Introduction

The Atlantic Forest is considered a biome of great extension and biodiversity, with an original area of approximately 1.315.460 km2 (SOS Mata Atlântica 2019–2020), which extends from Rio Grande do Norte to Rio Grande do Sul (Murray-Smith et al. 2009). It is the second largest tropical rainforest in the world, being one of the most important biogeographical domains in South America, covering about 8% of all world biodiversity (Ribeiro et al. 2009; Magnago et al. 2015).

It is currently classified as a priority region for conservation and one of the main biodiversity hotspots in the world (Myers et al. 2000; Rezende et al. 2018). Furthermore, Béllard et al. (2014) reported the biome is one of the three most vulnerable hotspots to landscape changes, such as climate change, invasive species, and urbanization. This is because the species in the biome are more vulnerable to extinction due to a decrease in habitat from anthropic actions or extreme weather events (Urban 2015). The accelerated deforestation of the Atlantic Forest threatens a distinct and exclusive biological wealth that promotes the diversity of phytophysiognomies associated with the biome, such as sandbanks (Scarano and Ceotto 2015). Formed about 10,000 years ago (Holocene) as a result of sea regression processes and/or by river and lake sedimentary depositions in coastal plains (Silva 1999), the Brazilian sandbanks harbor species from neighboring ecosystems of the Atlantic Forest and other biomes (e.g., Cerrado and Caatinga).

Sandbanks have severe environmental filters, for example, high temperatures and irradiance, water and nutritional deficit, and high salinity levels. The high incidence of winds and salt spray deposition are also observed, as factors present in coastal ecosystems (Melo Jr. and Boeger 2018; Silva et al. 2020), which can affect plant fitness over time. Specifically, the sandbanks in the north of the state of Rio de Janeiro have four vegetation types: sandbanks forest (shaded environment, where the plants are larger and the soil has a greater amount of organic matter), Clusia formation (dense thickets with the species Clusia hilariana in the central region, generating intermediate shading), beach grass and shrub formation (small thickets due to the high effect of irradiance, where the soil is extremely poor) and the beach grass formation (inhabited by creeping and herbaceous plants, the irradiance is high, and the effects of wind, sea air, and salinity make this region highly selective for plant species) (Arruda et al. 2009; Assumpção and Nascimento 2000). The microclimatic and edaphic differences between the vegetation types lead to a vegetation gradient that increases as one moves away from the sea. For the species to acclimatize to these formations, it is necessary to adjust their morphological and anatomical leaf attributes (Cerqueira 2000; Scarano 2002; Melo Jr. and Boeger 2016).

Understanding how leaf morphological and anatomical attributes vary along environmental gradients is essential to clarify how selective processes act in different species (Reich et al. 1992; Rozendaal et al. 2006; Rossatto & Kolb 2013). In addition, it is important to understand the ecological strategies plants adopt. For example, it is possible to evaluate the variation in leaf structure to optimize photosynthetic processes and decrease water loss to the environment, reflecting on the control of niche segregation and changes in floristic composition and species distribution (Oliveira et al. 2018; Esquivel-Muelbert et al. 2019).

In this context, the permanence of species in resource-poor environments directly depends on the functional attributes that make them adapted to local environmental filters (Sultan 2000; Wright et al. 2004; Araújo et al. 2022). The leaf is the most studied organ to understand these processes since it responds quickly to environmental variations and is considered highly plastic (Simioni et al. 2017; Pireda et al. 2019; 2020; Araújo et al. 2021; Ariano et al. 2022; Borges et al. 2022). In addition, in xeromorphic environments, plants tend to produce leaves with smaller leaf area and greater stomatal density, thereby reducing water loss to the atmosphere; increase the thickness of the palisade parenchyma layers to increase the photosynthetic capacity; invest in thickening the cuticle to minimize the loss of water to the environment; and increase leaf thickness to improve water storage and equal distribution of light by the mesophyll (Melo Jr. and Boeger 2018; Pireda et al. 2019) making leaves more resistant to water stress, high irradiance, salinity, and nutritional poverty (Niinemets 2001; Arruda et al. 2009; Amorim and Melo Junior 2017; Cabral et al. 2018). Some herbaceous species, to overcome the environment variables present in the sandbanks, end up investing in structures such as aquiferous parenchyma, Kranz sheath, bulliform cells, and isobilateral mesophyll, aiming at greater storage with less water loss, more efficient gas exchange, and light capture (Arruda et al. 2009; Viana et al. 2021). In this way, various combinations of leaf morphoanatomical attributes are shaped by different environmental factors and result in different forms of tolerance to drought and high irradiance.

