1 Mycorrhizal abundance in aerial versus terrestrial roots among the climbing Araceae of the Monteverde Cloud Forest Sydney Glassman Department of Biology, University of Pennsylvania Abstract Climbing plants of the family Araceae are a prominent feature o f the Monteverde Cloud Forest in Costa Rica. Aerial and terrestrial roots were collected from two species of climbing aroids Syngonium sp A n = 15 and Philodendron aurantifolium n = 1 7 and analyzed for mycorrhizae presence and abundance. Evidence of m ycorrhizae infection was found in every plant sampled, and percent abundance of mycorrhizae in the aerial roots of Syngonium sp A ranged from 7.9 90%, while the mycorrhizal cover ranged from 5.3 38% in terrestrial roots. Mycorrhizal cover in the aerial roo ts of P. aurantifolium ranged from 8.2 57%, and from 4 33% in terrestrial roots. While a significant difference was not found between the aerial and terrestrial roots of P. aurantifolium Paired t test, t = 1.74, p = 0.10, mycorrhizae was significantly mo re abundant in the aerial roots of Syngonium sp A than in the terrestrial roots Paired t test, t = 3.11, p = 0.00 8 . Additionally, individuals of the species Syngonium sp A experienced on average a greater percentage of mycorrhizal infections in their aer ial roots than did P. aurantifolium individuals Unpaired t test, t = 2.19, p = 0.036. No difference in mycorrhizal infection was detected in terrestrial roots Unpaired t test, t = 0.19, p = 0.84 9 . This report confirms the presence of mycorrhizae in two species of tropical climbing aroids, and suggests that aerial roots of an individual climbing plant may harbor on average more mycorrhizal infections than their respective terrestrial roots. Resumen Las p lantas escaladoras de la familia Araceae son una caracterÃstica prominente del Bosque Nuboso de Monteverde en Costa Rica . Las raÃces aÃ©reas y terrestres fueron tomadas de dos especie s de arÃ¡ceas epÃfilas Syngonium sp. A N = 15 y Filodendro aurantifolium N = 17 y analizada s para medir la presencia de micorrizas y su abundancia . La evidencia de la infecciÃ³n de m icorrizas fue encontrada en cada planta probÃ³ , y por ciento abundancia de micorrizas en las raÃces aÃ©reas de Syngonium especia A el promedio de micorrizas fue de 7.9 90%, mien tras la cubierta de micorrizas en raÃces terrestres fue 5.3 38% . La cubierta de micorrizas en las raÃces aÃ©reas de P. aurantifolium recorriÃ³ de 8.2 57%, y de 4 33% en raÃces terrestres . Mientras no fue encontrada una diferencia significativa entre la s raÃces aÃ©reas y terrest res de P. aurantifolium la T prueba pareada , T = 1,74, P = 0 ,10, micorrizas fue apreciablemente mÃ¡s abundante en las raÃces aÃ©reas de Syngonium sp A que en l as raÃces terrestres la T prueba pareada , T = 3,11, P = 0 , 008. Adicionalmente , los individuos d e la especie Syngonium sp A experimentar o n en promedi o un porcentaje mÃ¡s grande de infecciones de m icorrizas en sus raÃces aÃ©reas que hizo l os individuos de P. aurantifolium la T prueba Irreparada, T = 2,19, P = 0,036. Ninguna diferencia en la infecciÃ³n de micorrizas fue discernida en raÃces terrestres la T prueba i rreparada , T = 0,19, P = 0,849. Este info rme confirma la presencia de micorrizas en dos especie s de arÃ¡ceas escaladoras tropicales , y sugiere que las raÃces aÃ©reas de un individuo planta escalad ora puede abrigar en el promedio mÃ¡s infecciones de m icorrizas que sus raÃces terrestres respectivas.
