Allelopathic Effect of S. Macrophylla on the Growth of V. Radiata Seedlings

Allelopathic effect of S. macrophylla on the growth of V. radiata seedlings Thea Philea I. Mostralesa, Greeny Joy A. Perucho, Rhoshela Vi C. Rendon, John Gregor A. Rono, Emmerson P. Rullog, Riffcord R-Denz M. Tabula Institute of Biology, College of Science, University of the Philippines, Diliman, Quezon City (a Thea Philea I. Mostrales, e-mail: theaphilea. [email  protected] com) ABSTRACT Swietenia macrophylla, or commonly known as the mahogany tree in the Philippines, is an introduced species of the family Meliaceae that is commonly used for lumber and reforestation projects.However, based on studies, it is shown that the mahogany tree has inhibitory effects that affect adjacent growing plants. This is made possible chemically and is referred to generally as allelopathy. This study aimed to determine is S. macrophylla had any adverse effects to the growth of plants in close proximity to it. The researchers selected three mahogany trees and planted six plots of differeing distances with each plot containing ten monggo seedlings.The results obtained indicate that there is no significant difference between the growth of monggo seedlings growing near the mahogany tree to that of monggo seedling growing near the control tree based on the analysis done on the seedlings’ height, weight and survival rate. Results also indicate that distance of the seedlings from the S. macrophylla has no effect on the intensity of inhibition of the growth of the V. radiata.The results obtained can be attributed to factors that include the texture of soil, fine-textures soil having been proven to have a greater retention capacity of allelochemicals than coarse-textures soils. Also, allelopathic interactions include both promontory and inhibitory activities of phenolic allelochemicals and thus using seed germination as a bioassay parameter may be of little value. KEY WORDS: Swietenia macrophylla, allelopathy, growth of monggo seedlings, inhibitory effect of mahogany, introduced species INTRODUCTIONBACKGROUND AND SIGNIFICANCE OF THE STUDY Swietenia macrophylla, commonly known in the Philippines as mahogany, is a member of the order Sapindales, under family Meliaceae. It is a large, fast-growing, semi-evergreen tree, popular for landscaping, especially in North American and Carribean countries, where it has a vulnerable status as provided by CITES (Oldfield 1995), and for its strong wood for lumber. This tree was first introduced in the Philippines as early as 1907, and 1913 as part of the Mt. Makiling forest.It is currently used in the Philippines as a lumber tree and utilized in many reforestation projects. However, studies have shown that however beneficial S. macrophylla may be to the Philippine economy and to its environment, it also displays adverse effects to the Philippine wildlife. As a recently introduced species, the said tree has been unable to produce a natural web of life around it; there are no natural consumers of mahogany in the country, an d as such, the area around the tree will not be populated by native fauna immediately.It is also suspected that mahogany leaves contain allelopathic compounds. In a study conducted by P. Thinley in 2002, it was shown that S. macrophylla leaves inhibited the growth of Pterocarpus indicus. Allelopathic compounds inhibit growth and development of other plants when introduced to them. Allelopathy is the production of a certain plant of such compounds and should not to be confused with competition, which may or may not involve allelopathy. Allelopathy is common in the plant kingdom, spread out in random fashion across orders.Some plants are deemed invasive due to their allelopathic nature and mahogany trees are not exempt. STATEMENT OF THE PROBLEM The study aimed to determine if S. macrophylla can adversely affect the growth of plants in close proximity to it and specifically sought to answer the following questions: 1) Does mahogany affect the growth of newly planted seedlings based on the seedlings’ height and weight? 