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Mycorrhizae concentration and fitness of canopy orchids in the cloud forest of Monteverde, Costa Rica

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Title:
Mycorrhizae concentration and fitness of canopy orchids in the cloud forest of Monteverde, Costa Rica
Translated Title:
La concentración de Mycorrhizae y la aptitud de las orquídeas de dosel en el bosque nuboso de Monteverde, Costa Rica ( )
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Book
Language:
English
Creator:
Lee, You-Young Clover
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Subjects / Keywords:
Mycorrhizal fungi   ( lcsh )
Orchids   ( lcsh )
Inflorescences   ( lcsh )
Hongos Mycorrhizal
Orquídeas
Inflorescencias
Tropical Ecology 2006
Plant fitness
Ecología Tropical 2006
Aptitud de la planta
Genre:
Reports   ( lcsh )
Reports

Notes

Abstract:
Orchids require the presence of mycorrhizal fungi in their root systems to germinate, but the importance of fungi after germination is the focus of this investigation. The purpose of this study was to examine whether increasing the coverage of mycorrhizal fungi increases overall fitness and productivity of individual orchids. Orchids of two species Masdevalia chasei and Trichosalpinx memor were collected from cloud forest tree canopies and their fitness and infection levels were estimated. The fitness of each individual was measured here as number of leaves, number of inflorescences, length of longest leaf, length of longest stem. The percent coverage of mycorrhizae was determined by the amount of area on a cross section of a root sample covered by fungi divided by the total surface area of each cross section. The results showed that the amount of mycorrhizal fungi is not correlated with orchid fitness or productivity. There was no significant difference between the mean percent coverage between the two orchid species (t-test, t = 0.08, p = 0.94, df = 43). The importance of mycorrhizal fungi to epiphytic orchids in the cloud forests of Monteverde may be important and possibly even critical, but not precisely correlated with fitness.
Abstract:
Las orquídeas requieren la presencia de hongos micorrícicos en sus raíces para germinar, pero la importancia de estos hongos después de la germinación es el enfoque de esta investigación. El propósito de este estudio fue examinar si aumentando el número de hongos micorrícicos, la salud y la productividad de las orquídeas individuales aumentan.
Language:
Text in English.
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Born Digital

