Leaf Wettability Research Articles

Modifications of the leaf surface structures of Quercus ilex L. in open, naturally CO2‐enriched environments

Two Italian CO2 springs allowed us to study the long‐term effect of a 350–2600 μmol mol–1 increase in CO2 concentrations on the surface structures of leaves of Quercus ilex L. Carbon dioxide increased the quantity of cuticular waxes, above an apparent threshold of 750 μmol mol–1 CO2. Leaf wettability was not modified by CO2 concentrations. Reduction in stomatal frequency was observable up to 750 μmol mol–1 CO2, the slope being almost the same as that estimated for the increase in CO2 concentration from pre‐industrial times to the present. At higher concentrations, CO2 seemed to exert no more impact on stomatal frequency.

Influence of epiphytic micro-organisms on leaf wettability: wetting of the upper leaf surface of Juglans regia and of model surfaces in relation to colonization by micro-organisms.

Wetting of the upper leaf surface of Juglans regia L. and of model surfaces colonized by epiphytic micro-organisms was investigated by measuring contact angles of aqueous solutions buffered at different pH values. During June to October 1995, contact angles of aqueous solutions on the leaf surface of J. regia decreased by angles ranging from 12° (low pH values) to 25° at high pH values. At the end of this vegetation period, wetting was strongly dependent on pH showing significantly lower contact angles with alkaline solutions (pH 9·0) than with acidic solutions (pH 3·0). Contact angle titration measured angles on the leaf surface as a function of the pH of buffered aqueous solutions, covering a pH range from 3·0 to 11·0. Titration curves revealed inflection points around 7·5, indicating the existence of ionizable carboxylic groups at the interface of the phylloplane. Altered leaf-surface wetting properties observed on the intact leaf surface could be simulated in model experiments by measuring contact angles on artificial surfaces colonized by Pseudomonas fluorescens and by epiphytic micro-organisms isolated from the phylloplane of J. regia. Strong evidence is provided that interfacial carboxylic groups derive from epiphytic micro-organisms present on the phylloplane. Results suggest that the age-dependent increase in, and pH dependence of, wetting as leaves mature are related to the presence of epiphytic micro-organisms on the phylloplane. Ecological consequences of increased leaf-surface wetting, concerning the structure of the leaf surface as a microhabitat for epiphytic micro-organisms, are discussed.

Relationships between transpiration, stomatla damage and leaf wettability in declining beech trees

In order to determine the relationship between transpiration, stomatal damage and leaf wettability in adult beech trees ( Fagus sylvatica L.) in situ, sample leaves were gathered from healthy trees and from declining trees, both at the beginning and at the end of the growing season. Four parameters were assessed in each leaf: transpiration in the field, transpiration in the laboratory after rehydration, stomatal damage index, and leaf-water drop contact angle. The results showed that the transpiration was linked to the health status of the tree only when the external conditions were least favourable, i.e. in the month of June in the field. During the season the index of stomatal damage increased considerably in declining trees, while the drop contact angle decreased. Linear regression between the transpiration and the stomatal damage indix did not show any significant correlation, thus suggesting - at least in the environmental conditions prevailing in thi experiment - structural alterations in the stomata were not capable of modifying the transpiration capacity. Lastly, contact angle data did not correlate significantly with either the transpiration or the stomatal damage index.

Effect of Rainfall Exposure on Leaf Wettability in Near-Isogenic Barley Lines with Different Leaf Wax Content.

Water retention, contact angle of water droplets, and amount of epicuticular wax on leaf surfaces were examined in two lines of near-isogenic barley with normal and glossy leaves. In addition, the effect of rainfall on the wettability of leaf surfaces was examined. Mean water retention of leaves from the 1st to 5th node was 5.6mg/cm2 in normal leaf lines and 12.8mg/cm2 in glossy leaf lines. The mean contact angle of water drops was 125° in normal leaf and 93° in glossy leaf. The mean epicuticular wax content was 17.3μg/cm2 in normal leaf and 9.3μg/cm2 in glossy leaf. In glossy leaves, contact angles decreased with increasing duration of rainfall treatment. After treatment for 5 days, the angle was about 70% of that without rainfall treatment. Reduction of epicuticular wax amount by rainfall exposure occurred in all leaf positions of both barley lines. The reduction rates in the normal leaf line were 10-20%. In the glossy leaf line, the reduction rates were 15% in the 1st leaves and about 50% in the 2nd-3rd leaves.