2) Is there a significant difference between the growth of seedlings within the proximity of the mahogany tree to that of seedlings within the proximity of a different tree? ) Is there a significant difference between the survival rate of the seedlings within the proximity of the mahogany to that of seedlings within the proximity of a different tree? HYPOTHESIS The mahogany tree has no effect on the growth of newly planted seedlings. SCOPE AND LIMITATIONS OF THE STUDY The study aimed to determine the effect of the mahogany tree on the growth of monggo seedlings based solely on the seedlings’ weight and height after a specified amount of time.Other possible factors that might affect the growth of the seedlings like availability of sunlight, presence of possible predators and competition with other plants in the vicinity were not included and was not accounted for in the analysis of the data obtained. MATERIALS & METHODS The researchers used monggo (Vigna radiata) as the subject plant. A frequent model plant for laboratory work in Philippine schools, V. radiata is known to be easily grown, requires little maintenance and is fast-growing, which makes it ideal for an experiment limited to a few weeks.Monggo seeds were allowed to germinate by soaking the seeds overnight. Three mahogany trees located along Beta Way in the University of the Philippines Diliman Campus were chosen based on their proximity to other trees. Since competition with other flora could affect the results, it was made sure that the mahogany trees were at least three meters away from the other trees. They were marked as T1, T2 and T3. An acacia tree, Samanea saman, with similar conditions to the experimental trees, particularly to its proximity to other trees, was chosen as the control tree and was marked as T0.To standardize the direction of planting on each tree, angles of 200 east of north and 200 west of south were used to mark radii of 3m each on the north and south side of the tree, respectively. The plots were cleaned and cleared of grass and other flora. Each radius was divided equally into three segments on each segment 10 monggo seeds were planted with a 10cm-interval per seed. Seeds planted on the north side were labelled as N1, N2 and N3 for segments positioned 1m, 2m and 3m away from the tree respectively.The labelling system was used for the south segments. The seeds were uprooted on the 9th day. Seedlings from the same segment were grouped together. The heights of the seedlings were measured using a ruler from the apex of its leaves to the tip of the roots. To standardize the measurement of the height of the seedlings, the roots were cut off at the point where the taproot has become soft and fibrous. The seedlings were then weighed using a top-loading balance. The averages of the height and weight of each segment were then determined. RESULTS AND DISCUSSIONSwietenia macrophylla is known to have inhibitory effec ts that affect adjacent growing plants. This is made possible chemically and is referred to generally as allelopathy. â€Å"The term allelopathy was coined by Molisch in 1937 to refer to biochemical interactions between all types of plants, including microorganisms traditionally placed in the plant kingdom†(Waller 1987). It is defined by Rice (1984) as any direct or indirect beneficial or harmful effect of one plant, including microorganisms, on the other through release of chemicals to the environment.Phenolics, terpenoids, alkaloids, polyacetylenes, fatty acids, steroids and many other different secondary metabolites can act as allechemicals (Rice 1984; Waller 1987; Inderjit et al. 1995). â€Å"However, the mere presence of these chemicals does not establish allelopathy, to demonstrate their involvement in allelopathy, it is important to establish 1)their direct release or indirect origin from plant-derived materials in the environment and 2) that the chemicals are present in sufficient quantities and persist for a sufficient time in soil to affect plant species or microbes† (Putnam & Tang 1986).Allelopathy is different to competition; the latter defined as the removal or reduction of factors from the environment which are vital to survivability, by some other plant or microorganism sharing the same habitat. Allelopathic chemicals, or allelochemicals, are released by higher plants through several mechanisms. These are volatilization, exudation from roots, leaching from leaves or stem by rain,dew or fog, and from decomposition of residues that contain the allelochemicals. Low molecular weight allelochemicals such as those belonging to terpenes are dispersed by volatilization.Nonvolatile allelochemicals