaid, 2005; Steiman et al., 2011) which may alter water use efficiency (WUE). Studies of leaf-level water use efficiency (WUEleaf ) in different crops demonstrate that PKPF can increase (Tworkoski et al., 2002; Jifon and Syvertsen, 2003; Moftah and Al-Humaid, 2005; Boari et al., 2014; Cantore et al., 2009; Prive et al., 2006; Boari et al., 2015), have no effect (Denaxa et al., 2012; Roussos et al., 2010; Gindaba and Wand, 2007a,b; Glenn et al., 2010; Prive et al., 2007; Steiman and Bittenbender, 2007) or decrease (Le Grange et al., 2002) WUE. There are fewer whole canopy and carbon isotopic discrimination studies evaluating PKPF effects on WUE and those demonstrate both increased (Cantore et al., 2009; Glenn et al., 2010), no effect (Lombardini et al., 2005; Steiman and Bittenbender, 2007) and decreased (Glenn 2010; Glenn et al., 2003) WUE. The reflection of PAR by the particle film at the leaf level is compensated in varying degrees by diffusion of PAR into the interior of the canopy. The combined particle film effects of reduced canopy

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temperature and increased diffusion of PAR into the interior of the canopy can increase whole canopy photosynthesis (Glenn et al., 2003; Glenn, 2009, 2010) or have no effect (Wünsche et al., 2004). The effect of PKPF on yield studies is similarly inconsistent. Excluding sunburn effects, many studies show increased yield and fruit quality of horticultural crops (Aly et al., 2010; Glenn, 2009, 2010; Glenn and Puterka, 2007; Glenn et al., 2001, 2003, 2005; Lapointe et al., 2006; Cantore et al., 2009; Pace et al., 2007; Wand et al., 2006; Saavedra et al., 2006; Steiman and Bittenbender, 2007; Boari et al., 2014; Ergun, 2012; Khaleghi et al., 2015; Lalancette et al., 2005; Shellie and Glenn, 2008; Shellie and King, 2013; Sugar et al., 2005). There are also studies demonstrating no or negative effects of PKPF on fruit yield and quality (Schupp et al., 2002; Gindaba and Wand, 2005; Kahn and Damicone 2008; Lombardini et al., 2005; Russo and Diaz-Perez, 2005). Based on the methods of these studies it is most likely that the particle films had a residue density of 1–4 g m−2 based on application rates ranging from 12 to 50 kg/ha. The purpose of this study was to evaluate 2 application rates of PKPF (3% and 12%) on the whole tree water use efficiency and compare gas exchange values with carbon isotopic discrimination and seasonal water use efficiency in order to determine if there are consistent effects on WUE in apple and infer the mechanisms of action. 2. Methods and materials 2.1. Field plots and treatment application The apple orchard was a moderate density planting (500 ha−1 ) of ‘Empire’/‘Malling7A’ planted in 1992 at the USDA/ARS Appalachian Fruit Research Station, Kearneysville, WV. Tree water requirements were based on 70% of pan evaporation (Glenn, 1995, 1999). Irrigation treatments consisted of two drip emitters per tree providing the daily water needs. Treatments were randomly assigned in 2005 in a split-plot block design with irrigation as the main plot and PKPF treatment as the subplot with six, two tree replicates. In all years, the trees were hand-thinned post-bloom. Trees received a PKPF treatment (3% or 12%) or were not treated. All treatments were over-sprayed with conventional pesticides to protect from disease or insect damage. Conventional orchard practices were used in tree training, mowing, nutrition, and weed control. Apple trees received applications of a highly reflective, white, calcined hydrophilic particle based on the kaolin mineral (PKPF treatment was Surround WPTM , NovaSource, a division of Tessenderlo Kerley Inc. Phoenix, AZ) in addition to a conventional pesticide spray program. Surround WP was applied at the rate of 25 kg/ha and 100 kg/ha for 3% and 12% (w/v) during the 2005–2010 growing seasons. The Surround WP treatments were applied in a spray volume of 833 L ha−1 (approximately 50% of tree row volume) using an air blast sprayer at a ground speed of 3.2 km/h. There was an untreated control treatment. PKPF treatments were applied every 2 weeks following petal fall until 2–3 weeks before harvest. 2.2. Field measurements At harvest, all fruit were weighed and counted for each tree in a plot. Fruit from each tree were processed with an electronic grader that counted and weighed each fruit. Following harvest, the trees were covered with a netting to capture all the leaves when they abscised. The leaves were collected and air-dried at 60 ◦ C for approximately 1 week. At field sampling, a subsample of approximately 1 kg fresh weight was separated, leaf area was measured, and the ratio of air-dried weight:leaf area calculated. This ratio was used to convert the total air-dried weight of each tree to total leaf area. Pruning weights from each tree were collected in the dormant season and weighed. Mean fruit dry weight