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Mycorrhizae concentration and fitness of canopy orchids in the cloud forest of Monteverde, Costa Rica
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Orchids require the presence of mycorrhizal fungi in their root systems to germinate, but the importance of fungi after germination is the focus of this investigation. The purpose of this study was to examine whether increasing the coverage of mycorrhizal fungi increases overall fitness and productivity of individual orchids. Orchids of two species Masdevalia chasei and Trichosalpinx memor were collected from cloud forest tree canopies and their fitness and infection levels were estimated. The fitness of each individual was measured here as number of leaves, number of inflorescences, length of longest leaf, length of longest stem. The percent coverage of mycorrhizae was determined by the amount of area on a cross section of a root sample covered by fungi divided by the total surface area of each cross section. The results showed that the amount of mycorrhizal fungi is not correlated with orchid fitness or productivity. There was no significant difference between the mean percent coverage between the two orchid species (t-test, t = 0.08, p = 0.94, df = 43). The importance of mycorrhizal fungi to epiphytic orchids in the cloud forests of Monteverde may be important and possibly even critical, but not precisely correlated with fitness.
Las orqudeas requieren la presencia de hongos micorrcicos en sus races para germinar, pero la importancia de estos hongos despus de la germinacin es el enfoque de esta investigacin. El propsito de este estudio fue examinar si aumentando el nmero de hongos micorrcicos, la salud y la productividad de las orqudeas individuales aumentan.
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Mycorrhizal fungi
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Inflorescences
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Orqudeas
Inflorescencias
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Plant fitness
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Aptitud de la planta
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Reports
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CIEE
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Mycorrhizae concentration and fitness of canopy orchids in the Cloud Forest of Monteverde, Costa Rica You-Young Clover Lee Department of Neuroscience and Behavior, Mount Holyoke College ________________________________________________________________________ ABSTRACT Orchids require the presence of mycorrhizal fungi in their root systems to germinate, but the importance of fungi after germination is the focus of this investigation. The purpose of this study was to examine whether increasing the coverage of mycorrhizal fungi increases overall fitness and productivity of individual orchids. Orchids of two species Masdevalia chasei and Trichosalpinx memor were collected from cloud forest tree canopies and their fitness and infection levels were estimated. The fitness of each individual was measured here as number of leaves number of inflorescences, length of longest leaf, length of longest stem. The percent coverage of myco rrhizae was determined by the amount of area on a cross section of a root sample covered by fu ngi divided by the total surface area of eac h cross section. The results showed that the amount of mycorrhizal fungi is not correlated with orchid fitness or productivity. There was no significant difference between the mean percent coverage between the two orchid species (t-test, t = 0.08, p = 0.94, df = 43). The importance of mycorrhizal fungi to epiphytic orchids in the cloud forests of Monteverde may be important and possibly even criti cal, but not precisely corr elated with fitness. RESUMEN Las orqudeas requieren la presencia de hongos mi corriticos en sus raices para germinar, pero la importancia de estos hongos despus de que la germinacin esel foco de esta investigacin. El propsito de este estudio fue examinar si aumentando el nmero hongos micorrhiticos la salud y productividad de orquideas individuales aumentan. La s orqudeas de dos especies Masdev alia chasei y Trichosalpinx memor fueron escogirlas del dosel del bosque nuboso y sus nive les de la salud y la infeccin fueron estimados. La salud de cada individuo fue medida como el nmero de hojas, el nmero de inflorescencias, la longitud de hoja ms larga, la longitud del tallo ms largo. El por porcentaje dealcance de las micorrhizas fue determinado por la cantidad de rea en una seccin transversal de un a muestra de raz cubierto por hongos dividido por el rea total de cada seccin transversal. Los resultados mostraron qu e la cantidad de hongos de micorrhizas es la correlacionnda con la salud de la orqudea ni con la productividad. No hubo diferencia significativa entre el porcentaje de alcance entre la dos especie de orqudea (la T-prueba, T = 0,08, P = 0,94, df = 43). La importancia de hongos micorrhizas a orqudeas de epiphytic en los bosques nuboasos de Monteverde puede ser importante y po siblemente an crtica, pero no se correlaciono precisamente con la salud de la orquidea. INTRODUCTION 1

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The Family Orchidaceae is one of the largest angiosperm fa milies (Dressler 1990). This family has large variations in floral featur es and life forms (Dressler 1990) but despite great variability orchids require symbiosis with mycorrhizal fungi for seed germination (Walter 1983). The orchid-fungi association has coevolved to improve the fitness of both the orchid and the fungi by the reciprocal exchan ge of mineral and organic resources (Johnson et al. 1997). Orchid seeds lack nutrient storage ca pabilities (Dressler 1990). Intracellular hyphal coils, pelatons, are sacs filled w ith water and organic minerals created by mycorrhizae. The pelotons are digested by th e orchid, allowing the transfer of nutrients from the mycorrhizal fungi to orchid (Bayman et al. 2002). This is why orchid embryos will not develop unless they are occupied by fungi Little is known about the factors that promote orchid germination. Fungi have the capability of changi ng insoluble complex carbohydrates into digestible simple sugars that will provide suitable food supply for the germinating orchid (Walter 1983). The a bundance of mycorrhizal fungi in adult epiphytic orchids can vary from very low to very high (Janos 1983). It is unclear from past studies if the abundance of mycorrhizal fungi present is determined by the orchid species, the availability of the well-matched fungi, or ozone depletion (Bayman et al. 2002). The factors that seem to mediate the orchid-fungi symb iosis are biotic and abiotic factors of the environment and the comm unity composition (Johnson et al. 1997). Truly non-mycorrhizal orchid species and ge nera are rare in nature and the great majority of plants are dependent on mycorrh izal fungi to some degree (Johnson et al. 2002). In addition to being a major mineral s upplier, fungi may also facilitate free water absorption. In adult orchids the mycorrhizal fungi provide the plant with soil-derived 2

