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Ann Bot. 2016 May; 117(6): 1045–1052.
Published online 2016 March 26. doi:  10.1093/aob/mcw025
PMCID: PMC4866312

Retain or repel? Droplet volume does matter when measuring leaf wetness traits

Abstract

Background and Aims Leaf wetness is an important characteristic linked to a plant’s strategies for water acquisition, use and redistribution. A trade-off between leaf water retention (LWR) and hydrophobicity (LWH) may be expected, since a higher LWH/lower LWR may enhance photosynthesis, while the opposite combination may increase the leaf water uptake (LWU). However, the validation of the ecological meaning of both traits and the influence of droplet volume when measuring them have been largely neglected.

Methods To address these questions, LWR and LWH of 14 species were measured using droplets of between 5 and 50 μL. Furthermore, the ability of those species to perform LWU was evaluated through leaf submergence in water. The droplet-volume effect on absolute values and on species ranking for LWR and LWH was tested, as well as the influence of water droplet volume on the relationship between leaf wetness traits and LWU.

Key Results Variations in droplet volume significantly affected the absolute values and the species ranking for both LWR and LWH. The expected negative correlation between leaf wetness traits was not observed, and they were not validated as a proxy for LWU.

Conclusions The water droplet volume does matter when measuring leaf wetness traits. Therefore, it is necessary to standardize the methodological approach used to measure them. The use of a standard 5 μL droplet for LWH and a 50 μL droplet for LWR is proposed. It is cautioned that the validation of both traits is also needed before using them as proxies to describe responses and effects in functional approaches.

Keywords: Contact angle hysteresis, foliar water uptake, leaf hydrophobicity, leaf water repellency, leaf water retention, throughfall

INTRODUCTION

Plant species differ greatly in their ability to retain or repel water droplets on leaf surfaces (Neinhuis and Barthlott, 1997; Aryal and Neuner, 2010). After leaf wetness events caused by rain, fog, dew or mist, super-hydrophilic leaves may become covered by a water film or by many flattened droplets, while highly non-wettable surfaces may repel water by forming almost spherical-shaped droplets. In some species, the water droplets easily drain off of the leaves, but in others they remain strongly adhered to foliar surfaces even at steeper leaf inclination angles (Brewer et al., 1991; Aryal and Neuner, 2010). These differences in leaf water hydrophobicity (LWH) and leaf water retention (LWR) may reflect distinct strategies related to plant water acquisition, use and redistribution (e.g. Holder, 2007; Aryal and Neuner, 2010).

As the presence of a water film on the leaf surface can significantly reduce the gas exchange by reducing CO2 diffusion and occluding stomatal apertures, there should be a strong selective pressure to repel water droplets from the leaf surface, especially for plants inhabiting very wet areas (Smith and McClean, 1989; Brewer et al., 1991; Holder, 2012). In fact, this hypothesis has been corroborated by studies that found higher LWH and lower LWR values in species from open areas – where leaf wetness events are generally more frequent (Jordan and Smith, 1994) – than in understorey species (e.g. Brewer and Smith, 1997; Pandey and Nagar, 2003).

In arid and semi-arid environments, plants may exhibit highly repellent leaf surfaces due to the presence of high-density trichomes and hydrophobic epicuticular waxes (Holder, 2012). Usually seen as a specialization to minimize water loss and overheating (Schreuder et al., 2001), these features can also promote low leaf wettability and then contribute to higher throughfall rates during the rare periods of precipitation (Holder, 2012). Hence, in such habitats, highly repellent leaves might not only enhance gas exchange and photosynthetic efficiency, but also increase water availability to root systems (Holder, 2012). Additionally, by avoiding the persistence of water films on leaves, plants can also reduce the incidence of pathogens (Reynolds et al., 1989), the colonization of epiphylls (Holder, 2007), pollutant deposition (Neinhuis and Barthlott, 1998; Klemm et al., 2002), ice formation (Aryal and Neuner, 2010), and tissue damage caused by focusing sunlight (Brewer et al., 1991). Therefore, repelling water droplets from leaves seems to be an advantage in either wet or dry environments since it may be related to distinct ecological processes (Smith and McClean, 1989; Brewer et al., 1991; Holder, 2007; Rosado et al., 2010). However, staying wet all over is not always detrimental. Under some circumstances, an ability to retain water droplets on leaves, instead of repelling them, can be beneficial to plants. The evaporation of water films reduces leaf temperature, eases heat stress and decreases transpiration rates (Katata et al., 2010). As a result, plants can absorb CO2 at a low water cost and keep a positive carbon balance, even under soil water deficits (Simonin et al., 2009; Ben-Asher et al., 2010). Some plants are also able to absorb water directly through their leaves (Goldsmith et al., 2013). It has been shown that leaf water uptake (LWU) can contribute up to 42 % of the total leaf water content (Eller et al., 2013) and can significantly improve plant water status, by decreasing stomatal conductance, recovering xylem cavitation, increasing shoot water potential and positively affecting plant survivorship and growth (Limm et al., 2009; Simonin et al., 2009; Eller et al., 2013). In areas where dew and fog events co-occur with dry-soil conditions, LWU may be an important mechanism for plant hydration (e.g. Limm et al., 2009; Goldsmith et al., 2013), and then a selective pressure for reducing LWH and increasing LWR should be expected (Simonin et al., 2009; Rosado and Holder, 2013). Alternatively, lower LWH observed in plants exposed to artificial fog (Eller et al., 2013) or inhabiting moist forests (Neinhuis and Barthlott, 1997) and fog-affected environments (Holder, 2007) may be simply caused by the erosive effect of the water on leaf epicuticular waxes, and does not necessarily reflect an adaptive plant response.