2 Introduction Mycorrhizae are symbiotic fungi associated with the roots of vascular plants Lesica and Antibus 1990. The most common mycorrhizae ar e vesicular arbuscular VAM obligately symbiotic fungi in the order Glomales Smith and Read 1997. Mycorrhizal fungi benefit their host plants by enhancing the physiologically active area of the root system and increasing the plantÂ€s ability to capture w ater and nutrients Rains et al. 2003. VAM are widespread and common in many plants all over the world, especially in the tropics Smith and Read 1997. As important as mycorrhizal symbionts may be for plant growth, environmental conditions must be corre ct for a mycorrhiza to develop because they prefer low nutrient soils Alexopoulos et al. 1996. Thus, not all vascular plants may harbor mycorrhizal infections. Arbuscular mycorrhizae have been observed in epiphytic aroids in the lower montane cloud fore st canopy of Monteverde Rains et al. 2003, an area that is characterized by an unmatched abundance of moss, epiphytes, and tree trunk climbers Haber 2000. Climbers are plants that cannot support themselves in an erect position at maturity, and epiphyte s are plants dependent on trees and other plants for mechanical support but not nutrition Ingram 2000. While the presence of mycorrhizae in epiphytic aroids has been noted, infections in climbing aroids have yet to be studied. Most species of herbaceous tree trunk climbing epiphytes in the Monteverde cloud forest are of the family Araceae, which includes 32 species of the Philodendron , Monstera and Syngonium genera Haber 2000. Araceae is a primarily tropical and subtropical monocot family Mabberley 19 87, with a distinctive inflorescence called a spadix, covered in a bract called a spathe Zuchowski 2005. Aroids have also evolved a plethora of growth forms . They can be found as scrambling shrubs, climbers with aerial roots, enormous herbs, and occasio nally as a true epiphyte or in the rare case, as a free floating aquatic plant Mabberley 1987 . Of the 80 species of aroids known in Monteverde, 44 are vines or hemiepiphytes Haber 2000. Although VAM fungi are widely regarded as mutualistic and even ind ispensable symbionts, their extensive use of plant carbohydrates makes the continuum to parasitism unclear Johnson et al. 1997. Because of this, a plant may preferentially allow infections in roots with less access to nutrient rich substrates . Climbing plants possess terrestrial roots, but sequester additional nutrients from ambient mist via aerial roots, which are present along the stems, positioned at nodes Hinchee 1981 . Thus, aerial roots of an individual may contain more mycorrhizae than their terr estrial counterparts as they would presumably have less access to nutrients than those rooted in the soil. The goal of this study is to determine the incidence of mycorrhizal infections in climbing species of aroids, which is a new area of inquiry. Addit ionally, I am interested in the potential for differential abundance of mycorrhizae in aerial versus terrestrial roots. Due to their variation in location and access to nutrients, I expected a difference in the abundance of mycorrhizae between terrestria l and aerial roots. I predicted that aerial aroid roots would have a higher abundance of mycorrhizae as they have less constant access to nutrients and would therefore be more likely to invest in the costly symbiont.