Patterns of leaf surface wetness for montane and subalpine plants

ABSTRACTThe frequency and duration of water on leaf surfaces have important consequences for plant growth and photosynthetic gas exchange. The objective of the present study was to compare the frequency and duration of leaf wetness under natural field conditions among species and to identify variation in structural features of leaves that may reduce surface wetness. During June–September 1992 in the central Rocky Mountains (USA), natural leaf wetting due to rain and dewfall was observed on 79 of 89 nights in open meadow habitats compared to only 29 of 89 nights in the understorey. Dew formation occurred at relative humidities that were often well below 100% because of radiational heat exchange with cold night skies and low wind speeds (< 0.5 m s−1). A survey of 50 subalpine/montane species showed that structural characteristics associated with the occurrence and duration of leaf surface wetness differed among species and habitats. Both adaxial and abaxial surfaces accumulated moisture during rain and dewfall events. Leaf surfaces of open‐meadow species were less wettable (P= 0.008), and had lower droplet retention (P= 0.015) and more stomata P= 0.017) than adjacent understorey species. Also, leaf trichomes reduced the area of leaf surface covered by moisture. Ecophysiological importance is suggested by the high frequency of leaf wetting events in open microsites, influences on growth and gas exchange, and correspondence between leaf surface wettability and habitat.

Effects of Ultraviolet-B Radiation and Acid Mist on Growth and Leaf Wettability o Radish Plants

Radish plants were grown in chambers (PPFD 300μmol m-2 s-1, day length 14h, 21°C, 70%RH) for 10 days, under UV-B irradiation (UV-BBE; 0, 6.5 (low) and 8.6 (high) kJ m-2 d-1) for 12h a day; the plants were exposed to acid mist (pH 3.0 and 5.6) every 2 days. At the end of the treatments, leaf area, dry weights of shoot and hypocotyl, total chlorophyll content, water loss rate and water droplet contact angle (DCA), which is a measure of wettability, on adaxial and abaxial leaf surfaces were determined in each of 9 combinations of treatments, 3 (UV-B)×3 (mist, including no mist). UV-B radiation significantly decreased leaf area and dry weights of shoot and hypocotyl, and increased total chlorophyll content per unit leaf area. Similarly, acid mist of pH 3.0 significantly decreased leaf area and hypocotyl dry weight. However, no combined effect of UV-B and mist on these growth parameters and chlorophyll content was found. On the other hand, there were significant combined effects on DCA on both adaxial and abaxial surfaces; at the high UV-B level, DCA on adaxial surfaces of treated leaves with mist decreased, although that of untreated leaves increased.

The influence of UV-B radiation on the physicochemical nature of tobacco (Nicotiana tabacumL.) leaf surfaces

Relationships between leaf wettability and surface physicochemical characteristics were examined in two genotypes of tobacco (Nicotiana tabacum L. cv. Samsun) grown under controlled conditions at three different levels of biologically effective ultraviolet-B (UV-BBE; 280–320 nm) radiation; 0 (control), 4.54 and 5.66 kJ m–2d–1. Leaf wettability, assessed by measuring leaf-water droplet contact angles, was positively correlated with epicuticular wax chemical composition and trichome density, but not the amount of wax on the surface of leaves. Tobacco wax comprised a mixture of C19–C33 n-alkanes (59%) with homologues containing an odd number of carbon atoms predominating, C28–C32 br-alkanes (38%), and a small quantity (3%) of free Cl6–C18 fatty acids. Significant effects of UV-B radiation upon wax production and chemical composition were restricted to the adaxial surface of leaves. Enhanced UV-B radiation reduced the quantity of epicuticular wax in the more sensitive genotype [GR32-3], assessed from effects on dry matter accumulation, partitioning and changes in leaf morphology, and resulted in marked changes in wax composition and homologue distributions in both genotypes. UV-B-induced increases in branching, and shifts toward the synthesis of shorter-chain homologues provided evidence for a fundamental effect of UV-B radiation on wax biosynthesis, with the observed effects consistent with a highly specific and direct effect of UV-B radiation on microsomal-based elongases in the epidermis. UV-B radiation also reduced the density of trichomes on the adaxial leaf surface, whilst increasing the number of trichomes on the abaxial leaf surface. Changes in wax composition and trichome density induced by UV-B radiation were associated with increases in leaf surface wettability which were particularly pronounced on the adaxial surface. The subtle, though possibly far-reaching, physiological consequences of such UV-B-induced changes in surface wettability are discussed in the light of other recent findings.

