Balance of elements and tolerance of the Terminalia catappa L . to seawater salinity

1 Center of Science and Technology Agrofood (CCTA), Federal University of Campina Grande (UFCG), Pombal, PB, Brazil. 2 Nucleus of Graduation in Education in Agrarian and Ground Sciences, Federal University of Sergipe, Campus do Sertão, Nossa Senhora da Glória, SE, Brazil. 3 Academic Unit of Agricultural Engineering, UFCG, Rua Aprígio Veloso, 882, Campina Grande, PB, Brazil. 4 Center for Social, Human and Agrarian Sciences, Federal University of Paraíba, Bananeiras, PB, Brazil.

As it is very resistant to salinity and wind effects, Indian almond trees have been used for landscaping, especially in beaches, town squares and other urban areas of tropical and warm-humid climates.Many authors have also inventoried this type of tree (Silva et al., 2010;Cariolano et al., 2014).With a medium to large size, the Indian almond tree is 15 to 40 m high and has a wide and scattered treetop over horizontal branches, which originate from the straight to tortuous trunk in an evenly spaced manner.The trunk is composed of a brownish, rough and fissured bark with a diameter varying from 55 to 155 cm (Ivani et al., 2008).
Its varnished and oval-shaped leaves present leather texture and are large, with a size of 16 to 36 cm long by 9 to 25 cm wide.The colors of bottom and upper faces of the leaves are light and dark green, respectively, which change to yellow and red at a certain time of the year.Indian almond trees present small flowers, which are greenish-white and grouped into elongated ears; and fleshy fruits of about 5 to 6 cm long by 3 to 4 cm wide, with a fibrous pulp and a single seed.The conical seed is hard, light, flat and elongated, with about 2.3 long by 0.6 cm wide (Gomes, 2007).
The Indian almond tree is suitable for the harsh coastal conditions as its top is full and bushy, providing shade during drought spells in the tropics.This condition highlights the potential of such species for afforestation in urban areas.It is important, however, to take care when pruning the Indian almond trees, since the mismanagement may disfigure the treetop (Patro, 2013).Moreover, because of its rapid growth characteristics and wide treetop, it is a plant with a great potential for carbon sequestration and is used as medicinal plants.For example, Anuracpreeda et al. (2016) highlight that the ethanol extract of T. catappa L. from leaves possesses the anthelmintic activity against Fischoederius cobboldi, and this extract has a potential to be an efficacious anthelmintic drug for treatment of paramphistomosis.
Considering that Indian almonds are ornamental trees, it is common to notice their planting in coastal areas, often without the use of irrigation and subject to adverse conditions of soil and climate (e.g., sea breeze).Under such conditions, the concentration of salts in soil and water tends to be high and the plants must be able to survive, once the inflow of soil salts ions to the plant tends to cause osmotic or ionic disorders (Brito et al., 2014;Syvertsen and Garcia-Sanchez, 2014).As a result, Indian almond trees may be used for the recovery of degraded areas by salts in order to sequester atmospheric carbon.
Nevertheless, studies must be carried out in order to identify the mechanisms of salinity tolerance in Indian almond trees, which may be assessed by the balance of salts in parts of the plant, such as leaves, almond barks and almonds.Thus, the objective was to evaluate the content of micronutrients and macronutrients in leaves, almond barks and almonds collected in trees under different conditions of salinity in Brazil.