Therefore, our study compares and characterizes the leaf morphoanatomical attributes of dominant species that occur in different vegetation types (sandbanks forest formation, Clusia formation, beach grass and shrub formation, and beach grass formation) in a sandbanks ecosystem of the Atlantic Forest. This study involves understanding plant-environment relationships, especially the consolidation processes of sandbanks vegetation and the possibility of predicting changes in the community due to future climate changes. In addition, it provides relevant information related to restructuring, conserving, and maintaining ecosystem services.

For this, we asked the questions below.

  1. 1)

    Do leaf traits converge between species sharing the same habitat? We expected to find convergent leaf attributes within the vegetation types. Specifically, we expected the vegetation types furthest from the sea line (sandbanks forest formation and Clusia formation) to have characteristics related to less water loss to the atmosphere. On the other hand, we expected that the vegetation types closer to the sea line (beach grass and shrub formation and beach grass formation) to have characteristics related to greater water storage (Bächtold and Melo Júnior 2015; Amorim and Melo Júnior 2017; Pireda et al. 2019, 2020).

  2. 2)

    Are the leaf traits of the dominant species different between each vegetation type? The vegetation types present a wide variability in leaf characteristics, regardless of floristic composition. Those far from the sea line were expected to have crystals and secretory structures, and lower values for leaf area and specific leaf mass, since they are subjected to high temperatures and greater vapor pressure deficit (Campbell et al. 2018; Bezerra et al. 2020; Pessoa et al. 2019, 2021). On the other hand, the vegetation types closer to the sea line were expected to have epicuticular wax, thick and striated cuticles, and high leaf water content, since they are exposed to high irradiance and higher air humidity (Arruda et al. 2009; Melo Jr. and Boeger 2018; Pireda et al. 2019, 2020).

  3. 3)

    What is more important in defining leaf traits, the species' taxonomy, or the habitat it occupies? Vegetation is likely to be more important in explaining most of the variability of the leaf characteristics in this sandbanks system than taxonomic differences, since the vegetation types are subject to different environmental conditions (Araújo et al. 2021; Emilio et al. 2021).

Materials and methods

Study area

The study was carried out in the Fazenda Caruara RPPN, in the Grussaí/Iquipari Lagoon Complex (GILC) in the municipality of São João da Barra, in northern Rio de Janeiro State (21º 72 65 4`S and 41º 03 64 5`W). It is the most prominent private sandbanks reserve in Brazil with around 4.235 hectares. The region's climate has a marked seasonality, with a rainy summer (December to March) and a dry winter (June to September), with an average annual rainfall of 1.000 mm and an average annual temperature ranging from 19 to 25 °C (Assumpção and Nascimento 2000). Its climate is type Aw according to the Koppen classification (Koppen 1948; Alvares et al. 2014).

The Fazenda Caruara RPPN has four sandbanks vegetation types: sandbanks forest formation, Clusia formation, beach grass and shrub formation, and beach grass formation. We carried out the study along a vegetation gradient of these types (Figs. 1, 2; Table 1; Assumpção and Nascimento 2000). The sandbanks forest formation has 45 to 60% tree cover and an upper canopy 2 to 15 m tall. In this formation, the thickets become denser, forming a continuous forest with litter. It is located 980 m from the sea line (Fig. 1A; Assumpção and Nascimento 2000). The Clusia formation has an upper canopy that is 1 to 3 m tall, and Clusia hilariana enriches the soil with its leaves, which allows other species to colonize around it (Villela et al. 2020). This formation is 580 m from the sea line (Fig. 1B; Assumpção and Nascimento 2000). The beach grass and shrub formation has a canopy that is 1 m tall, and nucleation occurs where cacti and bromeliads help other plant species to become established. This formation is 250 m from the sea line (Fig. 1C; Assumpção and Nascimento 2000). The beach grass formation comprises short and herbaceous plants subjected to variations in the sea level and consequent to the salinity and strong wind effects (Fig. 1D; Assumpção and Nascimento 2000).

Fig. 1
figure 1

Sandbanks vegetation types, in Rio de Janeiro, Brazil, South America. A Sandbanks forest, B Clusia formation, C Beach grass and shrub formation and D Beach grass formation. The blue zone indicates the current distribution of the Atlantic Forest in Brazil. The green dots indicate the distribution of vegetation types: sandbank forest (980m from the tide line), Clusia formation (580m), beach grass and shrub (250m) and beach grass formation (tidal line).

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Fig. 2
figure 2

Microclimatic differences in the sandbanks vegetation types. a Temperature; b irradiance; c vapor pressure deficit (VPD); d air humidity. All measurements were taken monthly at noon, for a period of one year. The values were obtained through measurements around the individuals, where an average per individual and a general average were performed for each measurement taken during the month. Different lowercase letters denote significant differences (Tukey, P < 0.05).

