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La presencia de muclago en las races areas en Monteverde, Costa Rica
Presence of mucilage on aerial roots in Monteverde, Costa Rica
Many hemiepiphytes produce aerial roots and some have mucilage on the growing tips of these roots. The purpose of this study was to determine if mucilage varies at different altitudes in the Monteverde Cloud Forest in Costa Rica. Mucilage may serve to protect the roots from the dry environments, or from altitudes more prone to fungal infections since it has both high water storing capacities and anti-fungal properties. Transects were run along different altitudes, and samples of plants mucilage were taken, measuring the weight and length of the mucilage. Monstera was the most common plant with mucilage found in the study and was found at all altitudes ranging from 1,400 m to 1,800 m. There were a total of 12 Monstera plants, two Pitcairnia plants, and one Philodendron plant with a total of 34 mucilaginous roots. Twenty-three of the mucilaginous aerial roots were found on the genus Monstera (Araceae), 4 on Pitcairnia brittoniana (Bromeliaceae) and 7 on Philodendron (Araceae). No correlation was found between the weight and length of mucilage, compared to altitude of all three genera (Spearman rank correlation, N = 32; R2 = 0.135; p = 0.44 and N = 32; R2 = 0,86; p = .62, respectively). No correlation was also found for Monstera roots only, for weight and length compared to altitude (Spearman rank correlation, N = 23; R2 = 0.10; p = .12 and N = 23; R2 = .004; p = .759, respectively). A trend could be seen in the total mucilage frequency for low and high altitudes for Monstera. In this case, 16 Monstera were found at low altitudes, and seven at high altitudes, but this difference was not statistically significant (chi-squared test, x2 = 3.52, df = 1, p = 0.06). In conclusion, no altitudinal difference was found in mucilage size, suggesting genetic determinants might be playing a role, but twice as many Monstera were found at low altitudes compared to high altitudes, although further studies need to be done to clarify the trend.
Algunas plantas hemiepfitas producen races areas y algunas de estas presentan mucilago en las puntas de estas races. El propsito de este estudio fue determinar si el mucilago vara en las diferentes altitudes en el bosque nuboso de Monteverde en Costa Rica.
Text in English.
Cloud forest ecology--Costa Rica
Ecologa del Bosque Nuboso--Costa Rica
Tropical Ecology 2008
Hemiepiphytes, Root development--Monteverde Cloud Forest Reserve
Ecologa Tropical 2008
Hemiepfitas, desarrollo de races--Reserva Bosque Nuboso de Monteverde
t Monteverde Institute : Tropical Ecology
1 Presence of mucilage on aerial roots in Monteverde, Costa Rica Chase Kincaid Department of Agriculture and Natural Resources, Un iversity of Wisconsin Madison ___________________________________________________ ____________________ ABSTRACT: Many hemiepiphytes produce aerial roots and some ha ve mucilage on the growing tips of these roots. The purpose of this study was to determine if mucilage varies at different altitudes in the Monteverde Clo ud Forest in Costa Rica. Mucilage may serve to protect the roots from the dry environments, or from altit udes more prone to fungal infections since it has both h igh water storing capacities and anti-fungal proper ties. Transects were run along different altitudes, and s amples of plants mucilage were taken, measuring th e weight and length of the mucilage. Monstera was the most common plant with mucilage found in t he study and was found at all altitudes ranging from 1,400 m to 1,800 m. There were a total of 12 Monstera plants, two Pitcairnia plants, and one Philodendron plant with a total of 34 mucilaginous roots. Twent y-three of the mucilaginous aerial roots were found on the gen us Monstera (Araceae), 4 on Pitcairnia brittoniana (Bromeliaceae) and 7 on Philodendron (Araceae). No correlation was found between the we ight and length of mucilage, compared to altitude of all thr ee genera (Spearman rank correlation, N = 32; R2 = 0.135; p = 0.44 and N = 32; R2 = 0,86; p = .62, respectively). No correlation wa s also found for Monstera roots only, for weight and length compared to altit ude (Spearman rank correlation, N = 23; R2 = 0.10; p = .12 and N = 23; R2 = .004; p = .759, respectively). A trend could be seen in the total mucilage frequency for low and high altitudes for Monstera. In this case, 16 Monstera were found at low altitudes, and seven at high altitudes, but this difference was not statist ically significant (chi-squared test, x2 = 3.52, df = 1, p = 0.06). In conclusion, no altitudinal difference wa s found in mucilage size, suggesting genetic determ inants might be playing a role, but twice as many Monstera were found at low altitudes compared to high altitudes, although further studies need to be done to clarify the trend. RESUMEN: Algunas plantas hemiepfitas producen races areas y algunas de estas presentan muclago en puntas de estas races. El propsito de este estudio fue det erminar si el muclago vara a diferentes altitudes en el bosque nuboso de Monteverde en Costa Rica. El muc lago puede servir para proteger la raz contra la sequedad o contra infecciones por hongos en regione s de mayor altitud, ya que esta sustancia presenta tanto capacidad antifungca y de almacenamiento de agua. Se utilizaron transectos a diferentes altitudes, y se tomaron muestras de plantas con muclago, midiendo el peso y largo del mismo. Monstera fue la planta ms comn encontrada con muclago y fue encontrada a lo largo de todas las alturas desde 1400 m a 1800 m. Se encontraron un total de 12 plantas de Monstera 2 plantas de Pitcarnia y una planta de Philodendron (Arecaceae). No se encontr ninguna correlacin en tre el peso y largo del muclago, comparado con la altitud de los tres gneros (Correlacin de Spearma n, N = 32; R2 = 0.135; p = 0.44 y N = 32; R2 = 0,86; p = .62, respectivamente). No se encontr correlacin solamente para Monstera, para peso y largo comparado con la altitud (Correlacin de Spearman, N = 23; R2 = 0.10; p = .12 y N = 23; R2 = .004; p = .759, respectivamente). Una tendencia se observa en la f recuencia total de muclago para baja y mayor altit ud para Monstera En este caso, 16 plantas de esta especie se enco ntraron a menor altitud, y siete a mayor altitud, pero estas diferencias no son estadsticam ente significativas ( x2 = 3.52, df = 1, p = 0.06). En conclusin, no hay diferencias altitudinales in el tamao del muclago, sugieriendo que determinantes genticos pueden jugar un papel, pero de nuevo al e ncontrar ms plantas a menor altitud que a mayor altitud, se necesitan estudios posteriores para cla rificar est tendencia.
2 INTRODUCTION: Hemiepiphytes have developed strategies to prevent desiccation of their aerial roots while growing towards the ground and mucilage is believed to serve this purpose. (Gill 1969) Mucilage can commonly be found surrounding growing root tips. The mucilage has high water storage properties, which can help prevent de siccation by lengthening the time the aerial root has to absorb water. Darwin (1876) obse rved mucilage on Ficus ripens which remained wet for 128 days under hot and dry conditi ons. The mucilage has also shown to prevent fungal infections, as spores were found on the mucilage but never germinated (Ivey 1994). Mucilage is a polysaccharide that is secreted by Go lgi vesicles in cells near the growing tips of roots. The mucilage is believed to lubricate root tips as they move through the soil, and also serves the purpose of se nsing gravity. (Hopkins, 1995) Mucilage is thought to protect the root tip from de siccation and aid in nutrient absorption by allowing the roots to be in contact with more so il. (Russell, 1997) This mucilage is often invaded by bacteria, which may contribute to the roots by providing nutrients as metabolic byproducts in the soil and aerially. The mucilage, bacteria, and soil particle mixture is often called mucigel. (Hopkins, 1995) If mucilage acts as an anti-desiccant, more plants in dryer habitats would be expected to have mucilage and the amount of mucilag e would be expected to be greater. On the