3 Materials and Methods This study wa s conducted in lower montane rain forest sensu Holdridge, 1967 located behind the EstaciÃ³n BiolÃ³gica in Monteverde, Costa Rica elevation 1500 1600 m. I analyzed the aerial and terrestrial roots of two different species of climbing aroids, Philodendron aurantifolium n = 17 and an unidentified species of Syngonium sp A n = 15 . Both species of aroids were chosen due to their abundance in the cloud forest and varying growth morphologies. Philodendron aurantifolium was more often found climbing on trees , while Syngonium sp A individuals were more often found climbing on the ground. However, individuals from both species were found in both environments. Samples were collected at the end of the dry season, from April 11 May 5, 2007. Once collected, the roots were given an initial rinse in water to remove excess dirt and leaf matter. Next, the samples were soaked in 10% KOH for one to seven days. The roots were then removed from KOH and submerged in a 1% HCL solution for one hour in order to enhance th e efficiency of dye absorption. After soaking in the acid solution, the roots were put in a solution containing a 4:2:1 ratio of 50% glycerol, 1% HCL, and 0.05% Trypan blue dye for about twenty five minutes. Stained roots were cut into very thin cross se ctions, mounted onto slides, and observed under a 40x field view with a compound light microscope. Mycorrhizae presence or absence was recorded for every root sample. Pictures of each sliced and stained root cross section were taken with an Olympus 7.1 me ga pixel digital camera with an attached microscope adapter for use in quantification. Mycorrhizae abundance was recorded as the number of cross hairs covering mycorrhizae divided by the number of cross hairs in the entire field of view using a transparent 1.0 cm x 1.0 cm grid sheet. Several aerial and terrestrial roots were used for each plant. Three to seven pictures from different sections of each aerial and each terrestrial root sample were averaged to obtain more accurate abundance estimates across an entire root. The data were analyzed for deviation from a normal distribution using the Shapiro Wilk W Test. I performed a paired t test for each species to determine if mean percent abundance of mycorrhizae was significantly higher in the aerial or terres trial roots. I checked for the effect of species on the mean percent abundance of mycorrhizae using an unpaired t test. I tested for effects of habit on mycorrhizal abundance using Wilcoxon sign rank test. Results Mycorrhizal infections were observed in all 32 individuals sampled. The percent abundance of mycorrhizal cover in the aerial roots of Syngonium sp A ranged from 7.9 90%, and from 5.3 38% in terrestrial roots Appendix 1. Mycorrhizal cover in the aerial roots of P. aurantifolium ranged from 8. 2 57%, while terrestrial roots ranged from 4 33% Appendix 2. All of the data were normally distributed Shapiro Â Wilk W Test, Syngonium sp A aerial: w = 0.93, p = 0.07; Syngonium sp A terrestrial: w = 0.93, p = 0.26; Philodendron aurantifolium aerial: w = 0.923, p = 0.19; P. aurantifolium terrestrial, w = 0.92, p = 0.149. Because the data did not differ significantly from a normal distribution, I tested for a difference in mycorrhizal abundance between aerial and terrestrial roots. While
4 aerial roots w ere not found to differ appreciably from the terrestrial roots of P. aurantifolium Paired t test, t = 1.74, p = 0.10, a difference was found in the mycorrhizal abundance of Syngonium sp A Figure 2 . Mycorrhizae were significantly more abundant in the ae rial roots of Syngonium sp A than in terrestrial roots Paired t test, t = 3.11, p = 0.008 Figure 1. FIGURE 1: Mean mycorrhizal abundance percent of grid cells occupied; with standard error bars in the aerial versus terrestrial roots in 15 individua ls Syngonium sp A Araceae in the Monteverde cloud forest of Costa Rica. Mycorrhizae were significantly more abundant in aerial than terrestrial roots . 0 10 20 30 40 50 60 aerial terrestrial Root type Mean Mycorrhizal Abundance %