LEAF SURFACE WETNESS AND GAS EXCHANGE IN THE POND LILY NUPHAR POLYSEPALUM (NYMPHAEACEAE)

As part of a continuing study of the effects of leaf surface wetness on gas exchange, the occurrence of leaf surface wetting by dewfall and associated effects on photosynthesis were evaluated for floating and aerial leaves of the pond lily Nuphar polysepalum Engelm. Because of nighttime radiation exchange with a cold sky, high humidity, and the presence of adaxial stomata, we predicted that pond lily leaves would be particularly susceptible to wetting events such as dewfall. A substantial reduction in net photosynthesis (up to 20%) occurred for leaves that were experimentally misted to simulate leaf wetting by dewfall. Aerial leaves remained below dewpoint temperatures for long periods on clear nights. However, floating leaves rarely approached dewpoint temperatures at night because minimum nighttime temperatures of leaves were up to 10 C warmer than air temperature. Thus, floating leaves of N. polysepalum did not experience dew formation primarily because of strong thermal coupling to a substrate (water) that was much warmer than air temperature at night. This coupling to a warmer substrate prevented a potentially strong inhibition of photosynthetic CO2 exchange the following morning.

Leaf Surface Wetness and Gas Exchange in the Pond Lily Nuphar polysepalum (Nymphaeaceae)

As part of a continuing study of the effects of leaf surface wetness on gas exchange, the occurrence of leaf surface wetting by dewfall and associated effects on photosynthesis were evaluated for floating and aerial leaves of the pond lily Nuphar polysepalum Engelm. Because of nighttime radiation exchange with a cold sky, high humidity, and the presence of adaxial stomata, we predicted that pond lily leaves would be particularly susceptible to wetting events such as dewfall. A substantial reduction in net photosynthesis (up to 20%) occurred for leaves that were experimentally misted to simulate leaf wetting by dewfall. Aerial leaves remained below dewpoint temperatures for long periods on clear nights. However, floating leaves rarely approached dewpoint temperatures at night because minimum nighttime temperatures of leaves were up to 10 C warmer than air temperature. Thus, floating leaves of N. polysepalum did not experience dew formation primarily because of strong thermal coupling to a substrate (water) that was much warmer than air temperature at night. This coupling to a warmer substrate prevented a potentially strong inhibition of photosynthetic CO2 exchange the following morning.

Foliar Nitrogen Fertilization of Citrus in Florida

Foliar applications of urea nitrogen (N) is a relatively new practice in Florida citrus production resulting from applied research and changes in citrus fertilizer management philosophy. The present study investigated the effect of leaf age and surface morphology on leaf wettability as measured by contact angles, and absorption efficiency of foliar-applied N. Young leaves (0.25 and 1 month) were more efficient than old leaves in the absorption of foliar-applied N. Contact angles of water, urea-, and triazone-N solutions were low in the young leaves. The adaxial surfaces had lower contact angles than abaxial surfaces in each leaf age group. Inefficient N absorption and large contact angles in old leaves (3 and 6 months) were related to surface wax deposition and cuticle thickness, which increased with leaf age. 15N- and 14C-labeled urea are being used to determine precisely how the cuticle and wax affect foliar N absorption in citrus leaves.

Leaf surface properties of Norway spruce needles exposed to sulphur dioxide and ozone in an open‐air fumigation system at Liphook

