Brazilian pepper (Schinus terebinthifolius) seedlings development under different luminous intensity

Brazilian pepper is a native mastic that despite its high potential is still underutilized nationally. Its main uses guiding use of herbal extracts for cosmetic purposes and as a suitable plant for reforestration of degraded areas. This research aimed to evaluate the influence of luminous intensity (shading) in the early development of Schinus terebinthifolius seedlings. For that purpose, 64 seedlings were subjected to restriction in four light conditions: 0, 35, 50 and 80%. The following parameters were measured: Number of leaves (NF), plantule size (TP), stem diameter (DC), root volume (VR), leaf dry matter (MSF), stem dry matter (MSC), shoot dry matter (MSA), root dry matter (MSR) and total dry matter (MST). The results show that the species S. terebinthifolius is sensitive to bright gradient imposed on the plants. According to the equation, the point corresponding to maximum development of roots is near to 50% light restriction.


INTRODUCTION
Brazilian forested areas have been suffering significant levels of deforestation due to the advancement of agricultural frontiers, logging activities, construction of hydroelectric power plants and real estate speculation.In this scenario, initiatives for the implementation of conservation projects and restoration of these areas are growing, particularly with the use of native tree species.Due to the lack of knowledge on the production protocols of seedling production, their ecological and silvicultural behavior under different environmental conditions, studies for the development of forestry and conservation programs are extremely important (Pacheco et al., 2013).
Due to the growing awareness about the importance of environmental preservation and the advancement of the laws that regulate human actions on the protection of forests, in recent years there was increased an incentive for the planting of native species for reforestation (Nascimento et al., 2012).The tree is known as Brazilian red-pepper, and by various other names, Schinus terebinthifolius Raddi is an Anacardiaceae, pioneer, native from Brazil (Fernandes et al., 2008).
This variation in names is given mainly by its fruits having the appearance of a red to rose small pepper, with fruits are also called by rose pepper, pink pepper, poivre rose among other names (Lenzi and Orth, 2004).
The species has numerous medicinal and phytochemical potentialities, leaves and bark extracts have been used as potential antimicrobials.Its fruits (pink pepper) have also been standing out in national and international markets, usually used as a food flavoring (Lenzi and Orth, 2004).
Currently, S. terebinthifolius has been widely used in the revegetation of riparian forests and areas destroyed and contaminated by open pit mining.The ease of cultivation in nurseries, the high percentage of germination and great hardiness are the main reasons to use this tree in environmental reforestation (Almeida and Leite, 2010) and even in urban areas.
The native species S. terebinthifolius Raddi (Brazilian pepper) is used in protective reforestation, as a cover for late secondary and climax species and it is indicated for the restoration of degraded areas, as they have small fruit highly sought after by birds.It also has other uses, such as dyeing and strengthening of fishing nets, because its bark contains a high quality pigment; animal feed (leaves); human food (fruits are used as black pepper substitutes) and medical uses (Andrade and Boaretto, 2012).
The use of native tree species in reforestation programs is very promising because they are better adapted to local edaphoclimatic conditions and, therefore, they facilitate the establishment of vegetation and its relations with the regional fauna (Almeida and Leite, 2010).
However, it is known that light intensity to which a plant is subjected affects their vegetative growth by exerting a direct effect on photosynthesis, stomatal conductance and chlorophyll synthesis, and other physiological processes (Marenco and Lopes 2009), which is a determining factor on the initial development of woody species.
Considering that researches with Brazilian pepper are relatively new and therefore few practical results were actually achieved (Fernandes et al., 2008).Thus, the present study aimed to evaluate the initial development of S. terebinthifolius seedlings submitted to different light intensity for a better development.

MATERIALS AND METHODS
The experiment was conducted in an experimental delimitation in completely randomized blocks (DIC) design, with four levels of shading (treatments) (0, 35, 50 and 80%) and 12 repetitions (seedlings).The Brazilian pepper seedlings were transplanted 40 days after seed germination for 1.5 L plastic bags and stayed for another 60 days in their respective environments (0, 35, 50 and 80% light restriction).We used a commercial substrate composed of pine bark, sand, vermiculite and vermicomposting, with the following characteristics: Electrical conductivity 1.5 ± 0.3 (dS m -1 ), density 480 kg m -3 , pH 6 ± 0.5, maximum humidity 60% matter matter -1 , water retention capacity 60%.
The seedlings were maintained with adequate supply of water throughout the experimental period, with daily watering.There was no need of any disease or pest control on the plants during the evaluation period.
During the experiment this period, we performed four biweekly evaluations every 15 days plants development curve based on these biometric parameters over time.
Destructive and non-destructive analysis on four randomly chosen seedlings per treatment every fifteen days included: Number of leaves (NL), seedling height (SH), stem diameter (SD), root volume (RV), leaf dry matter (LDM), stem dry matter (SDM), shoot dry matter (SDM), root dry matter (RDM) and total dry matter (TDM).
The root volume was determined in a test tube, emerging all the fresh root matter in known volume of water in the tube, the displaced volume of fluid after the emergence of the root corresponds to the root volume in cm³.Plant height was determined with the use of a ruler and the stem diameter by a caliper.Data was tabulated and submitted to analysis of variance and regression analysis using the statistical program Sisvar (Ferreira, 2003), and the graphics were generated from the equations obtained from Origin 8.0 software.