5 FIGURE 2: Mean percent abundance of mycorrhizae in the terrestrial and aerial roots of 17 individua ls of Philodendron aurantifolium Araceae in the Monteverde cloud forest of Costa Rica. There was no significant difference in the mycorrhizae cover between aerial and terrestrial roots . Standard error bars are shown. Additionally, i ndividuals of the s pecies Syngonium sp A experienced on average a greater percentage of mycorrhizal infections in their aerial roots than did P. aurantifolium individuals Unpaired t test, t = 2.19, p = 0.036 Figure 4. Although the abundance of mycorrhizae in aerial roo ts differed between species, no significant difference was detected between terrestrial roots Unpaired t test, t = 0.19, p = 0.8 49 Figure 3. 0 5 10 15 20 25 30 35 aerial terrestrial Root type Mean Mycorrhizal Abundance %
6 FIGURE 3: Mean mycorrhizal abundance percent of grid cells occupied; standard error bars shown in the ter restrial roots of Philodendron aurantifolium n = 17 and Syngonium sp A n = 15 in the Monteverde cloud forest of Costa Rica. Mycorrhizae abundance in terrestrial roots did not differ significantly between species . 0 5 10 15 20 25 Philodendron aurantifolium Syngonium Aroid Species Mean mycorrhizal Abundance %
7 FIGURE 4: Mean mycorrhizal percen t abundance in the aerial roots of Philodendron aurantifolium n = 17 and Syngonium sp A n = 15 in the Monteverde cloud forest of Costa Rica. Aerial roots of Syngonium sp A had significantly more mycorrhizae than aerial roots of P. aurantifolium . Stan dard error bars are shown. The plants I sampled from were either found climbing on the ground, on a tree, hanging from a tree, or climbing on a stump or dead log. To determine if proximity to the ground affected mycorrhizae, I separated the plants into e ither ground or climbing habits. No significant difference was found in mycorrhizal abundance in terrestrial or aerial roots between the various growth habits of either aroid species Wilcoxon sign rank test, Philodendron aurantifolium aerial: z = 1.59, p = 0.11; P. aurantifolium terrestrial: z = 1.06, p = 0.288; Syngonium sp A aerial: z = 0.67 , p = 0.50 1 ; Syngonium sp A terrestrial: z = 0.43 , p = 0.66 8 Figures 5 and 6. Thus habit was not found to have an effect on mycorrhizal abundance in aerial or terr estrial roots in either species. 0 5 10 15 20 25 30 35 40 45 50 Philodendron aurantifolium Syngonium Aroid Species Mean Mycorrhizal Abundance %
8 FIGURE 5: Mean mycorrhizal percent abundance with standard error bars in aerial and terrestrial roots of Syngonium sp A with respect to growth habit. Fifteen individuals were sampled in the Monteverde Cloud Forest, Cos ta Rica. Ten individuals were found climbing on the ground, five individuals were found climbing on a tree or dead log. No effects of habit on mycorrhizal abundance were found . 0 10 20 30 40 50 60 70 ground tree ground tree Aerial Terrestrial Mean Mycorrhizal Abundance % n = 10 n = 10 n = 5 n = 5
9 FIGURE 6: Mean mycorrhizal percent abundance with standard error bars in aerial and terrestrial roots of Philodendron aurantifolium with respect to growth habit. Seventeen individuals were sampled in the Monteverde Cloud Forest, Costa Rica. Seven individuals were found climbing on the ground, and nine individuals were climbing on trees or dead logs. No effects of habit on mycorrhizal abundance were found . Discussion My study confirms the presence of mycorrhizae in two species of climbing aroids. Current knowledge of the distribution of arbuscular mycorrhizae in natural areas remains limited; in fact, only a small fraction of the known monocot species have been reviewed for mycorrhizal association Santos et al. 2000. Cloud forest conditions such as low phosphorous concentration, elevated moisture level, and the presence of potential biotic spore dispersers may be particularly conducive to mycorrhizal colonization in climbing plants Rains et al. 2003. My data show that mycorrhizae are more abundant in the aerial roots of Syngonium sp A than P. aurantifolium, and mycorrhiz ae can be found at higher abundances in the aerial roots of Syngonium sp A than in the terrestrial roots. The developmental and growth processes in shoots are much better known than those of roots. The aerial root in particular is a developmental system t hat is often overlooked Hinchee 1981. However, my results show that aerial roots may be essential to enhancing nutrient uptake in climbing plants. Aerial roots sequester nutrients and water from ambient mist and debris. Many are able to gain more acce ss to nutrients by burrowing in mossy mats 0 5 10 15 20 25 30 35 40 45 ground tree ground tree Aerial Terrestrial Mean Mycorrhizal Abundance % n = 9 n = 9 n = 7 n = 7