MATERIALS AND METHODS
The research consisted of an exploratory survey on Indian almond trees in eight sites located in Brazil's Northeast Coast, which were chosen based on their exposure to four different seawater salinity conditions, namely: (1) Trees located around 120 km from sea breeze; (2) Trees under sea breeze; (3) Trees in seashore without direct exposure of roots to seawater; and (4) Trees in seashore with direct exposure of roots to seawater.
In Table 1, the geographic coordinates of each site chosen for this study is shown.Each investigated plant provided samples of leaves and fruits.The leaves were collected from the middle third of the plants, considering their degree of maturity and exposure to solar radiation.The leaf samples were composed of 10 leaves for each repetition, which were stored in paper bags and sent for analyses at the Irrigation and Salinity Laboratory of the Federal University of Campina Grande, Brazil.Only the ripe fruits samples with light color and soft pulp were considered for this research.Before analysis and chemical characterization, 20 fruits for each repetition were defragmented in pericarp and almond.Taking into consideration the factors, the research is composed of Indian almond trees from eight sites, with analyses from three organs in four repetitions, which amounts to 96 parcels.All collected material was sent to the Irrigation and Salinity Laboratory of the Federal University of Campina Grande, Brazil.The samples of leaves and fruits were washed with running and deionized water in order to remove impurities from their surface.Hereafter, they were placed in a forced air circulation oven at 65°C and dried to constant weight.Finally, the fruits were partitioned into pericarp and almonds.The dry samples were weighted in an analytical balance in order to obtain the dry mass of leaves, pericarps and almonds.After weighing, all parts were grinded in a Wiley mill, using a vertical rotor with fixed hammers, and passed through a stainless steel wire mesh (1.7 mm).Later, we determined the levels of macronutrients (N, P, K, Ca, Mg and S) and micronutrients (Cl, Cu, Fe, Mn and Zn) in plant tissues.By using dried masses and nutrient contents values, it was possible to determine total contents of macro-and micronutrients in both the leaves and parts of the fruit.For this, we did not consider the effect of dilution.
We used analytical techniques to determine the contents of nutrients in the trees via nitric-perchloric acid and sulfuric acid wet digestions.The chemical analyses for P, K, C, Mg, Zn, Cu, Mn, Fe, Na and Al were conducted in accordance with the methods recommended by EMBRAPA (2009) and UFV (1997).For the nitricperchloric acid digestion, we used 500 mg of dried and grinded material in the digestion pipe; added 6 ml of a mixture of HNO3 (65%) and HClO4 (70%) in the ratio of 2:1 (v/v); and considered the volume of 25 ml for analysis by atomic absorption spectrometry.As for the sulfuric acid digestion, we passed 100 mg of grinded dry matter through the digestion pipe; added 1 mL of H2SO4 and carried out a pre-solubilization (± 12 h) into the biodigester block at 300°C for 35 min; cooled completely and added 1 ml of H2O2 p.a. 30 vol. for 15 min at 200°C; and considered a volume of 25 ml for analysis by spectrophotometer at 480 nm.
The data were submitted to analysis of variance and, whenever significant (>5%), subject to: (1) Tukey's range test, when comparing the parts of the plant; and (2) Scott-Knott clustering test, when comparing the sampling sites.In order to do this, we used the SISVAR software (Ferreira, 2014).