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mineral nutrients such as nitrogen or phosphor ous (Dressler 1990). Another advantage of the presence of mycorrhi zal fungi is that they dissuade environmental parasites. A study provided evidence that the mere presence of mycorrhizal fungi in adult orchid roots discourages parasitic inf ection (Bayman et al. 2002). The purpose of this study is to the test if there is any correlation between the percent coverage of mycorrhizal fungi and the overall fitness of the individual orchid. In past research, fitness has been defined and determined by survival, fecundity and biomass changes at the scale of an individual orch id (Johnson 1997). In this particular study, estimates of fitness will be the number of leav es of an individual pl ant, number of total leaves (dead and alive), number of inflores cences, total number of inflorescences (dead and alive), length (cm) of longest leaf and length (cm) of longest stem. It is predicted that the higher the pe rcent coverage, the greater the number of current leaves and past leaves number of current inflorescen ces and past inflorescences, and the length of the longest stem and longest leaf will be greater than orchids with a lesser percent coverage of fungi. Overall, the plant will be more fit with greater mycorrhizal fungi coverage on its roots b ecause of fungis parasite protection and allowing reciprocal exchange of organic and mineral resources. MATERIALS AND METHODS This study was conducted in two po pulations of orchid species: Masdevalia chasei (n = 25), and Trichosalpinx memor (n = 20). Both species of orchids were chosen for this study because of their abundance in the cl oud forests of Monteverde, Costa Rica. Masdevalia chasei was collected in the top of a ca nopy tree at 1545 m in altitude, and T. 3

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memor was collected in the top of a different canopy tree at 1745 m in altitude. This study was conducted at the end of the rai ny season November, 2006. Both species of orchids are endemic to Monteverde along w ith other tropical regions of the world (Hammel et al. 2003). Only adult specimens of both species were included in the experiment. In order to determine the fitne ss level of an individual orchid, the number of past and current inflorescences was counted. An adult specimen is defined as being able to reproduce. Fitness correlates for M. chasei were slightly different from T. memor. Masedevalia chasei has clearly differentiated stems and leaves, T. memor s stem and leaves are fused. Therefore stem length and leaf length for T. memor were counted as one fitness correlate. It would be impossible to measure the stem and leaves separately for T. memor because it is unfeasible to differentiate Therefore the fitness correlate for T. memor, length of longest leaves and longest st em was fused into one fitness category. A root section of 3 cm of the orchid was cut and placed in 10% KOH solution for 24 hours to clean off sediment on the root. After 24 hours, the KOH was discarded and the root sections immersed in a 1% HCL solution for one hour. The acidity of the HCL allowed the roots to absorb the dye efficiently at a faster rate. A 4:2:1 ratio of 50% glycerol, 1% HCL and 0.05% of Trypan blue dye was added in place of the 1% HCL. After approximately 20 minutes, thin cross-sec tions of the root were sliced and placed onto a microscope slide and observe d under a 100x field of view. Pictures of root cross section were ta ken with an Olympus 7.1 mega pixel digital camera, with an attached microscope adaptor. Pictures of each of the sliced and stained orchid root cross sections were taken. To determine the percent coverage of the 4

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mycorrhizal fungi, the pictures of the cro ss sections where scaled in at 75% on a computer. A 200 x 300 transparent grid was he ld up to the computer screen. One grid was approximately 0.5 cm x 0.5 cm. The number of grids the mycorrhizal fungi appeared on was counted and divided by the total number of grids the entire orchid root cross section took up. Linear regres sions were then used to de termine whether there was any correlation between the percent coverage of fungi and each of the fitness correlates for both orchid species. Furthermore, a t-test was performed to compare the mean percent coverage and standard deviations between the two orchid species. RESULTS There was no correlation between the percent coverage of mycorrhizal fungi and the overall orchid fitness for both specie s of orchids (Table 1, Table 2). No significant difference was found in the m ean percent coverage of fungi between the two species of orchids studied (Fig.1). Two orchids out of the 20 T. memor studied did not have any mycorrhizal fungi. Eight M. chasei out of the 25 specimens studied did not contain any mycorrhizal fungi. The highest percent coverage of T. memor and M. chasei respectively was 23.08% and 26.01% coverage. The mean percent coverage for M. chasei and T. memor were 11.86% SE 1.74 and 11.66% SE 1.94. DISCUSSION It was predicted in this study that the higher the percent c overage of mycorrhizal fungi, the greater the overall fitness of an individual orchid. I found that this prediction was not supported. There is no correlation between percen t coverage and individual fitness levels 5