Since leaf wetness events may have both negative and positive effects, a continuum is expected between the two opposite plant strategies, from the species able to perform LWU (lower LWH and higher LWR) to the species that avoid water films on the leaf surfaces by throughfall (higher LWH and lower LWR) (Konrad et al., 2012; Fernández et al., 2014). Although quite plausible, the relationships among leaf wetness traits and these ecophysiological processes have not yet been validated at the species or community levels. As proposed by Rosado et al. (2013), the validation of traits is needed to test whether they can truly be used as proxies to predict plant responses. Furthermore, the relationship between LWH and LWR is uncertain, since the expected negative correlation has been found in some studies (Brewer and Smith, 1997; Brewer and Nuñez, 2007), but not in others (Pandey and Nagar, 2003; Holder, 2012).

The discrepancy among studies may be related to methodological artefacts in the functional trait-based approach used to evaluate LWH and LWR. Usually, LWH has been assessed by calculating the contact angle between the leaf surface and the line tangent to a sessile water droplet through the point of contact (Aryal and Neuner, 2010; Rosado and Holder, 2013). As the contact angle increases, the amount of leaf area covered by the water droplet decreases. Thus, greater contact angles indicate a more spherical water droplet and a more water-repellant surface (Rosado and Holder, 2013). In turn, LWR has been defined as the angle of tilt in which a water droplet begins to move or downslide as a leaf is incrementally tilted from 0 to 90°. High angular values indicate a greater tendency to retain droplets, while low values indicate leaf surfaces that readily shed droplets (Brewer, 1996).

According to Brewer (1996), these measurements could be made using droplets of different sizes to simulate different leaf wetness sources, such as rain, fog, dew or garden sprinklers. Reviewing several papers that measured leaf wetness traits, Rosado and Holder (2013) found that water droplets from 1 to 10 μL (5 μL is the most often used) have been used to determine LWH, while for LWR the range is from 10 to 50 μL (50 μL is the most often used). In the handbook for the measurement of plant traits, Pérez-Harguindeguy et al. (2013) suggested droplets from 2 to 5 μL to measure LWH, but no standard value was proposed for LWR. Although Schreiber (1996) found that there were no significant differences for LWH among droplets from 1 to 10 μL, this study was performed on only one species, which reduces the possibility of expanding this result to create a general rule. To the best of our knowledge, there have not yet been any studies investigating whether water droplet size influences LWR.

Taking into account the importance of leaf wetness for ecological processes in different hierarchical levels (e.g. from leaf to ecosystem), our aims were as follows: (a) to test if the changes in droplet water volume significantly affect the values of LWH and LWR, as well as the relationship between these two traits; (b) to evaluate the consistency of species ranking based on these traits when using different water droplet volumes; and (c) to validate whether these traits may be used as proxies to predict species’ ability to perform LWU