RESULTS AND DISCUSSION
According to a summary of the variance analysis in Table 2, there was a significant effect (p < 0.01) in the interaction among locations and plant parts for the formation of dry matter as well as in the contents of macro-and micro-nutrients presents in the Indian almond trees.Likewise, there was isolated effect of the factors.These results are similar to those found by Ferreira et al. (2005).The later authors, studying the levels of macroand micronutrients in maize plants subject to salt stress, verified the effect of salinity over cationic contents and their relationships.The Indian almond trees used in this study were chosen from different exposures to seawater salinity and other climatic factors, such as wind and temperature.These conditions have become essential as a comparative source of analysis, since there were effects in the interaction between factors.
Differences were observed in the production of dry matter, conformed to the collection site and type of exposure the trees were submitted (Table 2).In this regard and in accordance with the Scott-Knott test (5% level), it was noted a distinction between two groups in the mass production of leaves.We observed higher averages in species harvested in the regions of Jacarapé beach and Maragogi (Table 3), which were exposed to seashore/seawater and sea breeze, respectively.
For the pericarp mass formation, there was also a distinction between two groups.The highest averages were observed in the fruits collected from Jacarapé beach, Maragogi and Campina Grande.It is important to notice that in Campina Grande, taken as an "untreated control" site, there was not any effect arising from seawater salinity.In view of that, even under seawater or sea breeze exposure, the Indian almond trees maintained their genetic potential.On the other hand, the smaller values observed in different sites may be related to other limiting factors, such as nutrient availability (trees were collected in areas with weathered soils and low fertility, which could be confirmed when studying the contents of nutrients in plant parts).
For the almond mass production, there was no significant difference of means when considering the collection sites or the exposure to seawater salinity.As a result, the Indian almond trees prioritize the formation of almond mass whether they are subject or not to salinity conditions.This outcome can be related to an embryo protection mechanism, which was also observed by Nepomuceno et al. (2001).Such authors, studying physiological mechanisms of drought tolerance in plants, noticed enzymatic complexes that can lead to induction and enable changes in the expression of various genes, inducing protection of the plants against stress, as may have occurred in Indian almond trees when exposed to seawater salinity.
Based on the results of macronutrient contents found for leaves, pericarps and almonds (Tables 4 and 5), it was verified that the greater difference among collection sites occurred in leaves.According to Scott-Knott and Tukey tests (5% level), there was no difference between collection sites when analyzing the contents of macronutrients in almonds, with exception for phosphorus content.This result indicates the ability of the trees to protect embryos from toxic compounds and maintain a concentration of elements enough to meet the needs of a new individual.
The primary macronutrient contents (N, P and K) found in the leaves of the Indian almond trees presented the greatest difference among treatments.According to the Scott-Knott test (p < 0.05), there were three groups that stood out, being the highest contents of macronutrients observed in trees collected in Jacarapé beach, under sea breeze conditions.In opposition, the leaf samples collected in Campina Grande provided the lowest contents of primary macronutrients.Even though, there were no visual signs of deficiency in their leaves.From this, it is possible to denote that the Indian almond trees are able to maintain the balance of essential macronutrients in their leaves.These results differ from those obtained by Carmo et al. (2011), who found that salts affect the availability of water and cause nutritional disorders in trees, depending on the type of salt and plant genotype.
In relation to secondary macronutrients (Ca, Mg and S), the results presented differences among the elements.As for the calcium content, we noted that the highest contents were detected in samples collected in Campina Grande, where there is no exposure to any kind of seawater salinity.The contents reduced between 37 and 79% when compared to those from samples collected in sites exposed to seawater salinity.This may result from an ionic competition between sodium and calcium, which can interfere in cell wall formation and reduce membrane integrity (Taiz et al., 2017).
As for the magnesium and sulfur, the greater contents were observed in samples of leaves collected from Indian almond trees in Jacarapé, which were under the sea breeze.These outcomes reinforce the good nutritional conditions of such trees, even when subject to tress conditions.The magnesium and sulfur elements are essential in the formation of chlorophyll molecules and proteins, respectively (Taiz et al., 2017).
By studying the chlorine and sodium contents in leaves, pericarps and almonds of the Indian almond trees collected from the different sites, it was noticed a significant interaction among the factors (Table 6).It was also identified that there were differences in the results among sites and among tree parts, in isolation.This result can be attributed to the different exposures to seawater salinity and the tree need for protection minimized by these circumstances.
The highest contents of chloride and sodium were observed in the pericarps, for which there was also the greatest difference among sampling sites (Table 7).It is important to point out that the non-occurrence of significant differences in chlorine and sodium contents for almonds reveals the potential of Indian almond trees to hold the protection of their embryos.Such behavior avoids toxic levels of some elements, especially sodium, even when exposed to seawater salinity conditions.As a result, these trees have a great potential in afforestation of areas with salt problems and can assist in carbon sequestration processes.When analyzing the chlorine contents in leaves (Table 7), it was verified that the highest values were observed in the samples collected from trees located in Maragogi, under sea breeze; in Aracaju, under seashore conditions; and Tambaú beach, exposed to seawater.However, in general, the levels of this element in trees exposed to some salinity condition were higher than those obtained from samples of Campina Grande, which were not exposed to seawater salinity whatsoever.Chlorine accumulation may be interesting, since it is an essential micronutrient and has great importance in the growth and development of trees, performing various functions (Carvalho et al., 2009).
In the leaf samples collected in Maragogi and Tambaú, which were in seashore with direct exposure of roots to seawater, it was noticed that the chloride contents were low and even similar to those observed in the samples from Campina Grande.This result may be due to the water flow and diversity of ions present in seawater.By making a remark to the values obtained for the pericarps, it may also be caused by the acting of the leaves as protective bodies, which accumulates ions that are toxic to the tree.
With regard to the sodium contents in the pericarps (Table 7), the highest values were noted in trees under exposure of roots to seawater in Maragogi and Tambaú beach.High values were also found in the samples from Aracaju and Tambaú beach, both located in seashore without direct exposure of roots to seawater.Although these values have been high, the Indian almond trees have not accumulated sodium in almonds and kept the highest contents in the pericarps, confirming that this is an organ of accumulation and protection against stresses.
In general, sodium accumulation in leaves and pericarps of the Indian almond trees exposed to seashore and seawater did not compromise the macronutrient contents.In fact, all values of macronutrients were higher than those observed in the samples collected in Campina Grande, which was considered to be a control site.The results reinforce the importance of Indian almond trees as species that can be used in afforestation of areas with salinity problems.They might also contribute to carbon sequestration, although they may grow and develop deficiently under such conditions, as pointed out by some authors (Gheyi et al., 2016;Neto and Tabosa, 2000).

