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The productivity and the constituents content of plants is determined by a group of factors inherent to plant and abiotics. In the first case are the biological characteristics and in the second, the soil, climate and management (Herrera et al. 2017a).These aspects has particular importance nowadays, due to the high prize of raw matters for the production of concentrate foods for animals and the fertilizers for grass cultivation (Estrada-Jiménez et al. 2019).
The use of shrubs in livestock systems had great importance during the last years, due to its nutritional, productive and environmental contribution (Schultze-Kraft et al. 2018) and among them Tithonia diversifolia (Hemsl.) A. Gray highlighted thanks to their genetic diversity (Del Valle et al. 2017), wide adaptation to different environmental conditions (Ruiz et al. 2010), high variability in the morphological indicators (Rivera et al. 2018), high biomass production (Ruiz et al. 2017) and better chemical composition (Londoño et al. 2019) than the most of grasses used in the tropic (Herrera et al. 2020).
This species, as other plants, have many organic compounds named primary metabolites, among there are in first term, the sugars or carbohydrates, which are produced as the result of the photosynthesis and are used by the plants for many functions, among them, the synthesis of secondary compounds; so these primary compounds are important in the interaction of the plant with their environment.
In accordance with Martín (2017) and Isah (2019), their presence and concentration can varied between species and varieties due to biotic factors like biochemical and physiological process of the plant (Herrera et al. 2020) and abiotics factors (geoclimatic factors, seasonal changes, ultraviolet radiation, water availability, temperature, soil composition), aspects that could cause the decrease of the photosynthetic activity of the plant and in consequent, the carbohydrates values decreased (glucose, fructose and sucrose) and are movolized for the secondary metabolites production; as well as, the nitrogenous nutrients are also used in the synthesis of more complex substances from the plant secondary metabolism like the defense mechanisms (Reyes-Silva et al. 2020).
When considered the previous exposed, the objective of this research was to evaluate the effect of the plant maturity and the climatic factors on the primary metabolites content in Tithonia diversifolia.
Materials and Methods
Reseach area, climate and soil. The study was carried out in areas of the Departamento Docente-Productivo from Universidad de Granma, in the southeastern of Cuba, Granma province, at 17.5 km from Bayamo city. Studies during two years (2014-2015) were performed and two seasons were considered, the rainy season (May-October) and dry season (November-April).
The soil in the area was calcic haptustept (Soil Survey Staff 2014), with a pH of 6.2. The content of P2O5, K2O and total N was 2.4; 33.42 and 3 mg/100g of soil, respectively and 3.6 % of organic matter.
During the rainy season, the rainfalls were of 731.4 mm; the mean, minimum and maximum temperature recorded values of 26.73; 22.31 and 33.92 ºC, respectively and the relative humidity was of 80.78; 51.02 and 96.22 %, for the mean, minimum and maximum, respectively. In the dry season, rainfalls reached values of 270 mm; the temperature was of 24.05; 18.29 and 31.58 ºC for the mean, minimum and maximum, respectively and the minimum, mean and maximum relative humidity with averages of 76.21; 44.16 and 97.03 %, respectively. Values that correspond with the historical performance for the area.
Treatment and experimental design. A random block design with for replications (plots) was used, considering as treatments the regrowth ages 60, 120 and 180 days.
Procedure. For the established species (T. diversifolia) at the beginning of each seasonal period a homogeneity cut at 15 cm soil height was performed. The samplings in each plot (0.5 ha) were carried out taking 10 random plants eliminating the first and the last plant of the plot in order to avoid the border effect. The sample was homogenized and weighed. Later, was manually separated in leaves, petioles and steams, these last with diameter inferior to two cm considering all edible biomass. Later a kilogram per each of the treatments was taken for the laboratory analysis. During the experimental stage irrigation and fertilization was not applied.
Chemical analysis. The samples were dried at room temperature in dark and ventilate room for 12 days. Later, a total of 300g were milled to a particle size of 1mm for each repetition. They were stored in amber bottles at room temperature until their analysis.
It was determined: dry matter (DM) and nitrogenous (N) in accordance with the AOAC (2016), while the contents of glucose, fructose and sucrose according the qualified method of Lane and Eynon, which is base on the reduction of Cu +2 a Cu +1 by the reducing sugars, using methyl blue as indicator (AOAC 2016).