other hand, if mucilage protects roots from fungal infections, which are more likely in wet habitats, more plants in moister habi tats would be expected to have more and larger mucilage secretions. Therefore, I exami ne the size and frequency of mucilage on aerial roots along an altitudinal gradient near and in the Monteverde Cloud Forest of Costa Rica. Here, lower altitudes are on the seaso nal, dryer Pacific slope and represent areas likely to suffer some desiccation while highe r altitudes are generally wetter and less seasonal. The objective of this study was to determine if mu cilage production differs at varying altitudes. It was predicted that as altitud e decreases, number of plant species with mucilage would increase as the environment becomes drier. MATERIALS AND METHODS: This study was conducted in the Monteverde Cloud Fo rest Reserve in Costa Rica between October 28th and November 16th, 2008. Altitudes ranged from 1,400 m. to 1,800 m. The general approach was to conduct the experim ent by walking transects to observe/collect aerial roots with mucilage at diffe rent altitudes. Transects were run at 50 meter increments from 1,400 m to 1,800 m and altitu de was measured using a hand held watch altimeter. Transect lengths were 133 m and I looked for the aerial roots with mucilage as I walked. The trails used were at the Monteverde Biological Station and those of the Tropical Science Center (the Monteverd e Cloud Forest Reserve). Transects were run both on trail and off trail, although at h igh altitudes it was too difficult to run transects off trail. Once aerial roots with mucilage were found I record ed the number of mucilage masses per plant and the altitude the plant was fou nd. I then measured the length of the
3 mucilage on the root tip with a tape measure and co llected the mucilage from the plant, scraping off the mucilage into a cup to record its weight in grams using an electric, pocket-sized scale. I brought back plant samples t o be identified and also identified plant species in the field. Observations I recorded were : the mucilages weight, which plant species the mucilage occurs, altitude the mucilage was found at, and mucilage number per plant. RESULTS: A total of 125 transects were completed found a tot al of 34 aerial roots with mucilage. Twenty-three of the mucilaginous aerial roots were found on the genus Monstera and 4 on Pitcairnia brittoniana and 7 on Philodendron There were a total of 12 Monstera plants, two Pitcairnia plants, and one Philodendron plant. Comparisons were made on total aerial roots from t he three genera and also on Monstera alone since the majority of the data were on Monstera. There was no correlation between weight of the mucilage and alti tude for the total mucilaginous roots (Spearman rank correlation, N = 32; R2 = 0.135; p = 0.44), as well as for Monstera roots (Spearman rank correlation, N = 23; R2 = 0.10; p = .12). There was also no correlation between length of the mucilage and altitude for tot al roots (Spearman rank correlation, N = 32; R2 = 0,86; p = .62) and for Monstera roots specifically (Spearman rank correlation, N = 23; R2 = .004; p = .759). Monstera roots were analyzed in low and high altitude range s, with low altitudes ranging from 1,400 m to 1,600 m, and high altitudes ranging form 1,600 m to 1,800 m. Monstera were found throughout the 1400m 1600m range, but no mucilaginous roots were found between 1600 and 1770 m for Monstera Average weights for Monstera roots were compared at low and high altitudes and n o difference was found (MannWhitney U test, U = 40.5, p = 0.30, N1 = 16, N2 =7). (Fig. 1, a). I found no difference of lengths between low and high altitude mucilage of Monstera (Mann-Whitney U test, U = 41.5, p = 0.33, N1 = 16, N2 =7). (Fig 1, b) The total mucilage number for low and high altitud es for Monstera was 16 found at low altitudes, and seven at high altitudes (Fig. 2, a). Total mucilaginous roots were similar with 19 at high altitudes and 15 at low alt itudes (Fig. 2, b). There was no difference in Monstera mucilage between high and low altitudes (x2 = 