(at 60 ◦ C) was 17% fresh weight and mean wood dry weight (at 60 ◦ C) was 40% pruning weight in the field. Biomass was the dry weight sum of leaf, fruit and dormant season pruning. Photosynthetically active radiation (PAR), relative humidity, wind speed, pan evaporation, and air temperature were measured at a weather station approximately 500 m from the measurement site. Pan evaporation was measured 3 times/week and the seasonal transpiration potential (Ef ) was calculated as 0.8 X seasonal cumulative pan evaporation. Radiation use efficiency for each year was calculated as biomass (kg/tree)/canopy area (m2 )/seasonal PAR interception (GJ).The growing season was May to September. Whole tree gas exchange was measured in open-top chambers similar to Glenn (2010). The whole canopy chamber was constructed of 0.762-mm-thick polycarbonate (Makrolon GP; Sheffield Plastics Inc.—Bayer Material Sciences Pittsburgh, PA) in a rigid cube 2.4 × 2.4 × 2.4 m. A framed polycarbonate pitched roof covered the cube and the floor was a polyethylene tarp material split to the center to slide onto the tree and was sealed with a Velcro strip. Details of the gas exchange chambers are described in Glenn (2010). Diurnal data were collected: 2005 DOY’s 202–226; 2006 DOY’s 217–225; 2007 DOY’s 255–263; 2008 DOY’s 238–244; 2009 DOY’s 225–239; 2010 DOY’s 241–242 and 264–266. During each sampling, eight trees, including two or three trees of each treatment, were simultaneously measured for multiple days. After sampling, the chambers were moved to eight other trees multiple times providing four single tree replications of each treatment for whole tree gas exchange. Data were collected for 24 h each day but only data from 1000 to 1600HR, were analyzed. PKPF treatment effects were analyzed over days and hours using analysis of covariance in which yield and biomass were the independent variables. Data were analyzed using SAS (version 8). Adjusted treatment means were compared using PDIFF which compares least squares means from the analysis of covariance. Treatment means were compared using Fisher’s protected least significant difference (LSD), P ≤ 0.05. Twenty mid-shoot leaves per tree were collected in late July to early August, washed with deionized water and air dried at 60◦ C for approximately one week. The tissue was re-dried at 60 ◦ C for 72 h, ground, and analyzed for 13 C content (University of California, Davis Stable Isotope Facility, Department of Plant Sciences, One Shields Ave, Mail Stop 1, Davis, CA 95616, USA). Carbon isotope discrimination (13 C) was calculated according to Farquhar et al. (1989). The carbon dioxide isotope composition in air (␦ 13 Cair ) was assumed to be −7.8 parts per thousand (Francey et al., 1995). 2.3. Lysimeter study 2015 Two weighing lysimeters (Cardinal Scale Co., Webb City, MO; model FS-8; see Glenn et al., 1996) were used to measure whole tree transpiration by measuring weight loss from 9 AM to 5 PM. Tenyear-old ‘Empire’ apple trees were transplanted to plastic apple bins (1.1 m × 1.1 m × 0.7 m; L × W × D) in 2008 and grown with supplemental irrigation and fertilization under field conditions. The apple containers were placed directly on the surface of the lysimeter; the surface of the lysimeter was covered with a waterproof covering. During the study, irrigation was applied at midnight and drainage was completed by sunrise. Baseline data from both untreated trees was measured DOY’s 186–193 and the tree to be treated had 70.12% of the mean E compared to the control tree. The treated tree E was normalized by dividing its E by 0.7012. Applications of Surround were applied with an orchard sprayer similar to the field studies although multiple applications were made to achieve greater and greater residue levels. The following residue amounts were measured: DOY’s 199–202, 0.5 g/m2 ; DOY’s 203–207, 1.3 g/m2 ; DOY’s 208–211, 2.8 g/m2 ; DOY’s 212–215, 4.9 g/m2 ; DOY’s 216–217, 3.95 g/m2 (reduced by rain); DOY’s 220–221, 15.8 g/m2 ; DOY’s 222–223, 7.0 g/m2 (reduced by rain);