Conclusion
The exposure to the seawater salinity did not change the macronutrient contents in the almonds, what is a protective mechanism of the Indian almond tree.Indian almond trees can be used to reforest areas with salinization problems.In order to protect itself from seawater salinity, the Indian almond tree compartmentalizes sodium salts in the pericarp of the fruit.Indian almond trees can be used in a lot of ways, being an important crop for use in saline areas or under salt stress; however, it is necessary to study genotypes for selection of materials tolerant and productive.

Table 1 .
Collection sites, exposure conditions and geographic coordinates of the Indian almond trees used for this research.Thomson and Evans, 2006), such as in Brazil, being very common to see this plants on seashores due to its rapid growth and shadows it produces.In Brazil, species of Indian almond trees are geographically distributed in Northeast (States of Bahia, Paraíba, Pernambuco, Sergipe, Ceará, Piauí and Alagoas), North (States of Acre, Amazonas and Pará), Midwest (State of Mato Grosso do Sul), Southeast (States of Minas Gerais and São Paulo) and South (State of Paraná).

Table 2 .
Summary of the variance analysis for dry matter and contents of macronutrients in parts of Indian almond trees from different sites in Brazil Northeast Coast and considering the exposure to salinity seawater.

Table 3 .
Mean comparison test (Tukey)for dried masses of leaves, pericarps and almonds; and mean clusters (Scott-Knott) among sites of collection of the Indian almond trees under different types of exposure to salinity.Means followed by the same small letter among collection sites and same capital letter among plant parts do not differ according to Scott-Knott and Tukey tests (p < 0.05), respectively. aC

Table 4 .
Contents of nitrogen, phosphorus and potassium in leaves, pericarps and almonds of Indian almond trees collected from different sites and under different types of exposure to salinity.
aC Means followed by the same small letter among collection sites and same capital letter among plant parts do not differ according to Scott-Knott and Tukey tests (p < 0.05), respectively.

Table 5 .
calcium, magnesium and sulfur contents in leaves, pericarps and almonds of Indian almond trees collected from different sites and under different types of exposure to salinity.
aCMeans followed by the same small letter among collection sites and same capital letter among plant parts do not differ according to Scott-Knott and Tukey tests (p < 0.05), respectively.

Table 6 .
Summary of the variance analysis for micronutrient contents in parts of Indian almond trees from different sites in Brazil Northeast Coast and considering the exposure to salinity.

Table 7 .
Contents of chloride and sodium in leaves, pericarps and almonds of Indian almond trees collected from different sites and under different types of exposure to salinity.the same small letter among collection sites and same capital letter among plant parts do not differ according to Scott-Knott and Tukey tests (p < 0.05), respectively.
aC Means followed by