10 on tree trunks, eventually becoming terrestrial, picking up dead leaf matter, or perhaps by increasing their rate of infection by symbiotic fungi. Because mycorrhizae are costly for plants to support, one would expect plants to only allow fungal infections in roots needing extra access to nutrients and water. A symbiosis with mycorrhizae may bring these necessary nutritional benefits. One study estimated that external hyphae of VAM fungi can deliver up to 80% o f a plantÂ€s phosphorous requirements and 25% of a plantÂ€s nitrogen requirements Maschner & Dell 1994. However, a t high fertility levels some plants may reject mycorrhizal infection, choosing rather to employ more root hairs than pay the carbon cost of t he fungi Janos 1983. Thus, aerial roots may harbor more mycorrhizae than terrestrial roots because terrestrial roots have access to soil nutrients and may thus shed excess mycorrhizae. Surprisingly, while individuals of Syngonium sp A followed the expect ed pattern, root location did not appear to affect mycorrhizal abundance in the roots of P. aurantifolium individuals. Philodendron aurantifolium appear to overall invest less in their aerial roots. The se species belong to different genera, which could a ffect their ability to sequester nutrients. Philodendron aurantifolium individuals appear to have thicker stems on average than the Syngonium sp A . Perhaps they have an increased capacity to transport water and nutrients sequestered from the terrestrial r oots than Syngonium sp A individuals, causing less dependence on their aerial roots for nutrition . Furthermore, the presence of aerial roots appeared to be highly variable ; many individuals lacked aerial roots completely or all were dedicated to structura l support. It is also possible that the P. aurantifolium individuals simply could not afford the extra mycorrhizae. The presence of mycorrhizae in terrestrial roots did not differ between species. This finding is not surprising as VAM are generally conside red ubiquitous in terrestrial soils Janos 1993. As all terrestrial roots have the same access to the nutrient poor lower montane cloud forest soils, they experience no significant difference in nutrient availability. Similar vectors of spore dispersal c ould potentially reach all species of terrestrial roots, while spore dispersers may have more difficulty reaching aerial roots of varying levels of accessibility. Thus it makes sense that aerial roots, with their differential access to nutrients and spore dispersers, show a difference in percent mycorrhizal infection between species while terrestrial roots do not. An ecological factor that could potentially contribute to differences in mycorrhizal abundance is the variation in growth habit of individual cl imbers. A plantÂ€s substrate could potentially affect the need for mycorrhizae or access of roots to spore dispersers. However, growth habit was not found to affect significantly the percent of mycorrhizal coverage in either terrestrial or aerial roots. Th is apparent lack of difference in mycorrhizal infection could potentially be due to the special mobility of climbing plants. The climbing habit of the Araceae is expressed in elongated and relatively unbranched stems, which results in a plant whose one ap ical shoot meristem is displaced relatively rapidly through the forest, while the trailing stem eventually senesces behind it Ray 1992. This type of growth results in a mobility that is unique to plants, which are usually considered sessile organisms. For instance, aroids are able to orient themselves towards trees through skototropism Strong and Ray 1975 in Ray 1992. A plant I found climbing on the ground during the dry season could very well make it to a tree by the wet season. Therefore, mycorrhiza l infection may not differ significantly across species and