D.M. Glenn / Scientia Horticulturae 205 (2016) 127–132

25 Isotopic carbon discriminaon ( 0/00)

Mean daily photosynthesis (umol/m2/s)

10

129

y = 0.6356x + 3.196 R² = 0.63

9 8 7 6 5 4 3

Control

2

3% PKPF

1

12% PKPF

3% and 12% PKPF y = -0.0725x + 22.361 R² = 0.35

20 15

Control y = -0.1125x + 22.501 R² = 0.52

10

Control 3% PKPF

5

12% PKPF

0 0

5

10

15

20

25

30

35

40

Biomass (kg/tree)

0 2

4 6 Mean daily transpiraon (mmol/m 2/s)

8

10

Fig. 1. Relationship between mean daily photosynthesis and transpiration for ‘Empire’ apple trees receiving 0%, 3% or 12% applications of PKPF for a 6 year period (2005–2010).

DOY’s 224–228, 28.3 g/m2 ; DOY’s 229–235, 0.1 g/m2 (trees were washed with detergent and rinsed to remove residue). Leaf residue amounts were measured on 5 leaves/tree. Pre-weighed tissue was wetted and used to wipe clean the leaf. The tissues were dried and re-weighed. The additional weight of the tissue was attributed to the PKPF residue, native dust and some leaf pubescence. Control leaves were measured to account for native dust and leaf pubescence removed in the wiping process. Leaf area of the 5 leaves for each treatment were measured and the g residue/m2 leaf area calculated. The PKPF residue amount was the treated minus control mean leaf residue (g/m2 ). At the end of the study, the treated tree was washed with detergent and rinsed to remove the residue. Five leaves were measured to determine the PKPF residue level after washing. Thermal infrared images of tree canopies on the lysimeters were made on two dates (August 4 and 5, 2015) approximately 1 h after solar noon using a model A40 FLIR thermal IR video imagery system (FLIR, Inc. Billerica, Mass.). Both trees were included in the field of view. FLIR Researcher software was used to calculate canopy surface temperature distribution. The amount of PKPF residue on the canopy was estimated as described previously. The thermal emissivity of the PKPF material was equivalent to plant tissue (data not presented) and 0.98 was used. 3. Results and discussion Irrigation had no significant effect on whole tree gas exchange so the data were pooled. There were no PKPF treatment differences in daily water use efficiency (WUEchamber ) (photosynthesis/transpiration) measured in gas exchange chambers (2005–2010) (Fig. 1). Studies of leaf-level water use efficiency (WUEleaf ) in different crops demonstrate that PKPF can increase (Tworkoski et al., 2002; Jifon and Syvertsen, 2003; Moftah and Al-Humaid, 2005; Boari et al., 2014; Cantore et al., 2009; Prive et al., 2006; Boari et al., 2015), have no effect (Denaxa et al., 2012; Roussos et al., 2010; Gindaba and Wand, 2007a,b; Glenn et al., 2010; Prive et al., 2007; Steiman and Bittenbender, 2007) or decrease (Le Grange et al., 2002) WUEleaf . Glenn (2010) and Glenn et al. (2003) measured reduced WUEchamber and found reduced WUEchamber using 3% PKPF. The biological basis for this variation may be associated with the yield level or overall dry matter partitioning of the plants. The present study found that WUEchamber was positively related to the fruit load of the tree (r = 0.57) and overall dry matter production (r = 0.60). PKPF studies have demonstrated increased yield (Aly et al., 2010; Glenn, 2009, 2010; Glenn and Puterka, 2007; Glenn et al., 2001, 2003, 2005; Lapointe et al., 2006;

25 Leaf Isotopic carbon discriminaon ( o/oo)

0

3% and 12% PKPF y = -44.184x + 22.307 R² = 0.34

20

15

10 Control Control y = -78.221x + 22.453 R² = 0.61

3% PKPF

5

12% PKPF 0 0

0.01

0.02

0.03

0.04

0.05

0.06

Biomass/ unit evapotranspiraon (kg/tree/mm) Fig. 2. Relationship between leaf 13 C isotopic discrimination (13 C) and biomass (top) or biomass/unit evapo-transpiration (bottom) for ‘Empire’ apple trees receiving 0%, 3% or 12% applications of PKPF for a 6 year period (2005–2010).