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Table 1 Characterization and life habits of the species in the different types of restinga vegetation
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Species selection and data collection

To find the variation in leaf attributes, we selected dominant species based on species number, relative frequency, and importance values index for each vegetation type (Assumpção and Nascimento 2000). Thus, in sandbanks forest formation, four species were selected: Protium heptaphyllum (Aubl.) Marchand (Burseraceae), Cynophalla flexuosa (L.) J. Presl (Capparaceae), Sideroxylon obtusifolium (Roem. & Schult.) T.D.Penn (Sapotaceae), and Scutia arenicola (Casar.) Reissek (Rhamnaceae). In the Clusia formation, three species were selected: Clusia hilariana Schltdl. (Clusiaceae), Inga maritima Benth (Fabaceae), and Pera glabrata (Schott) Baill. (Peraceae). In the beach grass and shrub formation, three species were also selected: Schinus terebinthifolia Raddi (Anacardiaceae), Eugenia uniflora L. (Myrtaceae), and Varronia curassavica Jacq. (Boraginaceae). Finally, two species were selected in beach grass formation: Ipomoea imperati (Vahl.) Griseb. (Convolvulaceae) and Blutaparon portulacoides (A.St.-Hil.) Mears (Amaranthaceae). Table 1 presents all selected species, their common name, life habits, whether they are endemic or not, distribution among Brazilian phytogeography domains and conservation status.

To determine leaf morphological and anatomical characteristics, we randomly selected 25 leaves from each species (five leaves per individual) that were the following: 1) fully expanded; 2) in full sun; and 3) free from damage caused by pathogens and/or herbivores. This was done in July and September 2019. Additional details on species characteristics are in Table 1.

Measurements of microclimatic parameters

To measure temperature, humidity and irradiance, a LI-250 radiometer and a thermo-hygroanemometer (AKSO–AK832) were used. Measurements at four different points around each individual in each vegetation type were taken at an average distance of 3 m from one end to the other. All individual plants (n = 20 of each species) were visited at predefined times throughout the day (12:00 to 14:00). Each month, measurements were taken from a different end, one month at the sea line and the following month in the sandbanks forest region.

Later we calculated the vapor pressure deficit (VPD) from the formula: es/ea, where es: saturated vapor pressure of the air and ea: vapor pressure of the air.

es:0.61137 * EXP ((17.502 * Temperature) / (Temperature + 240.97)).

ea: 1—(Humidity / 100).

All measured microclimate variables are shown in Fig. 2.

Morphoanatomical characterization

The leaf attributes evaluated in this study are listed in Table 2. For the leaf area analysis, five expanded leaves were collected from each individual of each species (N = 25). The leaves were scanned, and the area was measured using the software ImageJ, according to Rasband (1997–2008) and Perez-Harguindeguy et al. (2013). To determine the thickness, leaf water content and leaf mass area, 0.4-cm leaf discs were removed from five expanded leaves per individual. The discs were hydrated in distilled water for 24 h, and the saturated mass was measured using a digital scale (Shimadzu model AY220, Japan). In addition, a digital caliper (Stainless Hardened, Switzerland) was used to measure the thickness of the leaves. The hydrated disks were placed in an oven at 60 ºC for 72 h to measure the dry mass. The leaf water content (LWMC) was calculated as the difference between saturated mass and dry mass (Perez-Harguindeguy et al. 2013). The leaf mass area (LMA) was calculated by dividing the dry mass by the disc area (Kluge and Ting 1978).

Table 2 Leaf morphological and anatomical attributes evaluated for species in different sandbanks vegetation types
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For the stomatal density, 25 leaves per species were selected. The epidermis was dissociated using the Franklin method (1945), where the samples were placed in a solution (1:1) of acetic acid and hydrogen peroxide. Subsequently, semipermanent slides were mounted and observed under a light microscope (Axioplan, ZEISS, Germany) coupled to a camera (Moticam Pro 282B, Hong Kong).

The number counts of the stomata per mm2 were performed on semipermanent slides with the choice of 25 random fields with the ImageJ software. Twenty-five leaves of each species were analyzed, and the thickness of the epidermis, cuticle, palisade and spongy parenchyma was measured with the same software (Rasband, 1997–2008; Perez-Harguindeguy et al. 2013).

Sample preparation for anatomical analysis

Three leaves of each species were selected for light microscopy. First, the middle third fragments were fixed in a solution of 2.5% glutaraldehyde, 4% formaldehyde and a 0.05 M sodium cacodylate buffer at pH 7.2 (Karnovsky 1965, modified by Da Cunha et al. 2000). Subsequently, the samples were post-fixed in 1% osmium tetroxide and a 0.05 M sodium cacodylate buffer for two hours in the dark. Then, the samples were dehydrated in a keto series and embedded in epoxy resin (Epon®). Semi-thin sections (70 nm) were made using a Reichert Ultracuts Leica Instruments® ultramicrotome and then stained with 1% toluidine blue and 1% borax buffer (Johansen 1940).