3.52, df = 1, p = 0.06), although a trend can be seen with higher amo unts of mucilaginous roots at lower altitudes, with the p-value being very close to the acceptable p-value of 0.05. DISCUSSION: Monstera was the most prevalent plant in the study, therefo re would have been the most likely to show trends in the data. Monstera was found at both low and very high altitudes. No Monstera roots were found between 1600 m and 1770 m. Results comparing mucilage length and weight for bo th Monstera plants alone and total aroid species showed no correlation with altitude. Monstera plants may always produce the same amount of mucilage on an aerial ro ot, as the amount of mucus may be genetically determined. This does not support that the aerial roots in lowe r drier habitats would produce more mucilage per root to prevent des iccation. In all comparisons of
4 weight or length to altitude, there was a considera ble amount of overlap in the results with no statistical differences. The results showed some relationship in mucilage n umber of Monstera in low altitudes versus high altitudes. There was over twi ce as many roots with mucilage on them in lower elevations compared with high elevati on; supporting the prediction that there will be more mucilaginous aerial roots at low er elevations since the climate in the lower elevations is drier, and there would be more advantages for the plant to protect its aerial roots from desiccation. This appears to be a trend, but is not statistically significant as the p-value was over 0.05, though it was very cl ose at 0.06. This suggests that if there was a larger sample size, results may show a signif icant difference between low and high elevations. If the mucilage is serving two function s, fungal protection and desiccation prevention, there may be no difference in mucilage between low and high altitudes. Low altitudes may be more susceptible to desiccation si nce they are drier, but high altitudes may be more susceptible to fungal infections since they are wetter, so mucilage would be necessary in all ranges of altitudes. Further stud ies need to be done to clarify the trend seen by increasing sample sizes. ACKNOWLEDGEMENTS: I would like to thank my advisor Tania Chavarra fo r her help with my project statistics. Also to Alan and Karen Masters in their guidance throughout the proj ect. I am also grateful to the Monteverde Cloud Fo rest reserve and the Biological Station in the use of th eir trail systems to conduct my project. LITERATURE CITED: Darwin, C. 1876. The movements and habits of climbi ng plants. D. Appleton & Company, New York Gill, A. M. 1969. The ecology of an elfin forest in Puerto Rico: 6 aerial roots. Journal of the Arnold Arboretum 50: 197-209 Hopkins, G. W. 1995. Introduction to Plant Physio logy. John Wiley & Sons, Inc. Pp. 96, 275 Ivey, C. T. 1994. Experimental evidence concerning the function of mucilage on aerial root tips. Pp. 115-116 in Young, B. E. & Gilbert, G (eds). Tropical biology: an ecological approach. Organization for Tropical Studies, Durham NC. Russell, R. S. 1977. Plant Root Systems. Their Func tion and Interaction with the Soil. McGraw Hill, London. in Taiz, L. and Zeiger, E. 1991. Plant Phy siology. The Benjamin/ Cummings Publishing Company, Inc., Redwook City, California. Pp. 102 (a)
5 n nr r (b) n n r Figure 1. Average weight and length of mucilage and altitude are shown for Monstera at low (1,400 1,600 m) and high altitudes (1,600 1 ,800 m). (a) Avg. mucilage weight, standard deviation = .12 for low altitude, .42 for high altitude (Mann-Whitney U test, U = 40.5, p = 0.30, N1 = 16, N2 =7) (b) Avg. mucilage length, standard deviation = 2.6 for low altitude, 2.8 for high altitude (Mann-Whitney U test, U = 41.5, p = 0.33, N1 = 16, N2 =7).
6 (a) n n r n (b) n n rn Figure 2. Mucilage frequencies at low and high alti tudes. Low altitude range is 1,400 1,600 m and high altitude range is from 1,600 1,8 00 m. (a) Mucilage frequency of Monstera at low altitude (n =16), and high altitude (n = 7) (b) Total aroid mucilage frequency at low altitude (n =19), and high altitud e (n = 15).