RESULTS AND DISCUSSION
According to the summary of the analysis of variance (Table 1) it was noticed significant difference only for the volume and root dry matter parameter as function of time.These results show us that the seedlings root development had a significant initial development during the first 60 DAT.
No significant differences were detected from the analysis of the other quantified variables.During the experimental period plant hardiness was improved (Grossnickle, 2012) and little or no interference was detected in aboveground growth.
Although expected, variations in light environment did not promote increase in the shoots of the Brazilian pepper seedlings; however, it was observed that in this species such variations significantly influenced root development.It must be emphasized that these seedlings, after field planting being transplanted in the field, will possibly show differences in other parameters (Fisichelli et al., 2014).It was observed a rapid root growth of Brazilian pepper seedlings during the first 60 DAT (Figure 1), where in both cases, the plants submitted to 50% shading showed the best values, suggesting that this shading level provided better root development conditions.These results showed plant's survival strategy during its initial development (Pinheiro et al., 2005) (Figure 1).Table 2 shows regression equations for Brazilian pepper root development according to shading levels.
According to Reis et al. (2006), root growth is a essential function when planting in the field, favoring seedling survival especially under water stress conditions.
For Fisichelli et al. (2014) root related properties are the most important for seedling adaptability in adverse environmental condition.Shading presents itself as excellent management for root development of Brazilian pepper seedlings, a result so far not reported in any bibliography.
Regarding to the variance analysis for the shading percentage, it was found significant difference at 1% significance (P<0.01) for root volume parameters (RV) and leaf dry matter (LFM); and at 5% significance (P<0.05) for the total dry matter parameters (TDM).For the other parameters, the different shading levels did not  3.The lack of influence of shading levels on Brazilian pepper seedlings for leaf number (NL), plantule size (PS), stem diameter (SD), stem dry matter (SDM), shoot dry matter (SDM), root dry matter (RDM) can be explained by the rapid adaptation of the environmental conditions in which the seedlings were exposed (Campos and Uchida, 2002).Scalon and Alvarenga (1993) commented that seedlings of tree species have very different behavior regarding their response to light quantity supplied, particularly for the vegetative growth of shoots and roots.
The little influence of shading levels in seedlings development can be attributed to phenotypic plasticity that these species have to germinate and develop into different environments (Mota et al., 2013).
Regarding the root volume values in Figure 2(a), we observed lower values under treatment in full sun (0% light restriction), showing that the practice of shading helps in seedlings root development, and there is a clear trend towards greater root development of S. terebinthifolius seedlings in environments with higher light restriction.Campos and Uchida (2002) when working with tree seedlings in the Amazon, also noted the increase in root development caused by shading, which reflect a balance in biomass (b) production to the roots.This increase in root volume can be explained as a mechanism that plants submitted to shading present greater matter accumulation, requiring greater absorption of water and nutrients, a strategy that will ensure the plant withstand Table 3. Sums of squares for the number of leafs (NL), seedling height (SH), stem diameter (SD), root volume (RV), leaf dry matter (LDM), stem dry matter (SDM), shoot dry matter (SDM), root dry matter (RDM) and total dry matter (TDM) parameters.the physiological condition in shaded environments (Dutra et al., 2012b).Thus, seedlings with greater development in the root system, can present better condition adapting to harsh environments, such as low water availability, and this characteristic, therefore, of utmost importance for the survival of seedlings (Figueirôa et al., 2004;Taiz and Zeiger, 2004;Mota et al., 2012).As for the average values for leaf dry matter (Figure 2b), the data showed that the higher the light restriction the greater the leaf matter accumulation.This result is explained by the need for light absorption for the photosynthetic process, and with low light the leaf expansion is stimulated, resulting in higher leaf dry matter values as a compensatory mechanism to low sun exposure (Campos and Uchida, 2002;Chaves and Paiva, 2004).It should be noted that not always higher light conditions reflects in increased photosynthesis and plant development since the development of C3 plants can also be limited by photorespiration.Dutra et al. (2012b), also observed an increase in copaiba seedlings biomass according to shading in which they were subjected, according to Lima et al. (2008), the photosynthetic process occurs mainly in the leaves, therefore, plants that have greater leaf biomass have also greater availability of photoassimilates.Regarding the total dry biomass values (TDM) (Figure 3), Brazilian pepper seedlings showed a quadratic behavior, with biomass accumulation until 57% shading level, and from this point there is biomass accumulation reduction, this decrease in higher levels of shading is due to the low adaptability of Brazilian pepper seedlings in highly shaded environments.

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Similar results were obtained by Scalon et al. (2008) in croton (Croton urucurana Baill) under 50% shading and Mota et al. (2012) in angico (Anadenanthera falcata Benth.Speg) with shading values ranging between 50 and 70%.Rego and Possamai (2006) and Dutra et al. (2012a) concluded that the development of seedlings in average shade conditions is, for most tree species, the solution to growth stimuli and largest biomass accumulation by the plant.
According to the equation shown (Figure 3), the point corresponding to the maximum total dry biomass is 53% light restriction, which should be adopted in Brazilian pepper seedling production systems, once higher biomass values reflected in seedling harnening and greater seedlings ability to survive (Ramos, 2004).

Conclusion
According to the results obtained in this study, we observed a quantitative influence of shading in the initial development of S. terebinthifolius native species.Brazilian pepper seedlings presented initial root development within the first 60 DAT, and the light restriction of 50% was the most indicated for growth parameters.Among the evaluated parameters, shading levels influenced root volume, leaf dry matter and total dry matter, and the maximum plant development was reached with approximately 53% light restriction.

Figure 1 .
Figure 1.Roots volume (a) and root dry biomass (b) of Brazilian pepper seedlings (S. terebinthifolius) under different levels of shading as a function of days after transplanting.

Figure 2 .
Figure 2. Brazilian pepper seedlings root volume (a) and leaf dry matter subjected to different light restriction levels.

Figure 3 .
Figure 3. Brazilian pepper seedlings total dry biomass under different levels of shading.

Table 1 .
Summary of analysis of variance for the development of Brazilian pepper seedlings (S. terebinthifolius) versus time.