Freehand cross sections were made of the midrib, petiole and leaf blade for all species, which were stained with Astra blue and basic fuchsin. Subsequently, semipermanent slides were mounted with 50% glycerin (Johansen 1940; Kraus et al. 1998). In addition, images were taken with a camera (Moticam Pro 282B, Hong Kong) coupled to a light microscope (Axioplan, ZEISS, Germany). The images were used for the qualitative descriptions and quantitative analyses using the software ImageJ (Rasband 1997–2008; Perez-Harguindeguy et al. 2013).

Sample preparation for the micromorphological analysis

After fixing and dehydrating the material for light microscopy, part of the samples were critical-point-dried (CPD 030, Baltec) with CO2, adhered to stubs with carbon tape and coated with a thin layer (± 20 nm) of palladium gold (SCD 050, Baltec, Switzerland). Then, images were taken with a scanning electron microscope (EVO 40, ZEISS, Germany) using a voltage of 15 kV.

Statistical analysis

To test the first hypothesis, a matrix was prepared that included the anatomical and morphological leaf variables (Table S2) obtained for each sample unit (species). Then, a two-factor cluster analysis was performed (species and anatomical variables) using the UPGMA algorithm and the Sørensen similarity coefficient, considering Jaccard distances (Lance and Williams 1967; Ferreira 2008). To test the second hypothesis, the leaf characteristics of the species were compared between the vegetations using a two-way ANOVA (with species and vegetation as predictors). Subsequently, post hoc Tukey tests were used to test the differences in leaf characteristics of each species between the vegetations, with the individuals as the sample unit.

To test the third hypothesis, a variance partition was created to better understand the importance of taxonomic (species) versus environmental (vegetation) controls in the variation of leaf traits. Multilevel linear mixed models were constructed for each leaf trait measured, with vegetation and species as nested random factors, following the approach used in Rosas et al. (2019) and Araújo et al. (2021). Normality and homogeneity of variance were verified using the Shapiro–Wilk and Levene tests, respectively (Levene 1961; Shapiro–Wilk 1965). When necessary, the variables were transformed into log10 for normality assumptions. All analyses were performed using the software R version 4.1.0v (R Core Team 2022).

Results

Convergent and divergent leaf characteristics

The dendrogram shows four large groups (Fig. 3). The first group is formed exclusively by the beach grass formation (I. imperati and B. portulacoides) that has thick and straight epidermal cell walls (Figure S1), a thick striated cuticle (Fig. 4d; S1), crystals (Fig. 4b, c, 4f; S2) and epicuticular wax on both sides (Figure S1). The second group is made up of only V. curassavica in the beach grass and shrub formation, which has characteristics such as dorsiventral mesophyll (Fig. 4 g), a thick cuticle (Fig. 4 h and S1s), stomatal crypts (Fig. 4i; S2), crystals and trichomes (Fig. 4 g, S1; S2; S3), a papillose adaxial surface (Fig. 4j) and epicuticular wax (Figure S1). The third group comprises species from the Clusia formation (I. maritima and P. glabrata) and sandbanks forest (C. flexuosa and P. heptaphyllum), which share a hypostomatic leaf (Fig. 4 m; S1; S2), few layers of palisade and spongy parenchyma (Figure S2), a collateral bundle surrounded by perivascular fibers (Fig. 4 k; S3), a striated cuticle (Fig. 4 l; S1) and the presence of trichomes and associated microorganisms (Figure S1). Finally, the fourth group has species from the beach grass and shrub formation (S. terebinthifolia and E. uniflora), Clusia formation (C. hilariana) and sandbanks forest formation (S. arenicola and S. obtusifolium), which have small epidermal cells (Fig. 4n, 4o; S1) a petiole with a plano-convex contour (Figure S3), a striated cuticle (Fig. 4o; S1) and an abundance of crystals (Fig. 4p; S2).