Cantore et al., 2009; Pace et al., 2007; Wand et al., 2006; Saavedra et al., 2006; Steiman and Bittenbender, 2007; Boari et al., 2014; Ergun, 2012; Khaleghi et al., 2015; Lalancette et al., 2005; Shellie and Glenn, 2008; Shellie and King, 2013; Sugar et al., 2005) and no or reduced yield effect (Schupp et al., 2002; Gindaba and Wand, 2005; Kahn and Damicone, 2008; Lombardini et al., 2005; Russo and Diaz-Perez, 2005) which would likely influence water use efficiency in those studies. Mean WUEchamber measured on a daily basis was positively correlated with the seasonal water use efficiency calculated as fruit mass (kg)/evapo-transpiration amount (mm) (r = 0.62) and biomass (kg)/evapo-transpiration amount (mm) (r = 0.58) confirming the dependency of WUE, however measured, to the dry matter and particularly the dry matter partitioned to fruit. In seasonal dry matter yield studies (Glenn, 2014), 13 C isotopic discrimination (13 C) responses of apple leaves were highly negatively correlated with WUE based on the annual fruit yield/seasonal potential transpiration (Ef ), termed WUEFrt as well as fruit yield and total biomass. In the present study, 13 C was negatively correlated with fruit yield (kg/tree) (r = −0.62) with no treatment differences, however, there were small but significantly different treatment effects in the relationship between 13 C and annual biomass production (Fig. 2 top). 3% and 12% PKPF had a less negative slope than the control indicating a decreased WUE since WUE is negatively proportional to 13 C. There were similar treatment differences for seasonal biomass water use efficiency (Fig. 2 bottom). There were no treatment effects for the WUEchamber relationship with 13 C and no significant correlation (data not presented). Analysis of covariance for WUEchamber using fruit yield or biomass as the covariate indicated that the 3% PKPF treatment had greater WUEchamber than the control or 12% PKPF (1.96 ␮mol/mol vs 1.63 and 1.51 ␮mol/mol, respectively) but control 13 C was lower than 12% PKPF and 3%

200

3% and 12% PKPF y = -0.0952x + 134.91 R² = 0.12

150 100 Control 3% PKPF 12% PKPF

50 0 0

50

50 100 150 Fruit yield (kg/tree)

200

1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0

y = 0.2035x + 6.278 R² = 0.89

40 30

20

30

Fig. 4. Relationship between normalized daily transpiration ([PKPF/0.701]/control) and the PKPF residue amount from lysimeter responses for ‘Empire’ apple from July through August 2015.

Control

20

10

Residue (g/m2)

3% PKPF 12% PKPF

10

22.5

0 0

50 100 150 Fruit yield (kg/tree) fresh weight

200

Fig. 3. Relationship between mean fruit mass (top) or biomass (bottom) and fruit yield per tree for ‘Empire’ apple trees receiving 0%, 3% or 12% applications of PKPF for a 6 year period (2005–2010).

PKPF was intermediate (21.06b, 21.49a and 21.27ab, respectively) These results, while not clearly defining the most appropriate methodology to measure WUE, do support the idea that fruit yield or biomass should be included in the WUE response to the environment when using either gas exchange data or isotopic carbon discrimination. As documented in Glenn (2016), 3% and 12% PKPF treatments had greater fruit mass than control (Fig. 3 top). However, there was no indication that PKPF treatments altered dry matter partitioning as suggested by Glenn and Puterka (2007) (Fig. 3 bottom). Radiation use efficiency was significantly greater for 3% and 12% PKPF (1.7 and 1.7 kg/GJ/m2 ) compared to control (1.5 kg/GJ/m2 ). These values are slightly greater than Monteith and Moss (1977) value of 1.4 kg/GJ/m2 . The increased RUE is due in part to the increased light reflection into the canopy (Glenn, 2016; Glenn and Puterka, 2007). The increased RUE likely drives increased E and A resulting in the reduced WUE measured with 13 C and the increased yield response (Figs. 2 and 3). 3.1. Lysimeter study 2015 The lysimeter study compared an untreated tree E to a PKPF treated tree E that was normalized relative to the untreated tree using pretreatment baseline level daily E amounts. After washing, the treated tree had E that was 71.9% of E in the control for DOY’s 229–235 indicating little or no change in the transpiration potential of the treated tree relative to the untreated control since the pretreatment difference was 70.12%. The relationship between E and the PKPF residue amount demonstrates that PKPF does increase E relative to an untreated control over a wide range of residue levels (Fig. 4). Residue levels in the 1–5 g/m2 range can be developed in commercial settings, although 1–3 g/m2 are probably more common. Within these ranges, E is consistently increased for a treated tree relative to its untreated control. E is not reduced until excessive residue amounts are applied (>20 g/m2 ) which likely physically block transpiration. This study did not measure A but Glenn and Yuri (2013) demonstrated that PKPF residues reduced PAR transmission