11 root types based on growth habit because that growth habit is most likely an ephemeral condition. Climbers are abundant in tropical forests, and mycorrhizae may very well be essential to their gro wth. Mycorrhizal fungi have been shown to almost completely close tropical rain forest nutrient cycles by their efficient uptake of nutrients from soil in addition to their advantageous position for scavenging nutrients from dying roots Janos 1983, from C .F. Jordan 1985. Although they may be a huge factor contributing to the efficiency and productivity of tropical forests, we often underestimate the ecological complexity of mycorrhizal systems Johnson et al. 1997. A study in the nutritional and distri butional differences in root substratum would be helpful for the future. Investigating plant physiology with respect to patterns of nutrient appropriation and transport would help explain why species differ in their patterns of mycorrhizal infection, and p erhaps further elucidate the specifics of plant VAM interactions. Much controversy remains even over the basics of mycorrhizal identification, although some hope lies in the new molecular techniques being developed Rowe and Pringle 2005. Understanding w hy aerial roots may harbor more mycorrhizal infections than their terrestrial counterparts can have implications in the evolution of the mycorrhizal plant mutualism, in addition to adding to the basic knowledge of how mycorrhizae function. Mycorrhizae hav e the potential to impact hugely tropical landscapes; because of this, more research on these influential fungi is warranted. Acknowledgments: Thank you so much to Karen Masters, Tom Mcfarland, Cam Pennington, all of whom were essential to the completion of this report. Thank you to Laura Garrison for helpful comments and revisions. Also thanks to Bill Haber and Willow Zuchowski for help in plant identification, and Estacion Biologica de Monteverde for use of the forest. Literature Cited Alexopoulos, C.J., C.W. Mims, and M. Blackwell. 1996. Introductory Mycology. D. Harris, ed. John Wiley and Sons, United States. Pp. 515. Allen, M.F., E. Rincon, E.B. Allen, P. Huante and J.J. Dunn. 1993. Observations of canopy bromeliad roots compared with plants ro oted in soils of a seasonal tropical forest, Chamela, Jalisco, Mexico. Mycorrhiza 4: 27 28. Eaton, D.A.R. 2005. Mycorrhizal fungi in aerial and terrestrial roots of an epiphytic and two terrestrial species of Orchidaceae. CIEE Fall 2005. Haber, W. 2000. Plants and Vegetation. In: Monteverde: Ecology and Conservation of a tropical cloud forest. Nadkarni N. and N.T. Wheelwright, ed. The Oxford University Press, New York. pp. 39 40, 54. Hinchee, M.A.W. 1981. Morphogenesis of Aerial and Subterranean Roots i n Monstera deliciosa . Botanical Gazette 142: 347 359. Ingram, S. 2000. Epiphytes. In: Monteverde: Ecology and Conservation of a tropical cloud forest. Nadkarni N. and N.T. Wheelwright, ed. Oxford University Press, New York. pp. 72 73. Janos, D.P. 1993 . Vesicular arbuscular mycorrhizae of epiphytes. Mycorrhiza 4:1 4. Janos, D.P. 1983. Vesicular Arbuscular Mycorrhizal Fungi . In: Costa Rica Natural History . D.H. Janzen, ed. The University of Chicago press, Chicago, IL. pp. 340 345. Johnson, N.C., J.H. Graham, and F.A. Smith. 1997. Functioning of Mycorrhizal Associations along the Mutalism Parasitism Continuum. New Phytologist 135: 575 586. Jordan, C.F. 1985. Nutrient Cycling in Tropical Forest Ecosystems. John Wiley & Sons Ltd., Great Britain.
12 Lee, Y. C. Mycorrhizae concentration and fitness of canopy orchids in the Cloud forest of Monteverde, Costa Rica. CIEE Fall 2006. Lesica, P. and R.K. Antibus. 1990. The Occurrence of Mycorrhizae in Vascular Epiphytes of Two Costa Rican Rain Forests. Biotropica 22: 250 258. Mabberley, D.J. 1987. The Plant Book: A portable dictionary of the higher plants. Cambridge University Press, Great Britain. pp. 39. Marschner, H., and B. Dell. 1994. Nutrient uptake in mycorrhizal symbiosis. Plant and Soil 159: 89 102. Rains , K.C., N.M. Nadkarni, and C.S. Bledsoe. Epiphytic and terrestrial mycorrhizas in a lower montane Costa Rican cloud forest. Mycorrhiza 13: 257 264. Ray, T.S. 1992. Foraging Behavior in Tropical Herbaceous Climbers Araceae. The Journal of Ecology 80: 1 89 203. Rowe, A.R. and A. Pringle. 2005. Morphological and molecular evidence of arbuscular mycorrhizal fungal associations in Costa Rican epiphytic bromeliads. Biotropica 37: 245 250. Santos, B.A., G.A. Silva, L.C. Maia, and M.V. Alves. 2000. Mycorrhiza e in Monocotyledonae of Northeast Brazil: subclasses Alismatidae, Arecidae, and Zingiberidae. Mycorrhiza 10: 151 153. Smith, S.E. and D.J. Read. 1997. Mycorrhizal Symbiosis . Academic Press, London. Zuchowski, W. 2005. A Guide to Tropical Plants of Costa Ri ca. Zona Tropical Publication, Costa Rica.