MATERIALS AND METHODS

Sites and species

We collected leaves of 14 species from two sites: Parque Nacional da Floresta da Tijuca and Parque Nacional de Itatiaia, both located in Rio de Janeiro state, Brazil (Table 1). Tijuca Forest (22°57'S, 43°18'W) is a remnant of the Atlantic rain forest located inside Rio de Janeiro city, and has a tropical wet climate (Aw, Köppen classification) with a mean annual temperature of 21 °C and a mean annual precipitation of 2500 mm (Brasília, 2008). The high-altitude plateau (with an average elevation of about 2400 m) of Itatiaia (22°21'S, 44°40'W) is covered by grassland vegetation and has a high land tropical climate (Cwb, Köppen classification) with a mean annual temperature of 18 °C and a mean annual precipitation of 2400 mm (Segadas-Vianna and Dau, 1965; Safford, 1999). The selected species are common in their sites, differ in the presence/absence of foliar trichomes and have leaves large enough to enable the allocation of droplets of different volumes.

Table 1
Mean ± s.d values for leaf water retention (LWR) (50 μL), leaf water hydrophobicity (LWH) (5 μL), leaf water uptake – percentage increase in leaf water content after leaf submergence in distilled water (LWU) ...

Measurement of leaf wetness traits

Ten branches of each species were collected (May and June 2015), transported to the laboratory and stored in the refrigerator until the measurements. For each branch, five mature healthy leaves were sampled, dried with a non-abrasive absorbent filter paper and pinned onto a styrofoam flat platform. A droplet of milli-Q water was placed onto the leaf surface using a micropipette (P100, Pipetman, Gilson SAS, Villiers-le-Bel, France). To measure LWH, a photograph of the water droplet resting on the horizontal leaf surface was taken with a digital camera (Exmor R CMOS, 1/2·3'', 20·4 Megapixel, Sony, Tokyo, Japan). From the digital image, the contact angle was determined using the free software ImageJ, version 1.48. To measure LWR, the platform was progressively tilted from 0 to 90°, and the angle of tilt in which the water droplet moved was determined using a protractor. A retention angle of 90° was assigned to the samples that, after the complete tilting of the platform, did not show droplet movement. To consider the range of droplet volumes observed in the literature (Rosado and Holder, 2013), LWR and LWH were measured using water droplets of five different volumes: 5, 10, 15, 25 and 50 μL. Measurements of both adaxial and abaxial leaf surfaces on 50 leaves per species, ten for each droplet volume, were conducted.

Measurement of leaf water uptake

The ability of a species to perform LWU was determined based on the protocol proposed by Limm et al. (2009). For each species, five branches were collected, placed between damp sheets of paper, sealed in zip-lock bags and maintained at 5 °C in the dark for 72 h to ensure a standard degree of turgor for all samples. After rehydration, one mature healthy leaf per branch was chosen and allowed to dry on the bench for 3 h in a 20 °C room. The initial mass (m1) was determined and then the petiole was sealed with vaseline to prevent evaporation. The whole leaf lamina was submerged in distilled water in darkness. The complete leaf submergence was used to standardize water availability across the morphologically diverse foliar types and represented the maximum quantity of water that a plant could absorb through the leaves. After 3 h, the leaf was removed from the water, dried with paper towels and the mass after this first submergence was recorded (m2). To account for any potential error associated with residual water on the leaf surface, the leaf was allowed to dry on the bench for 5 min and then the mass was recorded again (m3). The same leaf was re-submerged in water for 1 s, dried with paper towels and immediately re-weighed (m4). This brief re-wetting did not allow sufficient time for water absorption, so any increase in mass associated with this second submergence represented the residual water on the leaf surface. Finally, all leaves were dried at 50 °C for 96 h to determine the dry mass (mdry). The ability of a species to perform LWU was calculated as the increase in leaf water content after submergence, using: LWU (%) = {[m2 – (m4m3) – mdry]/(m1mdry) –1} × 100. For one species, it was not possible to perform the LWU experiment, due to a lack of sufficient samples.

Statistical analysis

Nested analysis of variance (ANOVA) followed by pairwise t-tests were used to assess whether there were significant differences in LWR and LWH values among sites, species, leaf faces and droplet volumes. Species were nested within sites, leaf faces within species, and droplet volumes within leaves (Holder, 2007; Rosado et al., 2010). Spearman rank correlation was used to verify the consistency in the species ranking across the different droplet volumes used to measure LWR and LWH. Small and non-significant coefficients indicate more changes in species ranking among the droplet volumes (Garnier et al., 2001; Rosado and de Mattos, 2007). Analysis of covariance (ANCOVA) was used to verify whether the relationship between LWR and LWH was affected by the water droplet volume, and Spearman correlation was used to test the relationship between leaf wetness traits and LWU. A one-sample t-test was used to determine if the increase in percentage LWU after the first submergence was significantly higher than 0 %. All statistical analyses were performed using the R environment (R Development Core Team, 2014) at a significance level of α = 0·05.