Statistical analysis and calculations. The Kolmogorov-Smirnov tests were performed for the normal distribution of data (Massey 1951), homogeneity of variances (Bartlett 1937), as well as the analysis of variance (ANOVA) of double classification and means comparison according to Duncan (1955). To establish the functional relation between sugars and age, the regression equations (linear, quadratic, cubic, logarithmic and Gompertz) were analyzed and the descending method was used. For the choice of the better expression and their goodness of fit the Guerra et al. (2003) criteria related with the high value of the determination coefficient (R2), high significant of the expression and its parameters, low standard errors of the expression and its parameters, residue analysis and concordance test between the observed and estimated values were taken into account.
The correlation coefficients (Visauta 2007) were established between primary metabolites (nitrogen, glucose, sucrose and fructose) with the age and climatic factors. For all the above, the statistic program SPSS version 22.0 (IBM 2015) was used.
Results
The contents of nitrogen, glucose, sucrose and fructose in T. diversifica decreased with the regrowth age in 13.15, 0.008, 0.015 and 0.007 g.kg-1 in the rainy season; while, for the dry season were of 17.39, 0.002, 0.003 and 0.0009 g.kg-1, respectively (table 1).
Table 1 Effect of regrowth age on primary metabolites content
| Age, days | Nitrogen, g.kg-1 | Glucose, g.kg-1 | Sucrose, g.kg-1 | Fructose, g.Kk-1 |
|---|---|---|---|---|
| 60 | 39.52a | 0.014a | 0.028a | 0.014a |
| 120 | 31.41b | 0.005c | 0.007c | 0.003c |
| 180 | 26.37c | 0.006b | 0.013b | 0.007b |
| SE± | 1.63 | 0.001 | 0.003 | 0.002 |
| p | 0.0001 | 0.0001 | 0.0001 | 0.0001 |
| 60 | 46.42a | 0.0072a | 0.011b | 0.0037b |
| 120 | 41.87b | 0.0056b | 0.013a | 0.007a |
| 180 | 29.03c | 0.0052c | 0.008c | 0.0028c |
| SE± | 2.22 | 0.0003 | 0.0006 | 0.00054 |
| p | 0.0001 | 0.0001 | 0.001 | 0.0001 |
abc Values with common letters differ to P<0.05 (Duncan 1955)
Quadratic equations were fitted for all the indicators. All the regression coefficients were higher to 0.95 for all metabolites in both seasonal periods except for sucrose and fructose during the dry season that was 0.93 and 0.91, respectively (table 2).
Table 2 Relation of the regrowth age with the nitrogen content and Tithonia diversifolia sugars
| Indicators | a | b | c | R2 | SE± |
|---|---|---|---|---|---|
|
| |||||
| Nitrogen | 50.551 | -0.206 | 0.000399 | 0.99 | 0.3470 |
| Glucose | 00.031 | -0.000367 | 0.0000013 | 0.97 | 0.0010 |
| Sucrose | 00.072 | -0.001 | 0.0000033 | 0.96 | 0.0020 |
| Fructose | 00.039 | -0.001 | 0.0000012 | 0.95 | 0.0010 |
|
| |||||
| Nitrogen | 44.016 | 0.101 | -0.001 | 0.99 | 0.4850 |
| Glucose | 00.010 | -0.000049 | 0.00000014 | 0.99 | 0.0001 |
| Sucrose | 00.004 | 0.000155 | -0.00000074 | 0.93 | 0.0004 |
| Fructose | -00.006 | 0.000206 | -0.00000089 | 0.91 | 0.0004 |
a: quadratic term b: linear term c: independent term
R2 all to p<0.001
The correlations between sugars and nitrogen (primary compounds) with the climate factors were changeable (table 3). During the rainy season the higher coefficient (r) values were for sucrose with the rainy days and maximum temperature (-0.92 and -0.69, respectively); nitrogen with minimum, mean temperature and rainy days (-0.47, -0.46 and -0.87, respectively); glucose with minimum, mean temperature and rainy days (-0.65, -0.65 and -0.69, respectively) and fructose with the minimum relative humidity and rainy days (-0.88, -0.46 and -0.68, respectively) it is important to highlighted that the rainy days were related with all the indicators. In the dry season only the N correlated with the minimum and mean temperature, the mean, maximum, minimum relative humidity, total rainfalls and rainy days(-0.68, -0.72, -0.65, -0.65, 0.76 and -0.94, respectively) and fructose with mean, maximum temperature and total rainfalls (0.65, -0.59 and 0.58, respectively.