Fig. 3
figure 3

Similarity dendrogram (UPGMA) between 12 species of different vegetation types of sandbanks, generated by a matrix of presence and absence of anatomical characteristics. Abbreviations: Strai. Epi: Straight wall epidermal cells; Sinu. Epi: Sinuous wall epidermal cells; Thic. Epi: Thick-walled epidermal cells; Smal. Epi: Small epidermal cells; Larg. Epi: Large epidermal cells; Hyp. Leaf: Hypostomatic leaf; Amp. Leaf: Amphistomatic leaf; Epi. Leaf: Epistomatic Leaf; Dors. Mes: Dorsiventral mesophyll Isob. Mes: Isobilateral mesophyll; Unis. Epi: Uniseriate epidermis; Thic. Cut: Thick cuticle; Strai. Per: Straight periclinal wall; Conv. Per: Convex periclinal wall; Stom. Cryp: Stomatal crypt; Sub. Lay: Subepidermal layer; Scler. Shea: Sclerenchymatic sheath; Kranz. Shea: Kranz sheath; Palis -: One to three layers of palisade parenchyma; Palis +: Four to six layers of palisade parenchyma; Spong -: One to five layers of spongy parenchyma; Spong +: Six to twelve layers of spongy parenchyma; Aqui. Par: Aquiferous parenchyma; LB. Du or Cav: Ducts and/or cavities; LB. Cryst: Presence of crystals on the leaf blade; LB. Tric: Trichomes on the leaf blade; Par. Stom: Paracytic stomata; Ano. Stom: Anomocytic stomata; Acti. Stom: Actinocytic stomata; Mid. Pla-conv. Cont: Plano-convex contour; Mid. Con-con. Cont: Concave-convex contour; Mid. Bic. Cont: Biconvex contour; Mid. Flat. Cont: Straight contour; Mid. Ang. Col: Angular collenchyma; Mid. Ring. Col: Annular collenchyma; Mid. Lac. Col: Lacunar collenchyma; Mid. Col. Abs: Collenchyma absent; Mid. Col. VB: Collateral vascular bundle; Mid. Bic. VB: Bicollateral vascular bundle; Mid. Cont. Palis: Continuity of the palisade parenchyma in the rib; Mid. Bul. Cel: Bulliform cells; Mid. Du or Cav: Ducts and/or cavities in the rib; Mid. Latic: Laticifers; Mid. Periv. Fib: perivascular fibers; Mid. Cryst: Crystals present in the rib; Mid. Tric: Trichomes present on the rib; Wit. Pet: Petiole absent; Pet. Pla-conv. Cont: Plano-convex contour of petiole; Pet. Con-com. Cont: Concave-convex contour of petiole; Pet. Bic. Cont: Biconvex contour of petiole; Pet. Flat. Cont: Straight contour of petiole; Pet. Ang. Col: Petiole angular collenchyma; Pet. Ring. Col: Petiole annular collenchyma; Pet. Lac. Col: Petiole lacunar collenchyma; Pet. Col. Abs: Petiole collenchyma absent; Pet. Col. VB: Collateral vascular bundle of the petiole; Pet. Bic. VB: Bilateral petiole vascular bundle; Pet. Cont. VB: Continuity of the vascular system of the petiole; Pet. Bul. Cel: Bulliform cells; Pet. Du or Cav: Petiole ducts and/or cavities; Pet. Latic: Laticifers; Pet. Periv. Fib: Perivascular fibers of the petiole; Pet. Cryst: Presence of crystals on the petiole; Pet. Tric: Presence of trichomes on the petiole; Epic. Ada: Presence of epicuticular wax on the adaxial surface of the leaf blade; Epic. Bot. Sid: Presence of epicuticular wax on both surfaces of the leaf blade; Wit. Epic: Without wax; Stom. Epic: Presence of epicuticular wax around stomata; EPP. Ornam: Presence of cuticle ornamentation around stomata; Stri. Aba: Striated cuticle on abaxial surface; Stri. Ada: Striated cuticle on adaxial surface; Pap. Ada: Papillose surface; Bact or Fung: Fungi and bacteria; MM. Tric: Trichomes.

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Fig. 4
figure 4

Anatomical images of species in the sandbanks vegetation types. a Dorsiventral mesophyll of B. portulacoides in the beach grass formation; b Kranz sheath of B. portulacoides in the beach grass formation (shown by white arrows); c Isobilateral mesophyll of I. imperati in the beach grass formation; d Aquiferous parenchyma of B. portulacoides in the beach grass formation; e Aquiferous parenchyma of I. imperati; f Bulliform and laticifer cells in the petiole of I. imperati in the beach grass formation (shown by white arrows); g Tector and glandular trichomes of V. curassavica in the beach grass and shrub formation (shown by white arrows); h Epidermal cell secretory in V. curassavica in the beach grass and shrub formation; i Trichomes on the abaxial surface of V. curassavica in the beach grass and shrub formation; j Papillose adaxial epidermis of V. curassavica in the beach grass and shrub formation (shown by white arrows); k Secretory cavity in the vein of P. heptaphyllum in the sandbanks forest formation (shown by white arrows); l Striated cuticle and wax on the adaxial surface of C. flexuosa in the sandbanks forest formation (shown by white arrows); m Sclerenchymatic sheath in P. heptaphyllum in the sandbanks forest formation (shown by white arrows); n Amphistomatic leaf (adaxial surface) of S. arenicola in the sandbanks forest formation; o Cuticle ornamentation around the stomata in S. obtusifolium in the sandbanks forest formation (shown by white arrows); p Petiole with collateral bundle in E. uniflora in the beach grass and shrub formation (shown by white arrows). Bars: 200µm: a; 100µm: b, c, f, g, m, p; 50µm: d, e; 20µm: h, i, j, k, n, o; 10µm: l