ABSTRACTSamples of current‐year and 1‐year‐old foliage were taken from Norway spruce (Picea abies (L.) Karst.) trees in April 1991, 4 months after a 3–4 year controlled fumigation with O3 and SO2 in the open at Liphook, south‐east England. Trees were grown in seven plots, and treated in a factorial design with three levels of SO2 and two levels of O3 (ambient and c. 1.3 × ambient), with an extra ambient air plot. All statistical analyses were made on plot means.Leaf wettability, as measured by the contact angle of water droplets, was significantly affected by needle age and by SO2 treatment (P≤0–05. in older needles, decreasing with increasing SO2 concentration. There was no effect of O3 on wettability, and no effect of any treatment on amounts of surface wax extracted by immersion of needles in chloroform. Electrolyte leakage rates from detached current‐year needles were not affected by prior exposure to O3, but decreased significantly (P= 0.034) with increasing exposure to SO2. There was no detectable effect of fumigation on the rate of water loss from detached needles. Similarly, there was no effect of fumigation on the dry weight/fresh weight ratio of needles. The total sulphur content of needles increased significantly (P≤0.0001) with exposure to SO2 and with needle age. Amounts of water‐extractable sulphate, however, varied greatly among plots, but with no pattern with respect to fumigation treatment.It is concluded that leaf wettability and electrolyte leakage rates may be good indicators of the persistent effects of SO2 on Norway spruce growing in the open air, and that the observed changes in leaf surface properties in response to SO2 fumigation have implications for the processes, both biotic and abiotic, that occur on leaf surfaces.

An Empirical Model for Predicting the First Symptoms of Sooty Blotch and Flyspeck of Apples

Measures of leaf wetness duration were related to the appearance of symptoms of sooty blotch (caused by Peltaster fructicola, Leptodontium elatius, and other fungi) and flyspeck (caused by Zygophiala jamaicensis) on apple (Malus x domestica) during the 1987 through 1994 growing seasons. Hours of leaf wetness of 4 h duration or greater accumulated from the first rain that occurred 10 days after petal fall provided the best measure of the time of symptom appearance. Over the 8 years of the study, symptoms appeared after an average of 273 h of leaf wetting (range 209 to 310 h). No consistent temperature effects on the time of first symptom appearance were found. A threshold value of 200 to 250 h of leaf wetting is suggested to initiate fungicide applications for the control of sooty blotch and flyspeck.

Rate Response of Bacillus Thumngiensis Against Leafrollers, 1992

Abstract Bt products were evaluated for their effect on PLR larvae using a leaf-disk bioassay. A series of Bt concentrations ranging from 0.5 to 5 times the recommended field rates were tested. Untreated apple leaves were collected from Red Delicious trees at the WSU Tree Fruit Research and Extension Center, Wenatchee. Bt products were diluted in 500 ml of water plus 2 u,l of X-77, a wetting agent added to aid leaf wetting. An untreated control was prepared using water plus the wetting agent only. Leaves were dipped and allowed to dry. Two disks (2.3 cm diameter) were taken from each leaf. Four leaf disks were placed in a petri dish (Falcon 1006, 50x9 mm). Five one- to two-d-old leafroller larvae were placed on the leaf-disks and the petri dish lid was put in place. Ten dishes were used for each Bt product and rate (50 larvae per treatment). Dishes were placed inside a food storage container with a wet paper towel to maintain a high humidity and kept at 75°F (±2°F) constant temperature and 16:8 photoperiod. Dishes were examined after 48 and 96 h to determine larval survival. Data were corrected for untreated mortality using Abbott’s formula.

Functional interaction between leaf trichomes, leaf wettability and the optical properties of water droplets

Abstract. Because CO2 diffuses 10000 times more slowly through water than air, there may be strong selective pressure for increased water repellency in terrestrial plant leaves. In the present study, leaf trichomes appeared to have a strong influence on leaf water repellency (i.e. degree of water droplet formation on the leaf surface) as well as the retention of droplets on the leaf. Based upon evaluation of 38 plant species from 21 families, we found that leaves with trichomes were more water repellent, especially where trichome density was greater than 25mm2. However, droplet repellency and retention were both high in some species where trichomes entrapped droplets. Finally, the lensing effects of water droplets on leaf surfaces increased incident sunlight by over 20‐fold directly beneath individual droplets. These results may have important implications for such processes as stomatal function, whole leaf photosynthesis, and transpiration for a large variety of plant species.