Table 3 Correlation between primary metabolites content and climatic factors
| Dependent variables, % | Independent variables | |||||||
|---|---|---|---|---|---|---|---|---|
| Temperature, °C | Relative humidity, % | Rainfalls, mm | ||||||
| Max. | Min. | Mean | Mean | Max. | Min. | Total | # of days | |
| Nitrogen | -0.33 | -0.47* | -0.46* | -0.31 | -0.328 | 0.20 | -0.30 | -0.87** |
| Glucose | 0.014 | -0.65* | -0.65* | 0.03 | 0.15 | -0.18 | -0.52* | -0.69* |
| Sucrose | -0.69* | -0.31 | -0.31 | -0.04 | -0.068 | -0.23 | -0.17 | -0.92** |
| Fructose | -0.24 | -0.44 | -0.44 | -0.21 | -0.238 | -0.88** | -0.46* | -0.68* |
| Nitrogen | 0.33 | -0.68* | -0.72** | -0.65** | -0.65* | -0.65* | 0.76** | -0.94** |
| Glucose | -0.13 | -0.001 | 0.14 | -0.01 | -0.008 | -0.007 | -0.14 | 0.099 |
| Sucrose | 0.32 | 0.03 | -0.33 | 0.04 | 0.04 | 0.042 | 0.32 | -0.22 |
| Fructose | 0.66* | 0.21 | -0.59* | 0.24 | 0.24 | 0.24 | 0.58* | -0.29 |
Max: maximum Min: minimum
*P<0.01 ** P<0.001 *** P<0.0001
Discussion
The reduction of primary metabolites (table 1) has been described by Salas et al. (2015), Méndez et al. (2018) and Paumier et al. (2018), whose found in Phaseolus vulgaris, Moringa oleifera y Gliricidia sepium that values of carbohydrates and nitrogenous compounds were closely related with the succession of phenological events, from the early growth up to the flowers formation and flowering. From the last one, the general decrease of sugars and protein compounds begin, since the performance of energy metabolites in accordance to the morpho- structural variations depends on the species, nutritional state and edaphoclimatic conditions in which it is cultivate.
The obtained models and the higher values of R2 reported in table 2 are similar to those informed by Herrera et al. (2017a b), Paumier et al. (2018) and Verdecia et al. (2018), when evaluating the age effect and climatic factors in the nitrogen content in forage species in Valle del Cauto. They associate the N decrease with the cut frequency due to the reduction of the protein compounds synthesis, the decrease of the amount of leaves, increase of the fraction stems and increase of the structural carbohydrates synthesis (cellulose and hemicellulose) and phenolic compounds (lignin).
Other authors as Torres-Navarrete et al. (2019), associate this performance with the high proportion of stems in the sample, since, usually, in the literature are reported N values of approximately 33.6 g/kg DM in leaves, while in the stems range between 11.2 and 22 g/kg DM. Generally, the observed values in the analyzed plants are similar to those of the temperate legumes. The founded contents are in the range established by Camacho-Escobar et al. (2020) for tropical legumes, given importance to the results of this study.
On the other hand, Rivera et al. (2018) stated that T. diversifolia is a plant which is characterized of having excellent quality, due to its low fiber content and good relation of nutrients in their foliage, mainly high content of nitrogenous compounds in its first vegetative phase. Herrera et al. (2020) and Paumier et al. (2020), founded nitrogen concentrations of 26-46 g/kg of DM, while Verdecia et al. (2021) notified similarities regarding the content and nitrogen variability of T. diversifolia and G. sepium, emphasizing the importance of using the combination of legume forage species in animal feeding.
The trees quality varied in the different biomass components. Leaves has high nutrients concentrations than the branches and stems, and this variation has also related with the age, having the young leaves more nitrogen content than older leaves (Lodoño et al. 2018). These results coincide with those reported for this species (Gallego-Castro et al. 2017, Cerdas-Ramírez 2018 and Rodríguez et al. 2019).