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of orchids. This lack of st atistically significant findings s uggests that mycorrhizal fungi amount does not have discernable infl uence on adult orchid fitness. The occurrence of mycorrhizal fungi in orchid roots is said to improve access to nutrient resources, such as P, Cu, Zn, ammoni um and organic C (Bayman et al. 2002). It has been estimated that 80% of an orchid s P requirements, and 25% of nitrogen requirements are delivered by fungi (Johnson et al. 1997). If fungi are so essential to nutrient uptake for canopy orchid s, it is conflicting that 10 out of the 45 total orchid specimens studied did not have fungi in their ro ot system. One explana tion to this is that because of the consistent rainfall and high mist content of the Monteverde cloud forests, essential nutrients are obtained from the environment through water sources. A past study proved that adult orchids thrive without the aid of any fungus or other micro-organisms, provided that they ar e supplied with an adequate mineral nutrient solution and a suitable amount of sugar at the proper hydrogen-ion co ncentration (Janos 1983). If planted on an unfavorable medium, su ch as starch, they need the aid of some fungus or other agent that can change the starch to sugar and can maintain proper pH (Janos 1983). All terrestrial orchids have root hairs and all epiphytic orchids produce them under conditions of sufficient moisture (Benzing 1984). Root hairs increase surface area providing more space and greater opportuni ty to optimize nutrient absorption from whatever medium they are growing on. The lack of correlation between percent coverage of fungi and overall fitness suggests that mycorrhizal fungi are generally not as critical for adult plants as for germinating seeds. Seeds of one genus or sp ecies of orchids would germinate only in the presence of the fungus from that particular orchid or others of closely related genera 6

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(Curtis 1939). The amount of fungi, if any, is not crucial to adult orchids productivity and fitness. In a past st udy, it was inferred that endo-my corrhiza may only contribute to plant fitness by dissuading environmental pathogens and parasites from taking over and potentially killing the orchid (Bayman et al 2002). It is not k nown if there are any potentially harmful parasites or pathogens to orchids in Monteverde Cloud Forests. Mycorrhizal fungi also frequently reduce the incidence of soil-borne diseases, such as viruses that are stimulated by improved plan t nutrition, growth a nd other physiological factors (Bayman 2002). It is possible that fungi may not have any impact on adult orchid fitness and productivity. Fungi may benefit from the orch id, but may not provide anything in return for the adult host (Benzing 1984). Mycorrhizae may merely be present as remnants from germination, vestigial symbiont s, and the amount of fungi pr esent may be trivial for an adult orchid. Monteverde is nutrient rich in comparison to drier more temperate forests. It may be that adult orchids have other m eans of obtaining essent ial nutrients through alternative processes, allowing them to shed fungi. This might explain why 10 out of 45 individuals examined lacked hyphae. Mycorrhizae are extremely sensitive to ozone-generated pl ant stress (Gardes 2002). It is strongly sugges ted that there may be ozone generated plant stress in Monteverde at the two altitudes at which the specimens were collected. This leads to another theory concerning the lack of corre lation between percent coverage of fungi and orchid fitness and reasons why 10 of the 45 specimens st udied were found without any fungi. Ultimately the genotypes of the plan ts and fungi involved determine the potential functioning of the symbiosis (Curtis 1939). Ho wever, mycorrhizal absence and lack of 7

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correlation can be related to environmental conditions and ever changing inter-species interactions in the cloud forest s of Monteverde. It has also been proven that mycorrhizal dependency varies greatly among taxa and varieties of plants (Benzing 1995). In order to further study the importan ce of mycorrhizae in adults, a closer examination of exactly what point after germ ination orchids may shed their mycorrhizae without putting productivity and fitness at risk. It is a possibility that mycorrhiae werent actually shed but were at such low densities that were impossible to det ect in this survey. The question at hand for future studies could be that if newly germinated orchids were to shed their fungi prematurely, will they be more prone to environmental parasites? Another question could be if they shed th eir fungi too early, w ill they have not yet developed their root hairs fully and as a resu lt will this inhibit nutrient and water uptake? Despite the fact that these questions are st ill unknown, this study provides evidence that the coverage of mycorrhizae have no affect on epiphytic adult orchid fitness and productivity. ACKNOWLEDGEMENTS I would like to thank Karen Masters for her most excelle nt ability to recognize orchid species. I couldnt have done this project without her direction throughout my entire investigation. I would also like to thank TA Tom for taking his time to help me climb canopy trees and helping me with all my stats. I am thankful for Cams outstanding skill in editing papers and her patience. Last but not least, I would like to express my appreciation to Kat for her marvelous climbing aptitude and dexterity with a sling shot and all our adventures together, they will not be forgotten. 8