RESULTS

Leaf water retention and hydrophobicity differed significantly among sites, species, leaf faces and droplet volumes (Table 2; Supplementary Data Fig. S1, Tables S1 and S2). Leaf wetness trait values varied according to the droplet water volume used (Fig. 1). For LWR, there were no significant differences between droplets of 5 and 10 μL (Fig. 1A). These small droplets rarely dripped from the leaves, thus all species showed high retention values when these volumes were used (mean LWR for all species together: 5 μL droplet = 88·7°; 10 μL droplet = 86·5°). With an increase in the droplet volume, LWR decreased, reaching the minimum value for all species when measured with 50 μL droplets. LWH values were less variable among droplet volumes (Fig. 1B), and significant differences were found only for 15 μL droplets.

Fig. 1.
Variations in leaf water retention (LWR) (A) and hydrophobicity (LWH) (B), according to the droplet volume (5, 10, 15, 25 and 50 μL) considering the mean values ± s.d. for all 14 species tested. Letter codes indicate homogeneous ...
Table 2
Summary of results of the nested ANOVA for leaf water retention and leaf water hydrophobicity measurements using the following as nominal variables: sites (Atlantic rain forest and high-altitude grassland), species (seven common species from each site), ...

A drop-volume effect was also observed for species ranking (Fig. 2). A higher number of low and non-significant Spearman rank coefficients were found for LWR than for LWH (Table 3). ANCOVA results also showed that LWR values were significantly affected by the droplet volume (ANCOVA; F = 35·7, d.f. = 4, P < 0·001). The relationship between LWR and LWH was not significant for any of the droplet volumes tested (ANCOVA; F = 3·54, d.f. = 1, P = 0·06, Fig. 3).

Fig. 2.
Leaf water retention (LWR) (A) and hydrophobicity (LWH) (B) for each water droplet volume (5, 10, 15, 25 and 50 μL) for the 14 species analysed, seven from the Atlantic rain forest (Parque Nacional da Floresta da Tijuca) and seven from ...
Fig. 3.
Relationship between leaf water retention (LWR) and hydrophobicity (LWH) for each droplet volume (5, 10, 15, 25 and 50 μL) for 14 species from the Atlantic rain forest (Parque Nacional da Floresta da Tijuca) and the high-altitude grassland ...
Table 3
Spearman rank correlation coefficients comparing the ranking of 14 species (from Parque Nacional da Floresta da Tijuca, Atlantic rain forest; and Parque Nacional de Itatiaia, high-altitude grassland, both located in Rio de Janeiro, Brazil) in relation ...

All sampled species were able to perform LWU (Table 1). Nevertheless, the percentage increase in LWU varied among species, ranging from 9·6 % in Machaerina ensifolia to 60·1 % in Graphistylis itatiaiae. No significant relationships were found between percentage LWU and leaf wetness traits (Fig. 4) (Spearman rank correlations: LWR, ρ = –0·02, P = 0·94; LWH, ρ = –0·08, P = 0·77).

Fig. 4.
Relationship between leaf water retention (LWR) (A), leaf water hydrophobicity (LWH) (B) and leaf water uptake – percentage increase in leaf water content after leaf submergence in distilled water (LWU), for 14 species from the Atlantic rain forest ...

DISCUSSION

Changes in droplet volume significantly affected the measurement of leaf wetness traits, but LWR was more affected than LWH. Although previously unexplored for leaf surfaces, the drop-volume effect on retention and hydrophobicity properties has been a subject of many debates in material and chemistry sciences (e.g. Drelich et al., 1993; McHale et al., 2004; Vafaei and Podowski, 2005; Das and Das, 2010; Cansoy, 2014). Hence, before we can determine the functional meaning of leaf wetness traits, we must first attempt to understand the physical processes behind the drop-volume effect.