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There is a similarity between the sandbanks forest, Clusia, and beach grass and shrub formations. However, the beach grass formation is separated from the other vegetation types due to the unique characteristics of its species, such as aquiferous parenchyma (Fig. 4c and 4d), a Kranz sheath (Fig. 4a, b), bulliform cells (Fig. 4f), epistomatic leaf (Figure S1m) and isobilateral mesophyll (Fig. 4c). In addition, the aquiferous parenchyma (Fig. 4e), bulliform cells (Fig. 4f), stomatal crypts (Fig. 4i), striated and thick cuticle (Fig. 4 l and 4o), the presence of crystals (Fig. 4 g), microorganisms (Fig. 4 l) and isobilateral mesophyll (Fig. 4c) are the main leaf attributes that separate the communities (Fig. 4 and Table S1).

Variation in leaf morphoanatomical attributes between vegetation types

Most leaf morphoanatomical attributes exhibited differences between vegetation types (Fig. 5). The leaf area showed no differences between the sandbanks forest and formation of Clusia. However, both were different from the beach grass and shrub formations and the beach grass formation (Fig. 5a; Table S2). For leaf thickness, there was a difference between the Clusia and beach grass formations, but no difference between the sandbanks forest and beach grass and shrub formations (Fig. 5b; Table S2). For leaf water content, there was no difference between the sandbanks forest, Clusia, and beach grass and shrub formations; however, all these differed from the beach grass formation (Fig. 5c; Table S2). For specific leaf mass and thickness of the spongy parenchyma, there were no differences between the sandbanks forest, beach grass and shrub formation and beach grass formation, but there was a difference in the Clusia formation (Fig. 5d, l; Table S2). For stomatal density, no differences were observed between the sandbanks forest and beach grass and shrub formations; there were only differences for the Clusia and beach grass formations (Fig. 5e; Table S2).

Fig. 5
figure 5

Leaf morphological and anatomical attributes of species in the sandbanks vegetation types. a Leaf area; b leaf thickness; c leaf water mass content; d leaf mass area; e stomatal density; f stomatal area; g abaxial cuticle thickness; h adaxial cuticle thickness; i abaxial epidermis thickness; j adaxial epidermis thickness; k palisade parenchyma thickness; l spongy parenchyma thickness. The points in the graphs represent the average of each individual per species. The different sizes of the dots reflect the values of the leaf attributes, where smaller dots represent lower values and larger dots represent higher values. Different lowercase letters denote significant differences (Tukey, P < 0.05).

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For stomatal area and the abaxial epidermis, there were no differences between the sandbanks forest, Clusia and beach grass and shrub formations; the beach grass formation differed from the others (Figs. 5f, i; Table S2). For the adaxial and abaxial cuticles, the beach grass and shrub formation species differed from the species in the other formations; there were no differences between the latter species (Fig. 5 g, h; Table S2). There was a difference between the Clusia and beach grass formations for adaxial epidermis and palisade parenchyma thickness (Fig. 5j, k; Table S2).

Variability of leaf morphoanatomical characteristics

To separate the effects of vegetation versus species on leaf traits, we performed a partition of variance analysis. The proportion of global variance accounted for by species versus vegetation varied according to the specific characteristic considered (Table S3). “Species” explained a high percentage of variance (53–90%) for leaf traits, including specific leaf mass, leaf area, leaf thickness, and palisade and spongy parenchyma thickness (Fig. 6). Variables related to stomata (e.g., stomatal density) and leaf mesophyll characteristics (e.g., epidermis thickness) were highly associated with vegetation (> 60% of the explained variance) (Fig. 6; Table S3).

Fig. 6
figure 6

Source of variation of leaf characteristics in the sandbanks vegetation types. Decomposition of variance at different ecological scales in vegetation levels (green bars), species (orange bars) and within (residual error, purple) for stomatal density (STD), stomatal area (STA), leaf area (LEA), leaf thickness (LET), leaf mass area (LMA), leaf water mass content (LWMC), palisade parenchyma thickness (PPT), spongy parenchyma thickness (SPT), adaxial epidermis thickness (ADET), abaxial epidermis thickness (ABET), adaxial cuticle thickness (ADCT), abaxial cuticle thickness (ABCT).

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Discussion

In this study, a similarity was observed between the sandbanks forest, Clusia, and beach grass and shrub formations, which may be related to the short distances between the vegetation types and/or being exposed to similar microclimatic conditions. Characteristics such as epidermal cells with straight and thick walls, hypostomatic leaf and thick and striated cuticle helped the species acclimate to the high irradiance conditions of these formations. On the other hand, the beach grass formation was separate from the others since this vegetation type is composed of species with exclusive characteristics (e.g., aquiferous parenchyma and a Kranz sheath), facilitating their development in this environment.