Effects of simulated acidic rain on upper leaf surface of Zea mays foliage

Experiments were conducted to determine the histological effects of simulated acidic rain on the cuticle of Zea mays L. cv. B73 × Mo 17 and to ascertain whether subsequent drought stress might elicit interacting effects. Greenhouse-grown plants were treated twice weekly with simulated acidic rain of pH 5.0 or 3.0 for 3–4 weeks. Half of the plants in each pH treatment were then subjected to a 10-day drought stress by withholding water, while the remaining plants continued to receive rain treatments. At the end of the treatment period, leaf tissue was sampled and fixed for light or scanning electron microscopy. Small elongated white lesions approximately 1 mm in diameter appeared in a random pattern on leaves 5–7 that were treated with rain of pH 3.0 for 3 weeks. Plants treated with rain of pH 5.0 did not exhibit these lesions. Lesions were clearly defined areas of collapsed necrotic tissue extending through the leaf. Within lesions, the basal region of 50% of the trichomes had collapsed bases in confluence with adjacent cells. Epicuticular morphology was unaffected by simulated acidic rain or drought stress and appeared as a crystalline platelet-like formation. From our observations, it appeared that factors that maximized droplet retention or droplet deposition, e.g., leaf wettability and leaf orientation, maximized lesion formation. Drought stress had no observable influence on the cuticle of plants treated with either simulated acidic rain treatment. Key words: corn, acid rain, drought stress, histology, cuticle, transpiration.

Relationship between Leaf Wetness Period, Temperature and Infection of Venturia nashicola to Japanese Pear Leaves.

The relationship between leaf wetness period, temperature and infection to Japanese pear leaves by artificial inoculation with conidia of Japanese pear scab fungus, Venturia nashicola, was investigated. The inoculated leaves developed symptoms slightly with 9-hr leaf wetting at 15°C, moderately with 12-hr leaf wetting at 5 and 25°C, and more heavily at 15 to 20°C. Leaves did not show, however, any symptoms at 30°C even with 36-hr leaf wetting, or less than 6-hr leaf wetting even at 5 to 25°C. These results are strikingly similar to those reported for apple scab by Mills. And these results coincide with the conidial and ascosporous germination status on water agar medium kept at 5 to 30°C, and behavior of conidial germination and penetration into leaf tissue with different wetting period kept at about 20°C. Based on the result that pathogenicity of ascospore is almost the same as conidial one, these results seem to be applied to the infection by ascospores.

Effect of Surface-Active Pseudomonas spp. on Leaf Wettability

Different strains of Pseudomonas putida and P. fluorescens isolated from the rhizosphere and phyllosphere were tested for surface activity in droplet cultures on polystyrene. Droplets of 6 of the 12 wild types tested spread over the surface during incubation, and these strains were considered surface active; strains not showing this reaction were considered non-surface active. Similar reactions were observed on pieces of wheat leaves. Supernatants from centrifuged broth cultures behaved like droplets of suspensions in broth; exposure to 100 degrees C destroyed the activity. Average contact angles of the supernatants of surface-active and non-surface-active strains on polystyrene were 24 degrees and 72 degrees , respectively. The minimal surface tension of supernatants of the surface-active strains was about 46 mN/m, whereas that of the non-surface-active strains was 64 mN/m (estimations from Zisman plots). After 6 days of incubation, wheat flag leaves sprayed with a dilute suspension of a surface-active strain of P. putida (WCS 358RR) showed a significant increase in leaf wettability, which was determined by contact angle measurements. Increasing the initial concentration of bacteria and the amount of nutrients in the inoculum sprayed on leaves reduced the contact angles from 138 degrees on leaves treated with antibiotics (control) to 43 degrees on leaves treated with surface-active bacteria. A closely related strain with no surface activity on polystyrene did not affect leaf wettability, although it was present in densities similar to those of the surface-active strain. Nutrients alone could occasionally also increase leaf wettability, apparently by stimulating naturally occurring surface-active bacteria. When estimating densities of Pseudomonas spp. underneath droplets with low contact angles, it appeared that populations on leaves treated with a surface-active strain could vary from about 10 to 10 CFU cm, suggesting that the surface effect may be prolonged after a decline of the population. The possible ecological implications are discussed.