The drop-volume effect on leaf wetness traits

The hydrophobicity of any material (including leaves) is a property of the liquid–solid system and, at first, only depends on the balance between adhesive forces that favour spreading (acting between the liquid and the solid surfaces) and the counteracting cohesive forces (among liquid molecules) (Vafaei and Podowski, 2005; Lamour et al., 2010). This material-dependence principle, however, is valid only until a critical droplet volume is reached (Vafaei and Podowski, 2005). Thus, the contact angles will only be affected by the droplet volumes after this threshold has been exceeded. From this point forward, gravity starts deforming the droplet shape, and progressive increases in drop volume tend to reduce the contact angles (Drelich et al., 1993). Thus for large drops, the contact angle is governed by the liquid volume rather than by the solid surface traits (Vafaei and Podowski, 2005; Das and Das 2010).

For pure water, the critical droplet volume is about 10 μL. Therefore, droplets larger than 10 μL should not be used to measure contact angles (Cansoy, 2014). In fact, in our study, the drop-volume effect on LWH was detected after this threshold, i.e. significant differences in LWH were found for 15 μL droplets, but not for 5 or 10 μL droplets. However, the reason why only the 15 μL droplets, and not the 25 or 50 μL droplets, differed from the other volumes is not clear. This threshold may also explain why Schreiber (1996) did not find a significant drop-volume effect on LWH values, since, in his study, droplets only ranged from 1 to 10 μL. As most of the studies about leaf wetness have used droplets of 5 μL to measure LWH (Rosado and Holder, 2013), we propose that this value should be adopted as the standard to determine the contact angle on leaf surfaces, providing a safety margin to prevent a drop-volume effect on LWH measurements.

The detachment or sliding down of a droplet on an inclined surface also depends on the occurrence of a critical droplet volume because droplets only begin to move when the gravity forces are greater than the surface forces (Konrad et al., 2012). For most of our species, the critical volume was surpassed with 15 μL droplets, since the 5 and 10 μL droplets were rarely shed. Droplets of 50 μl, which simulate very large raindrops, have been used to measure LWR in the majority of the studies on this issue (Rosado and Holder, 2013). On the one hand, the use of 50 μl as a standard ensures that the critical volume will be exceeded for most species, but on the other hand, it brings, at least, two methodological problems. First, as mentioned above, for large drops, gravity might be more important than surface properties for determining the degree of droplet retention. Secondly, this trait becomes immeasurable in small-leaf species, on which droplets of 50 μL simply do not fit. A small leaf area is a common trait in plants subjected to abiotic stresses (cold, drought, heat and high radiation) (Cornelissen et al., 2003); thus, the impossibility of measuring LWR in these species makes it infeasible to compare leaf wettability along environmental gradients. These comparative studies are essential to gain an understanding of the degree of convergence among leaf wetness traits in similar habitats around the world, as well as for investigating their actual impact on ecohydrological processes (Brewer and Nuñez, 2007; Rosado and Holder, 2013).

As shown in this study, not only the absolute trait values, but also the species ranking varied depending on the droplet volume used to measure LWR and LWH. Therefore, studies that have used different droplet sizes are not comparable, which reinforces the need for a standard method in leaf wetness measurements. It is remarkable that classifications based on LWH were more repeatable among different droplet volumes than those based on LWR. The higher consistency in species ranking for hydrophobicity and the possibility of measuring this trait in smaller-leaf species (on which 5 μL droplets would fit) recommend the use of this functional trait to compare the ability of different species to retain or repel water, rather than the use of leaf water retention (LWR).

Relationship between LWR and LWH

Contrary to common expectations, a significant relationship between LWR and LWH was not found, regardless of the droplet volume used to determine these traits. It is intuitively expected that in highly non-wettable leaves (high LWH), water droplets should roll off more easily (low LWR). This negative correlation was corroborated in some studies (Brewer and Smith, 1997; Brewer and Nuñez, 2007), but not in others, where the opposite pattern was found (Pandey and Nagar, 2003; Holder, 2012). This highlights that the relationship between these traits is still a controversial issue in the literature.