Several attributes appear along the vegetation types, which are plant characteristics found in dry environments, for example, epidermal cells with straight and thick walls, a hypostomatic leaf, a thick and striated cuticle, convex periclinal walls, crystals, trichomes, epicuticular wax, and collateral vascular tissue surrounded by perivascular fibers. The straight walls of the epidermal cells, striated cuticle, and epicuticular wax help reflect light and prevent the mesophyll from heating up because they form a reflective leaf surface (Melo Jr. and Boeger 2018; Ariano et al. 2022). The formation of this reflective surface becomes important for sandbanks plants since a mesophyll receiving an excess of light can cause the degradation of chlorophyll molecules, impairing the capture of light by the antenna complexes and the entire photosynthetic process (Demmig-Adams and Adams 1996).

Crystals act as calcium deposits in various regions of the leaf, such as the mesophyll, veins and petiole (Bezerra et al. 2020). Furthermore, the ubiquity of calcium crystals in sandbanks plants may represent an important strategy to reduce water loss, avoid photoinhibition and resist drought conditions (Garvie 2006; Brown et al. 2013). Plants from arid environments such as sandbanks can invest in the nocturnal construction of calcium crystals, mainly calcium oxalate crystals, to act as subsidiary diurnal sources of CO2 that will help the overall photosynthetic performance of the plant independently of the CO2 atmospheric availability (Tooulakou et al. 2016a). Generally, this mobilization of CO2 from calcium crystals occurs when the plants have their stomata closed to avoid water loss and when there is a mismatch between light reactions and CO2 fixation (Tooulakou et al. 2016b). In general, calcium crystals support a low photosynthetic rate (± 3 mmol of CO2 m−2.s−1 for 4 to 5 h) aimed only at the maintenance and survival of plants in arid environments and not the growth itself (Tooulakou et al. 2019). This mechanism may explain the large number of calcium crystals found in most species studied in the different types of sandbank vegetation.

Trichomes, in turn, can be tector or glandular and are common in several plant species; both help to protect against herbivory and store substances (Silva et al. 2020). In general, glandular trichomes may present phenolic compounds with secretion components (Ventrella et al. 2008), while in tector trichomes the phenolic compounds may be anchored to cell walls through covalent bonds (Karabourniotis et al. 2020). The phenolic compounds present in trichomes can act as protective filters against the action of UV-B radiation, preventing overheating of protoplasts and damage to proteins, lipidic and nucleic acids (Kulbat 2016; Csepregi and Hideg 2018). Glandular trichomes can also have mucilage inside, which characterizes an important strategy for tolerance to dry environments, since the mucilage has water chelating properties (Nguimbou et al. 2014; Ballego-Campos et al. 2020). In addition, tector trichomes can also establish reflective surfaces at high irradiance and establish a humid microclimate on the leaf surface, reducing the difference in leaf-air vapor pressure deficit and consequently reducing water loss by transpiration to the environment (Santos et al. 2016; Pessoa et al. 2019). According to Cabral et al. (2018), some of these characteristics may be determinants for colonization in different sandbanks communities.

On the other hand, divergent leaf characteristics, such as aquiferous parenchyma, a Kranz sheath, bulliform cells, and isobilateral mesophyll, demonstrate why the beach grass formation is separate from the other formations. The beach grass formation is distinct, with high irradiance, high air humidity, higher incidence of wind and high salinity. The greater instability in this formation resulted in it being separate from the others (Assumpção and Nascimento 2000). For example, Arruda et al. (2009) identified several foliar strategies in a creeping community in the sandbanks, such as a Kranz sheath, which increases carbon uptake in hot and dry environments, and isobilateral mesophyll, which more efficiently directs light through the palisade, decreasing photoinhibition damage. Furthermore, Viana et al. (2021) describe stomata on both leaf surfaces as a way of surviving in a dry environment, since this reduces the time stomata remain open, which prevents evapotranspiration. According to Arruda et al. (2009), these characteristics are relevant to increase leaf longevity, photosynthetic efficiency and water savings. In this way, the environmental variables on the sea line lead the beach grass formation to develop characteristics that diverge from those in the other formations.

The separation of the beach grass formation from the sandbanks forest, Clusia, and beach grass and shrub formations was also due to differences between the morphoanatomical attributes. Leaf area is generally smaller in environments with high irradiance since the plant avoids water loss (Melo Jr. and Boeger 2016). This attribute was previously analyzed in different sandbanks vegetation types, and individuals in the forest region had leaves with a greater leaf area (Melo Júnior et al. 2019). For example, Pireda et al. (2019) found smaller leaves in a sandbanks environment compared to a forest area. However, the beach grass formation had the leaves with the largest leaf area. This is possibly due to the leaves investing in N2 since this nutrient is scarce in sandbanks soils. A plant can also invest in leaf area to produce proteins and optimize its photosynthetic capacity (Rêgo et al. 2013). According to Wright et al (2004), an investment in photosynthetic proteins may be important in this formation, to increase carbon assimilation. Since the beach grass formation has higher humidity and lower temperature values, and vapor pressure deficit (VPD), the investment in the leaf area was beneficial and did not generate excess water loss.