13 Appendix 1 Abundance of mycorrhizae found in aerial and terrestrial roots of Syngonium sp A Araceae. Collected April 11 May 5, 2007 in the Monteverde cloud forest of Costa Rica. Individual Aerial roots % abundance Terrestrial roots % abundance 1 7.9 38 2 33 22 3 82 22 4 28 24 5 22 6.8 6 25 28 7 46 8.0 8 31 7.5 9 53 14 10 86 6.0 11 34 33 12 39 29 13 90 17 14 43 13 15 15 5.3 Appendix 2 Abundance of mycorrhiza e found in aerial and terrestrial roots of Philodendron aurantifolium Araceae. Collected April 11 May 5, 2007 in the Monteverde cloud forest of Costa Rica. Individual Aerial roots % abundance Terrestrial roots % abundance 1 42 33 2 27 6 3 14 18 4 15 6.4 5 8.2 25 6 37 28 7 0 26 8 54 4 9 14 29 10 11 20 11 39 19 12 57 16 13 42 33 14 15 6 15 32 13 16 18 9.6 17 14 7.6
14 Appendix 3 Sample mycorrhizae pictures taken from Oympus 7.1 camera with microscope adapter under 40x magnification with compound microscope . A. Philodendron aurantifolium terrestrial 29A terrestrial 29% average abundance B. Syngonium sp A terrestrial 3C terrestrial 22% average abundance
15 C . Syngonium sp A aerial 13 C aerial 90 % average abundance D. Syngonium sp A terrestrial 13 C terrestrial 17% average abundance
16 E. Syngonium sp A aerial 8C aerial 82% average abundance D. Syngonium sp A terrestrial 5C terrestrial 8% average abundance
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La abundancia de micorrizas en las races areas versus terrestres en medio del Araceae trepadora del Bosque Nuboso de Monteverde
Mycorrhizal abundance in aerial versus terrestrial roots among the climbing Araceae of the Monteverde Cloud Forest
Climbing plants of the family Araceae are a prominent feature of the Monteverde Cloud Forest in Costa Rica. Aerial and terrestrial roots were collected from two species of climbing aroids Syngonium sp A (n = 15) and Philodendron aurantifolium (n = 17) and analyzed for mycorrhizae presence and abundance. Evidence of mycorrhizae infection was found in every plant sampled, and percent abundance of mycorrhizae in the aerial roots of Syngonium sp A ranged from 7.9-90%, while the mycorrhizal cover ranged from 5.3-38% in terrestrial roots. Mycorrhizal cover in the aerial roots of P. aurantifolium ranged from 8.2-57%, and from 4-33% in terrestrial roots. While a significant difference was not found between
the aerial and terrestrial roots of P. aurantifolium (Paired t-test, t = 1.74, p = 0.10), mycorrhizae was significantly more abundant in the aerial roots of Syngonium sp A than in the terrestrial roots (Paired t-test, t = 3.11, p = 0.008). Additionally, individuals of the species Syngonium sp A experienced on average a greater percentage of mycorrhizal infections in their aerial roots than did P. aurantifolium individuals
(Unpaired t-test, t = 2.19, p = 0.036). No difference in mycorrhizal infection was detected in terrestrial roots (Unpaired t-test, t = 0.19, p = 0.849). This report confirms the presence of mycorrhizae in two species of tropical climbing aroids, and suggests that aerial roots of an individual climbing plant may harbor on average more mycorrhizal infections than their respective terrestrial roots.
Las plantas escaladoras de la familia Araceae son una caracterstica prominente del Bosque Nuboso de Monteverde en Costa Rica.
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