such as alkaloids accumulate on plant surface and find their way to the soil by being leached by rainwater. Allelochemicals secreted through root exudation are of several classes. Some are alkaloids, coumarins, flavonoids, and many other types. Al lelochemicals not directly secreted by the plant, in which some pigments are an example, but reach the soil by being released through the decomposition of the plant part that contains them (Leicach et al 2009). In the S. acrophylla, allelochemicals are released by the decomposition of leaf litter. S. macrophylla leaves are a source of tannins, which is evident on the reddish brown color of the dry leaves. Tannins are phenolic compounds that also function as an allelochemical. In February, mature S. macrophyllatrees shed their leaves, which will start to decompose on the ground and consequently release tannins from the cells. Aqueous extracts from the leaves of the S. macrophylla has been shown to retard the growth of Pterocarpus indicuss eedlings (Thinley 2002). Several hydrolysable and condensed tannins were identified as growth and germination inhibitors in dry fruit, growth retarders of nitrogen-fixing bacteria in several plants, and as reducers of seedling growth in several plan ts† (Waller 1987). According to the data and the statistical analyses, the Swietenia macrophylla has no significant effect to the height, weight and survival rate of the Vigna radiate seedlings compared to height, weight and survival rate of the seedlings planted near the Samanea saman. The inhibitory effects exhibited by the S. acrophylla may have been too little or inconsistent to cause a significant change on the growth of the seedlings throughout the duration of the experiment. The compared values of the height, weight and survival rate of seedlings planted near the S. macrophyllaand S. saman are shown in table 1, table 2, and table 3 respectively. The effectiveness of allelochemicals produced by S. macrophylla may have been affected by certain factors. Tannins have been shown to be bound by the humic material I of the soil and presumably inactivated (Waller 1987).The texture of soil has been proved to affect the effectiveness of allelochemicals, favouring fine-textured th an coarse-textured soil, and evidence indicates that the greater retention capacity of fine-textured soils for at least some allelochemicals may be important in the accumulation of physiologically active concentrations of these chemicals (Waller 1987). This may have been the factor that reduced the effects of the allelochemicals involved in our experiment, owing to the beta way’s coarser soil composition. It is also proven that allelochemicals are decomposed in the soil, either abiotically or by microorganisms (Waller 1987).It is also observed that distance of the seedlings from the S. macrophylla has no effect on the intensity of inhibition of the growth of the V. radiata. The effect of distance to the height, weight and survival rate of the seedlings is seen in table 4, table 5 and table 6 respectively. This observation may have resulted from the mechanism in which the allelopathic tannins are dispersed. On the site of the study, the leaf litter covering the soil surroundin g the tree also covered to plots, which meant that the plots may have received variable amounts of allelochemicals as these leached when rains fell.The type of experimentation done was also a factor in investigating the inhibitory effects of allelochemicals. Authors argue whether seed germination is an efficient test in finding out allelopathic potential of phenolic compounds; seed germination is an important parameter for evaluating allelopathic potential of phenolic compounds (Rice, 1984; Waller, 1987), However, using seed germination as a bioassay parameter may be of little value (Stowe, 1979; Inderjit & Dakshini, 1995a). This is because allelopathic interactions include both promontory and inhibitory activities of phenolic allelochemicals.ACKNOWLEDGEMENTS The researchers would like to express their heartfelt gratitude to the following who contributed with the completion of this research: * First of all, to the Almighty God, to whom the researchers dedicate this research study. * To their families and friends who served as their inspirations and the source of very much needed support. * Ms. Lillian Jennifer Rodriguez, for her support