Regional variation in surface properties of Norway spruce and scots pine needles in relation to forest decline

Measurements of leaf wettability (contact angle), amounts of epicuticular wax and of surface dust are reported for Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies (L) Karst) trees growing at 12 sites in Europe from SW Germany to NE Scotland. At each site, three year classes (current year, 1 and 2-year-old) of needles were sampled from the mid-crown of up to 12 trees. Trees were selected at random from two strata, those showing visible decline symptoms (i.e. loss of needles or discoloration) and those apparently healthy. Needles for analysis were taken from apparently healthy (green) shoots in both cases. There were no significant differences between ‘declining’ and ‘healthy’ trees within sites, suggesting that leaf surface properties reflect environmental exposure rather than plant response. There were signiicant differences between sites, particularly for Norway spruce, which may be related to environmental factors including air pollution. Contact angles were consistently smaller at low-altitude sites in Britain and The Netherlands than at high-altitude sites in Germany where forests show decline symptoms. Leaf wettability decreased (contact angles increased) with wax amount and increased with dust amount. Leaf surface properties integrate environmental influences over long periods, and may be useful in identifying sites ‘at risk’ of developing decline symptoms, but causal relationships cannot be deduced without further direct experimentation.

Effects of simulated acid rain on leaf wettability, rain retention and uptake of some inorganic ions.

Leaves of Phaseolus vulgaris L., Vicia faba L., Pisum sativum L. and Brassica napus L. were exposed from emergence to full expansion to seven treatments of simulated acid rain at pH values between 5.6 and 2.6. Droplet leaf contact angles in all species decreased on leaves exposed to simulated acid rain at pH <4.6 relative to those exposed at pH 5.6. Retention of rain containing fluorescein increased on P. vulgaris leaves exposed to simulated acid rain at pH 4.6 and at pH < 3.8. Retention by B. napus leaves was increased at pH < 4.6. Uptake of the three ions studied was in the order 86 Rb+ ≤35 SO4 2- ≤63 Ni2+ . Uptake of 86 Rb+ increased into B. napus leaves and decreased into P. vulgaris leaves exposed at pH ≤ 3.4. Uptake of 35 SO4 2- and 63 Ni2+ by B. napus leaves increased after exposure to simulated acid ruin at pH 2.6 but it was unaffected in P. vulgaris. Up to 7%, of applied 35 SO4 2- , was found in the epicuticular wax layer on B. napus leaves 48 h after application, most being found after exposure at pH 2.6. The order of lateral movement of ions within leaves paralleled the order of uptake. Movement of all three ions was increased in B. napus leaves exposed previously to simulated acid rain at pH 2.6. The increased retention of fluorescein on leaves exposed to simulated acid rain and the reduced contact angles for water are attributed to decreases in surface roughness. The altered ion uptake pattern could also be related to changes in surface wax structure or could be associated with observed changes in properties of cuticular membranes. These results demonstrate that the interaction of plants with their atmospheric environment could possibly be affected by pre-exposure to acid rain in amounts and at pH values that occur in ambient rainfall.

EFFECTS OF SIMULATED ACID RAIN ON PRODUCTION, MORPHOLOGY AND COMPOSITION OF EPICUTICULAR WAX AND ON CUTICULAR MEMBRANE DEVELOPMENT

SummaryLeaves of Phaseolus vulgaris L., Vicia faba L., Pisum sativum L. and Brassica napus L. were exposed to simulated rain from emergence to full expansion at seven pHs between 5.6 and 2.6, applied at 2 mm h−1 in amounts and at intervals representative of ambient rain in southwestern England. Leaf expansion was unaffected by rain pH greater than 30 in V. faba, and pH 2–6 in the other species. Macroscopic foliar injury was induced at pH 3.4 in non‐wettable leaves of P. sativum and B. napus which had relatively large deposits of crystalline epicuticular wax, and at pH 3.0 in wettable leaves of P. vulgaris and V. faba which had small deposits of amorphous wax. Foliar injury was greatest in species with crystalline wax. Wax production was affected by simulated acid rain in all species and was often accompanied by changes in wax composition. Wax quantity was reduced on leaves of P. vulgaris exposed to rain at pH 4.6, while wax on leaves of P. sativum and B. napus had increased numbers of smaller plates and tubes, respectively, per unit area at pH 4.6. Leaves of B. napus, stripped of crystalline epicuticular wax at about 20% full expansion, regenerated less wax at pH 3.4 than at pH 5.6. The thickness of the cuticular membranes in leaves of P. vulgaris, V faba and P. sativum exposed to simulated acid rain at pH 4.2 decreased by 28 to 35 % compared with those exposed to pH 5.6 rain. Membrane ultrastructure was also altered in leaves of P. vulgaris. Taken together, these changes could have important consequences for leaf wettability, rainfall retention, foliar uptake of chemicals and host‐parasite interactions.