Leaf isotopic carbon discriminaon ( o/oo)

Biomass (kg/tree) dry mass

Control y = -0.1617x + 129.85 R² = 0.18

Normalized treatment (% of control)

D.M. Glenn / Scientia Horticulturae 205 (2016) 127–132

Mean fruit mass (g/fruit)

130

Control

3% PKPF

12% PKPF

22 21.5 21 y = -0.034x2 + 0.5573x + 19.662 R² = 0.45

20.5 20 19.5 0

2

4

6

8

10

Mean daily tranpiraon (mmol/m2/s) Fig. 5. Relationship between mean daily transpiration measured in whole canopy gas exchange chambers and the isotopic carbon discrimination values of leaves sampled from 2005 to 2010 for ‘Empire’ apple.

in a curvi-linear manner (ey = 0.0018 ×2 − 0.1192x + 4.5565; where y is PAR transmission (%) and x is the residue level (g/m2 )). Therefore, at 1, 3 and 5 g/m2 , 85%, 67% and 53%, respectively, of PAR is transmitted through the particle film. At full sun, the exposed exterior of the canopy is still light saturated at 5 g/m2 (700–800 ␮mol/m2 /s; Tartachnyk and Blanke, 2004) although Le Grange et al. (2002) documented reduced A in the interior of PKPF treated trees. PKPF studies document that the particle film reduced leaf and canopy temperature (Anandacoomaraswamy et al., 2000; Glenn and Puterka, 2007; Rosati et al., 2006, 2007; Wünsche et al., 2004; Boari et al., 2015; Glenn, 2010; Jifon and Syvertsen, 2003; Moftah and Al-Humaid, 2005; Steiman et al., 2011; Melgarejo et al., 2004). Furthermore, a reduction in leaf temperature generally increased stomatal conductance (Thorpe et al., 1980; Hetherington and Woodward, 2003) via the reduction in the leaf-to-air vapor pressure deficit and WUE generally declines with increased stomatal conductance (Jones, 1986). This general response was confirmed by comparing mean daily transpiration in the whole canopy chambers with the 13 C of the same trees over the 6 year period (Fig. 5). These results demonstrate that increased WUE, expressed as 13 C, is inversely related to the transpiration rate. These lysimeter results strongly suggest that PKPF is reducing leaf temperature resulting in increased stomatal conductance that increased E which will reduce WUE under these well-watered conditions. PKPF reduced canopy temperature distribution (Fig. 6) under clear (Fig. 6 top) and overcast (Fig. 6 bottom) conditions. Increasing VPD increased transpiration over the study period (Fig. 7 top) while

D.M. Glenn / Scientia Horticulturae 205 (2016) 127–132

60

3.95 g/m2 PKPF

32-32.5

control

clear sky

31.5-32 31-31.5 30.5-31 30-30.5 29.5-30 0

5

10

control

15 20 25 Frequency (% of total)

30

Control y = 1.0964x + 19.121 R² = 0.46

PKPF

35

40

Daily transpiraon (kg/tree)

Canopy temperature (C )

32.5-33

131

pre-treatment control

50

pre-treatment PKPF

40 30 20

PKPF y = 0.7876x + 17.621 R² = 0.27

10 3.95 g/m2 PKPF

32-32.5

control

0

overcast sky

0

31.5-32

5

10

15

20

25

Mean daily vapor pressure deficit (kPa)

31-31.5 30.5-31 30-30.5 29.5-30 0

20

40 60 Frequency (% of total)