It has been theoretically proposed (McHale et al., 2004), and then verified on synthetic surfaces (Pierce et al., 2008), that the adhesion of liquid drops to solids is not dictated by the static contact angles (hydrophobicity), but by the hysteresis contact angle. Hysteresis is defined as the difference between the maximum advancing contact angle (θmax) and the minimum receding contact angle (θmin) measured on a droplet immediately before it starts moving on a tilted plane. The smaller the contact angle hysteresis, the more easily a drop will roll off the surface (Krasovitski and Marmur, 2005). The hysteresis angles are largely influenced by the presence of chemical contaminations, solutes in the liquid or a previous film on the surface, and by the degree of surface heterogeneity (de Gennes, 1985), which, in leaves, is mostly created by cuticle wax structures and/or trichomes (Wagner et al., 2003). In leaves with low structural complexity and density of epidermal structures, the hysteresis is minimized, resulting in low leaf water retention (Konrad et al., 2012). Lower trichome density is also related to lower leaf hydrophobicity (Brewer et al., 1991). Therefore, the theoretically expected relationship is just the opposite of that in intuitive thoughts, and droplets should roll off more easily (low LWR) from the most wettable leaves (low LWH). Alternatively, the presence of dense trichome arrangements can simultaneously prevent the spread of water droplets and promote a higher adherence onto the leaf surface, resulting in high values for both traits (Brewer and Smith, 1994; Holder, 2012).

Implications of leaf wetness traits for leaf water uptake

The expected correlation between leaf wetness traits and LWU was not found. Thus, at least for the sub-set of species tested, hydrophobicity and retention cannot be used as proxies to predict the ability of a plant to perform LWU. In this study, LWU% was assessed through the submergence of the whole leaf in water, so it is reasonable to assume that leaf traits directly related to water absorption (such as the cuticle chemical composition and the presence of specialized epidermal structures) may be more important for determining foliar uptake than LWR and LWH, as demonstrated by Eller et al. (2013). If the leaf surface is not water permeable, neither a greater spreading nor a greater persistence of the water droplet on the leaf surface will ensure a higher water uptake. However, the absence of a relationship does not necessarily mean that leaf wetness traits should be precluded. Although labelled as ‘wetness trait’, the functional significance of LWH may be related to other environmental factors such as vapour pressure deficit, solar radiation or ice formation (Jordan et al., 2005; Koch et al., 2006; Aryal and Neuner, 2010; Rosado et al., 2010; Eller et al., 2013). In summary, our findings stress that the validation of LWR and LWH must be done before they can be used as proxies (Rosado et al. 2013), not only for LWU, but also for other ecophysiological processes commonly associated with leaf wettability, such as throughfall, gas exchanges, epiphyll colonization, pollution deposition, canopy interception and water storage.

Conclusion

Regardless of the environment, most plants are frequently subjected to leaf wetness events (Brewer, 1996). Therefore, a high selective pressure to retain or repel the water droplets on leaf surfaces may be an important, yet still rarely assessed, ecological process. Due to climate change, the frequency, intensity and duration of rain, fog, dew and drought events are likely to be altered worldwide (Collins et al., 2013). How these changes will affect leaf wetness traits, and thus plant water-use strategies, is an interesting question that remains to be elucidated. Although LWH and LWR are commonly linked to several ecophysiological processes (from the leaf to the ecosystem level), few studies have assessed the actual significance of these two functional traits at local, regional and global scales, which impairs the ability to predict plant responses to changes in water availability. Before the validation of a trait for predicting a given process (e.g. LWU) and for properly comparing leaf wetness traits among different species, it is imperative to standardize the methodological approach used to measure these traits and to identify their functional roles. This study clearly showed that water droplet volume does matter when measuring leaf wetness traits. Not only the absolute values, but also the species ranking, were affected by changes in droplet volume. We suggest a standard 5 μL droplet to measure LWH and a 50 μL droplet to determine LWR, although a 50 μL droplet is not feasible for small-leaf species, and LWR is less consistent than LWH.

SUPPLEMENTARY DATA

Supplementary data are available online at www.aob.oxfordjournals.org and consist of the following. Figure S1: differences in leaf water hydrophobicity (LWH) and retention (LWR) among the two studied sites: Atlantic Rain Forest and High Altitude Grassland, RJ, Brazil. Table S1: mean ± s.d. leaf water retention (LWR) values for 14 species from the Atlantic Rain Forest and the High Altitude Grassland, RJ, Brazil. Table S2: mean ± s.d. leaf water hydrophobicity (LWH) values for 14 species from the Atlantic Rain Forest and the High Altitude Grassland, RJ, Brazil.

Supplementary Data:

ACKNOWLEDGEMENTS

This paper derived from I.S. Matos’ PhD thesis. We are grateful to Walquíria Felipe and Yan Moraes for their help on field work and laboratory measurements. We also thank Professor Carlos F. D. Rocha, Laboratório de Ecologia Vegetal team and Artigo Científico class for comments and suggestions on the first draft of this manuscript and CAPES for scholarship for the first author. SISBIO 48911-1/SISBIO 46004-2.

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