The variability in the sugars with the age is due to the differentiated photosynthetic capacity of each species, related with the content of minerals and potassium, which is the mediator of metabolism and of the primary carbohydrates transport in the plant (Martín 2017).
The content of soluble carbohydrates is link to the morpho-structural development of plants. The concentrated reserves of these compounds, in fewer amounts, in the growing points (buds) favor the leaves concentrations of saccharides after the regrowth emission. However, although in general way these aspects are described, from the physiological point of view, the performance of energetic metabolites in function of morphologic variations depends on the species, nutritional state and edaphoclimatic conditions in which it is cultivated (Cao et al. 2011).
Li et al. (2018) when refering to the carbohydrates movement stated, that reserve content reach it higher value in the old leaves at the beginning of the flowering and were moving during the fruit development but, observed the faster decrease of reserves in roots and leaves during the flowering, with a transitional increase of them at the beginning of the abscission of fruits and marked decrease up to a lower value at the end of the physiological abscission period, with which the fruit nutrition depends on the photosynthesis than of the tree reserves. Aspects that can explain what occur in this research.
The fluctuations of the non structural carbohydrates of E. variegata at the ages of 60 and 120 days found by Verdecia et al. (2020a) were attributed to genetic factors, edaphoclimatic conditions and the used cultivation techniques. The plant maturity, the transport and storing conditions, are important when evaluating the carbohydrates content, if it taking into account that the fructose is synthesized during the first growing stages. The sugars concentrations in Tithonia were similar to those obtained in the foliage of other non- legumes plants like Morus alba, Trichantera gigantea, Cnidoscolum aconitifolium and Ficus carica (García et al. 2008). However, the amounts were lower to that informed in some legumes of traditional use as forage (Yang et al. 2018), in which the value of these compounds in mature foliage has been determined. These confirm the above described, where the intervention of different factors in the content of those sugars is explained.
On this matter, it is known that generally the non- legumes compared with legumes has higher amount of soluble carbohydrates when both groups are in the same phenological state (Flores-Villa et al. 2020). However, it has been showed in different experimental conditions, that the biomass age influence on the concentration of carbon hydrates (Guerreiro et al. 2018).
Salvucci et al. (2010) when studied the content of glucose, fructose and sucrose in Parthenium argentatum foliage found the higher concentrations during the rainy season, due to the higher photosynthetic activity and consequently increase of carbohydrates formation. Brueckner et al. (2010) found 0.09 - 0.11; 0.15 - 0.16 and 0.03 - 0.04 g/kg DM of glucose, fructose and sucrose, respectively, values higher than those reported in this study. This could be attributed to the differences in the experimental conditions and of species.
Regarding the correlation between nitrogen, glucose, sucrose and fructose with the age and climatic factors (table 3), the results coincide with those found by Herrera et al. (2017 a b), Paumier et al. (2018) and Herrera et al. (2020) who founded higher correlation coefficients (r) between regrowth age, total rainfalls and rainy days with the nitrogen and sugars.
In this sense, Hernández-Espinoza et al. (2020) explained that the stress produced by abiotics factors affects the kinetic of carbohydrates metabolism, in a way that the balance of environmental factors influence on the source-utilization relation and, therefore the final accumulation of this compounds in the storage organs. Hence, that in the improvement process of the different species and genotypes selection had been taking into account that these can endure the exigencies caused by the adverse abiotics conditions , for that, the fit capacity or tolerance of plants to this conditions don’t be limited.
Herrera et al. (2017a) when correlate the chemical composition and climatic variables in this species established some hypothesis: a) all seems to be that the changes in the chemical composition are less sensitive to temperature variations; b) it is more important the rainfalls distribution than the total of them in the variability of chemical composition. In addition if these results are compared with those obtained in meadow grasses, as well as those reached in Leucaena are totally different. (Herrera et al. 2017 b), so it could be established the third hypothesis that are variations in the intensity and elements which intervene in the synthesis of the mentioned compounds. As hypothesis those needs specific researchers which explain this performance.
Conclusions
The regrowth age had marked effect on the primary metabolites content (nitrogen, glucose, fructose and sucrose) which explain the close relation, thorough the established regression equations. Regarding climatic factors the correlations were changeable as being marked during the rainy season, while in the dry season only nitrogen and fructose were related. This maintains that the higher variability and mobility of the main primary metabolites is due to the plant physiological processes.