80

100

Fig. 6. Canopy temperature distribution of PKPF treated and control apple trees on a clear (top) and overcast (bottom) day (August 4 and 5, 2015, respectively).

decreasing the magnitude of PKPF treatment difference (Fig. 7 bottom). As stated earlier, residues >20 g/m2 likely blocked stomata. In this study, there were no differences in WUEchamber due to PKPF treatments or irrigation, despite yield effects (Glenn 2016; Fig. 3 top). The lysimeter study indicated that there was a chronic stress that was not mitigated by irrigation in which E was likely limited by hydraulic conductivity from soil to leaf since a reduction in leaf temperature increased E following PKPF treatment in these well watered trees. If leaf temperature is decreased, the leaf-air vapor pressure deficit is also reduced which will reduce the transpiration potential and the subsequent E as Anandacoomaraswamy et al. (2000) and Jifon and Syvertsen, (2003) demonstrated in tea and citrus, respectively. However this was not the response in the lysimeter study to PKPF treatment. E increased suggesting that while the reduction in the leaf-air vapor pressure deficit from PKPF treatment did reduce the transpiration potential, the subsequent reduction in leaf temperature increased stomatal conductance resulting in canopy E approaching or achieving the potential transpiration demand similar to Srinivasa Rao (1985) in tomato. The reduction in WUE by PKPF treatment is balanced by an increase in overall gas exchange and increased yield and quality (Fig. 3 top). 4. Conclusions Whether WUE is measured directly in whole plant chambers, estimated by biomass/unit evapotranspiration, or 13 C, fruit yield and total biomass influence WUE. The effect of yield on WUE may partly explain the variable WUE results found in the literature. 13 C analysis of WUE generally found that the untreated control had lower values and therefore higher WUE than PKPF treatments. Whole plant gas exchange analysis of WUE generally lacked the sensitivity to identify the treatment differences observed using 13 C analysis and those treatment differences identified were contrary to 13 C analysis. The lysimeter study supported the reduced WUE of PKPF treated plants by demonstrating increased E with a range of PKPF residue amounts. The lysimeter results suggest

Normalized transpiraon rao

Canopy temperature (C )

32.5-33

1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0

Normalized rao without pre-treatment data y = -0.0252x + 1.6186 R² = 0.33

Residue < 5 g/m2 20 > residue > 5 g/m2 Residue > 20 g/m2 pre-treatment

0

5 10 15 20 Daily mean vapor pressure deficit (mbar)

25

Fig. 7. Relationship between transpiration (top) or normalized transpiration ([PKPF/0.701]/control) (bottom) and vapor pressure deficit for PKPF treated and untreated apple trees.

that for well-watered and presumably non-stressed conditions, gas exchange is limited by hydraulic resistances including stomatal conductance, leaf temperature and the concomitant leaf-air vapor pressure deficit that influence stomatal conductance. When leaf temperature was reduced by PKPF, the response resulted in increased stomatal conductance and gas exchange, as measured by increased E. The assertion of increased gas exchange is supported by the significantly greater fruit mass of 3% and 12% PKPF treatments relative to fruit number (Fig. 3 top) (Glenn 2016). Acknowledgement The authors wish to thank Tessenderlo Kerley, Inc. for partial financial support of this research. References Aly, M., El-Megeed, N.A., Awad, R.M., 2010. Reflective particle films affect on sunburn, yield, mineral composition and fruit maturity of ‘Anna’ apple (Malus domestica) trees. Res. J. Agric. Biol. Sci. 6, 84–92. Anandacoomaraswamy, A., De Costa, W., Shyamalie, H.W., Campbell, G.S., 2000. Factors controlling transpiration of mature field-grown tea and its relationship with yield. Agric. Forest Meteorol. 103, 375–386. Boari, F., Cucci, G., Donadio, A., Schiattone, M.I., Cantore, V., 2014. Kaolin influences tomato response to salinity: physiological aspects. Acta Agric. Scand. Sec. B-Soil Plant Sci. 64, 559–571. Boari, F., Donadio, A., Schiattone, M.I., Cantore, V., 2015. Particle film technology: a supplemental tool to save water. Agric. Water Manage. 147, 154–162. Cantore, V., Pace, B., Albrizio, R., 2009. Kaolin-based particle film technology affects tomato physiology, yield and quality. Environ. Exp. Bot. 66, 279–288.

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