The beach grass community also showed greater leaf thickness, which is due to a greater number of layers of palisade and spongy parenchyma in the mesophyll, favoring light absorption and gas exchange, making photosynthetic processes more efficient (Simioni et al. 2017; Pireda et al. 2019). The presence of a mesophyll with a palisade on both faces (isobilateral) was decisive in this formation (Arruda et al. 2009). For example, Melo Junior et al. (2019) associate thicker leaves with high exposure to irradiance. According to Pireda et al. (2019), a greater thickening of the spongy parenchyma can function as a true mirror chamber for light, directing it to the chloroplasts present in the palisade parenchyma.

The epidermis and cuticle are also associated with thickness; we observe a thick cuticle in all types of vegetation, which in turn is formed by lipid substances that reduce cuticular transpiration and protect against the action of winds and fungi (Turner 1994; Simioni et al. 2017). The epidermal cells may vary according to the light intensity (Rôças et al. 2001). Dickison (2000) reports that thicker epidermal cells can decrease leaf temperature, causing photosynthetic processes without showing photoinhibition. And according to Kozlwoski (1997), the epidermal cells and cuticles of plants that live in an environment with salinity are very thick.

The water content in the leaf was an important attribute, since one of the strategies used by the beach grass formation is storing water in tissues. According to Pireda et al. (2019), thick leaves also become succulent to overcome the difficulties imposed by the dry environment. Arruda et al. (2009) also found the presence of aquifer parenchyma and revealed how the plant overcame water scarcity (Viana et al. 2021). The specific leaf mass corresponds to the carbon expenditure in the construction of leaves (John et al. 2017). Generally, leaves with a high specific leaf mass are rigid, scleromorphic, and unpalatable to herbivores because there is a greater investment in carbon than in nitrogen during leaf formation (Wright et al. 2004). Sandbanks formations may have used a strategy on the leaf surface to avoid insect and microorganism attacks.

Contrary to expectations, taxonomic identity is the factor that most controls the variation of leaf morphological and anatomical attributes in the sandbanks vegetation types, such as leaf area, specific leaf mass, and adaxial and abaxial cuticles. This variation may be related to competition for resources and limitations in the availability of water (Araújo et al. 2021) and nutrients in a sandbanks environment. Furthermore, Emilio et al. (2021) showed that > 70% of the evaluated attributes (e.g., stomatal length, leaf area, stomatal density and thickness) in palm leaves are explained at the species-specific level. This variation in leaf attributes is relevant to the distribution of species, promoting adaptations to climate change due to the degradation in a sandbanks environment (Bedetti et al. 2011). Therefore, we reveal that the controls (e.g., environmental, and taxonomic) can influence leaf attributes differently as the evaluated biome changes. In the Cerrado, microclimate variations (e.g., environmental control, Araújo et al. 2021) influence leaf characteristics, while in the Atlantic Forest, taxonomic identity (species) is more important in controlling leaf attributes.

Conclusion

Our results demonstrate that the vegetational types of the Atlantic Forest present broad functional similarity. The plant communities of sandbanks forest, Clusia formation and beach grass and shrub formation with thickets are sensitive to high temperatures and severe droughts and thus will probably be affected as a result of extreme weather events. Tolerance to water stress is manifested in the presence of epistomatic leaves, aquiferous parenchyma, and large epidermal cells. In contrast, tolerance to heat stress is evidenced in bulliform cells, Kranz sheath, and the absence of petioles. These unique features of the beach grass community have contributed to its distinction from other vegetation types. Our results, therefore, indicate expected changes in the distribution and functioning of vegetation types in the Atlantic Forest, characterized by large patches of environmental degradation.

Author Contribution Statement

The initial design and conception of the study were carried out by Priscila Fernanda Simioni, Igor Araújo and Saulo Pireda. The identification and collection of material was carried out by Dhiego da Silva Oliveira and Marcos José Gomes Pessoa. Gabriel Amaral Ferreira and Gabriel Silva Oliveira assisted in the morphological and anatomical analyses. The first statistical analyses were carried out by Saulo Pireda and Rodrigo Barboza Braga Feitoza and the final analyses by Igor Araújo. The initial version of the article was written by Dhiego da Silva Oliveira. The final revision was made by Priscila Fernanda Simioni, Igor Araújo and Maura Da Cunha. The authors are in agreement with the article.