and guidance and for lending us pink ribbons for our experiment. * Mr. James LaFrankie, for his contribution to the success of this research study. CONTRIBUTION OF INDIVIDUAL AUTHORSThea Philea Mostrales – Analysis of data, abstract of paper, SP proper Greeny Joy Perucho – Introduction and Methodology of paper, SP proper Rhoshela Vi Rendon – Analysis of data, tables, SP proper John Gregor Rono – Results and discussion of paper, SP proper Emmerson Rullog – Introduction and Methodology, SP proper Riffcord R-Denz Tabula – Results and discussion, SP proper REFERENCES Leicach, S. R. , Sampietro D. A. , Narwal, S. S. , â€Å"Allelochemicals: Role in Plant Environment Interaction†, Studium Press 2009 â€Å"Plant phenolics in allelopathy. † The Botanical Review. New York Botanical Garden. 996. HighBeam Research. 4 April 2013 The IUCN Red List of Threatened Species. International Union for Conservation of Nature and Natural Resources. 4 April 2013 Thinley P. 2002. â€Å"Negative interaction between large leaf mahogany (*Swietenia macrophylla  King) and some indigenous tree secies in lowland forest of Mt. Makiling – allelopathy, a possible cause? †Ã‚  Unpublished B. S. Forestry Thesis, UPLB-CFNR. Waller, G. R. , â€Å"Allelochemicals: Role in Agriculture and Forestry†, American Chemical Society, Washington, D.C. 1987 TABLES Table 1. Independent Samples T-test of the Height of Monggo Plants at 0. 05 significance level | Levene's Test for Equality of Variances| t-test for Equality of Means| | F| Sig. | t| df| Sig. (2-tailed)| Mean Difference| Std. Error Difference| 95% Confidence Interval of the Difference| | | | | | | | | Lower| Upper| height| Equal variances assumed| . 167| . 704| . 737| 4| . 502| 1. 000428290| 1. 357522153| -2. 768657 448| 4. 769514028| | Equal variances not assumed| | | . 737| 3. 900| . 503| 1. 000428290| 1. 357522153| -2. 807242567| 4. 808099147| Table 2.Independent Samples T-test of the Weight of Monggo Plants at 0. 05 significance level | Levene's Test for Equality of Variances| t-test for Equality of Means| | F| Sig. | t| df| Sig. (2-tailed)| Mean Difference| Std. Error Difference| 95% Confidence Interval of the Difference| | | | | | | | | Lower| Upper| weight| Equal variances assumed| . 344| . 589| -. 445| 4| . 679| -. 006665782| . 014968143| -. 048224010| . 034892446| | Equal variances not assumed| | | -. 445| 3. 819| . 680| -. 006665782| . 014968143| -. 049013784| . 035682220| Table 3. Independent Samples T-test of the Survival Rate of Monggo Plants at 0. 5 significance level | Levene's Test for Equality of Variances| t-test for Equality of Means| | F| Sig. | t| df| Sig. (2-tailed)| Mean Difference| Std. Error Difference| 95% Confidence Interval of the Difference| | | | | | | | | Lower| U pper| weight| Equal variances assumed| . 344| . 589| -. 445| 4| . 679| -. 006665782| . 014968143| -. 048224010| . 034892446| | Equal variances not assumed| | | -. 445| 3. 819| . 680| -. 006665782| . 014968143| -. 049013784| . 035682220| Table 4. ANOVA of the Height of Monggo Plants at 0. 05 significance level | Sum of Squares| df| Mean Square| F| Sig. | Between Groups| 14. 889| 2| 7. 44| 4. 598| . 062*| Within Groups| 9. 715| 6| 1. 619| | | Total| 24. 604| 8| | | | *no significant difference Table 5. ANOVA of the Weight of Monggo Plants at 0. 05 significance level | Sum of Squares| df| Mean Square| F| Sig. | Between Groups| . 003| 2| . 001| 1. 960| . 221*| Within Groups| . 005| 6| . 001| | | Total| . 008| 8| | | | *no significant difference Table 6. ANOVA of the Survival Rate of Monggo Plants at 0. 05 significance level | Sum of Squares| df| Mean Square| F| Sig. | Between Groups| . 011| 2| . 005| . 487| . 637*| Within Groups| . 065| 6| . 011| | | Total| . 076| 8| | | | *no significa nt differenceTable 7. Average Height, Weight, and Survival Rate of Monggo Plants Tree| Distance from tree (m)| Height (cm)| Weight (g)| Survival Rate| T0| 1| 16. 67| 0. 2361| 0. 9| | 2| 15. 49| 0. 2347| 0. 95| | 3| 13. 15| 0. 2074| 0. 95| T1| 1| 16. 21| 0. 2255| 1. 0| | 2| 17. 02| 0. 2567| 0. 75| | 3| 16. 73| 0. 2380| 0. 75| T2| 1| 13. 00| 0. 1688| 0. 8| | 2| 18. 99| 0. 2553| 0. 85| | 3| 16. 55| 0. 2340| 1. 0| T3| 1| 14. 22| 0. 1884| 0. 95| | 2| 16. 86| 0. 1928| 0. 9| | 3| 15. 07| 0. 2183| 0. 9| T0 = controlled tree: S. saman T1 = 1st replicate of S. macrophylla T2 =2nd replicate of S. macrophylla T3 = 3rd replicate of S. macrophylla