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LITERATURE CITED Bayman, P., E.J. Gonzalez, J.J. Fumero, and R.L. Tremblay. 2002. Are Fungi Necessary? How Fungicides Affect Growth and Survival of the Orchid Lepanthes rupestris in the Field. In: The Journal of Ecology. Ackerman J.D. and J.T. Ot ero, eds. British Ecological Soceity, Cambridge, BR, pp. 1002-1008. Benzing, D.H., 1995. Vascular Epiphytes In: Forest Canopies Lowman, M.D. and N.M. Nadkarni, eds. The Academic Press, San Diego, CA, pp. 233. Benzing, D.H., J.T. Atwood, Jr., 1984. Orchidaceae: Ancestral Habitats and Current Status In Forest Canopies In: Systematic Botany Gilmartin, A.J. and W.L. Stern, eds. American Soceity of Plant Taxonomists, New York, NY, pp. 155-165. Curtis, J.T., 1939. The Relation of Specificity of Orch id Mycorrhizal Fungi to the Problem of Symbiosis. American Journal of Botany 26: 390-399. Dressler, R.L., 1990. The Orchids: Natural History and Classification Harvard University Press, Cambridge, MA, pp. 76-79. Gardes, M., 2002. An Orchid-Fungus Marriage: Ph ysical Promiscuity, Conflict and Cheating. New Phytologist 154: 4-7. Hammel, B.E., M.H. Grayum, C. Herrera,, and N. Zamora, 2003. Manuel de Plantas de Costa Rica Volumen III. Missouri Botanical Garden Press, St. Louis, MI, pp. 280 and 544. 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 Mutualism-Parasitism Continuum. New Phytologist 135: 575-586. Perry, D. 1978. A method of access into the crowns of emergent of canopy trees. Biotropica 10: 155-157 Walter, K.S. 1983. Orchidaceae (Orquideas, Orchids) In: Costa Rica Natural History D.H. Janzen, ed. The University of Chicago Press, Chicago, IL, pp. 282-292. Weller, S.Y. 2002. Abundance of vesicular-arbuscular mycorrhizae in adult epiphytic orchidaceae between two canopy substrates. In: UCEAP-IMV: Tropical Biology and Conservation Spring 2002 EAP. The University of California Education Ab road Program and the Monteverde Institute. 9

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FIGURES AND TABLES 0 2 4 6 8 10 12 14 16 Masdevalia chaseiTrichosalpinx memor Orchid SpeciesMean Percent Coverage n = 25 n = 20 Figure 1. The mean percent cove rage of mycorrhizal fungi with standard error on two orchid species: Masdevallia chasei and Trichosalpinx memor. There is no significant difference in the mean percent coverage between the two orchid species. (T-test: t = 0.077, F = 0.0059, PValue = 0.39, df = 1) ________________________________________________________________________ 10

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11 Table 1. The five fitness determinants corre lated with percent coverage of fungi in Masdevallia chasei and the R^2 value, P-Value, the total sample size (n), and the FRatio. FITNESS CORRELATES R^2 P-VALUE n F-Ratio # of Leaves 0.00 0.90 25 0.02 Total # of Leaves 0.00 0.98 25 0 # of Inflorescences 0.17 0.43 25 0.04 Total # of Inflorescences 0.03 0.45 25 0.60 Leaf + Stem Length (cm) 0.00 0.93 25 0 Table 2. The five fitness determinants corre lated with percent coverage of fungi in Trichosalpinx memor and the R^2 value, P-Value, the total sample size (n), and the FRatio. FITNESS CORRELATES R^2 P-VALUE n F-Ratio # of Leaves 0.02 0.59 20 0.32 Total # of Leaves 0.01 0.77 20 0.09 Total # of Inflorescences 0.07 0.25 20 1.40 Length (cm) of Longest Stem 0.00 0.93 20 0.00 Length (cm) of Longest Leaf 0.02 0.64 20 0.23