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Epiphyllic shading on host plant leaves: photo-acclimation to liverwort and lichen cover

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Title:
Epiphyllic shading on host plant leaves: photo-acclimation to liverwort and lichen cover
Translated Title:
Las epífilas sombrean las hojas de la planta hospedera: Foto-aclimatación a hepáticas y cobertor de líquenes ( )
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Book
Language:
English
Creator:
Addis, Claire
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Subjects / Keywords:
Lichens--Ecology--Costa Rica--Monteverde Biological Station   ( lcsh )
Liverworts--Ecology--Costa Rica--Monteverde Biological Station   ( lcsh )
Plants--Adaptation--Costa Rica   ( lcsh )
Cloud forest ecology--Costa Rica   ( lcsh )
Understory plants--Costa Rica   ( lcsh )
Líquenes--Ecología--Costa Rica--Monteverde--Estación biológica
Hepáticas--Ecología--Costa Rica--Monteverde--Estación biológica
Plantas--Adaptación--Costa Rica
Plantas del sotobosque--Costa Rica
Tropical Ecology 2008
Epiphyllic shading
Calyptrogyne gneisbregntiana
Ecología Tropical 2008
Sombreado de Epífilas
Calyptrogyne gneisbregntiana
Genre:
Reports   ( lcsh )
Reports

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Abstract:
Epiphylls are ubiquitous throughout the Tropics and may significantly shade their host leaves. Anthony et al. (2002) document increased levels of chlorophylls a and b in leaves with significant lichen coverage on two tropical understory plants in Australia, suggesting host leaves may respond to epiphyll shading by increasing photosynthetic pigments. Reaction of plants to the second major group of tropical epiphylls, liverworts, has not been studied. The purpose of this study was to see if a neotropical palm, Calyptrogyne gneisbregntiana, compensates for epiphyll cover by both lichens and liverworts. In addition to chlorophylls a and b, I investigate whether carotenoid levels also increase due to increased epiphyllic shading. The pigments of 80 understory leaf samples with either full lichen or full liverwort cover were extracted in acetone and analyzed using a spectrophotometer. It was found that only shading by lichens resulted in significantly higher chlorophylls a, b and carotenoids (mean = 142.95 ± 0.0350 ug/g, 62.4 ± 0.0178, and 77.5 ± 0.0188, respectively, P< 0.05) and per area for chlorophyll a and carotenoids (mean = 2.6 ± 0.0006 ug/cm2 and 1.45 ± 0.0003, respectively, P< 0.05). Ratios of chlorophyll a: b and total chlorophyll: carotenoids were not different between leaflets with 0% and 100% epiphyllic lichen or liverwort cover. These data show that C. gneisbregntiana compensate for lichen cover but not liverwort cover, and suggest that plants with epiphyllic lichens photo-acclimate to shading by increasing the concentration of light-harvesting pigments. The lack of significant increases in pigments seen in plants with liverwort cover may be due to habitat differences, where the plants may already be compensating to their full extent in response to environmental factors.
Abstract:
Las epífilas se ubican a través de los trópicos y puede de manera significativa sombrear las hojas hospederas. Anthony et al. (2002) documentan un aumento en los niveles de clorofila a y b en las hojas con una cobertura significativa de líquenes en dos plantas tropicales en el sotobosque de Australia, sugiriendo que las hojas hospederas pueden responder a la sombra provocada por las epífilas incrementando los pigmentos fotosintéticos. No se han estudiado la reacción de las plantas para el segundo gran grupo de epífilas tropicales, y hepáticas. El propósito de este estudio fue observar si la palma neotropical Calypterogyne gneisbregntiana, presenta alguna compensación por la cobertura tanto de líquenes como de hepáticas.
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Text in English.
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University of South Florida Library
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University of South Florida
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All applicable rights reserved by the source institution and holding location.
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usfldc doi - M39-00049
usfldc handle - m39.49
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SFS0001225:00001


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Epiphyllic shading on host plant leaves: photo-acclimation to liverwort and lichen cover Claire Addis Department of Biology, Luther College ABSTRACT Epiphylls are ubiquitous throughout the Tropics and may significantly shade their host leaves. Anthony et al (2002) document increased levels of chlorophylls a and b in leaves with significant lichen coverage on two tropical understory plants in Australia, suggesting host lea ves may respond to epiphyll shading by increasing p hotosynthetic pigments. Reaction of plants to the second major gr oup of tropical epiphylls, liverworts, has not been studied. The purpose of this study was to see if a neotropical p alm, Calyptrogyne gneisbregntiana, compensates for epiphyll cover by both lichens and liverworts. In addition to chlorophylls a and b I investigate whether carotenoid levels also increase due to increased epiphyllic shading. The pigments of 80 understory leaf samples with ei ther full lichen or full liverwort cover were extracted in acetone a nd analyzed using a spectrophotometer. It was foun d that only shading by lichens resulted in significantly higher chlorophylls a, b and carotenoids (mean = 142.95 0.0350 ug/g, 62.4 0.0178, and 77.5 0.0188, respectively, P< 0.05) and per area for chlorophyll a and carotenoids (mean = 2.6 0.0006 ug/cm2 and 1.45 0.0003, respectively, P< 0.05). Ratios of chlorophyll a : b and total chlorophyll: carotenoids were not different between leaflets wit h 0% and 100% epiphyllic lichen or liverwort cover. These data show that C. gneisbregntiana compensate for lichen cover but not liverwort cover and suggest that plants with epiphyllic lichens photo-acclimate to shading by in creasing the concentration of light-harvesting pigm ents. The lack of significant increases in pigments seen in plants with liverwort cover may be due to habitat differe nces, where the plants may already be compensating to their full ex tent in response to environmental factors. RESUMEN Epfilos se ubican a travs de los trpicos y puede n significar sombra para sus hospederos. Anthony e t al. (2002) documentan un aumento en los niveles de clorofila a y b en hojas con una cobertura significante en dos plantas tropicales en el sotobosque de Australia, sugiriend o que los hospederos pueden responder a la sombra p rovocada por los epfilos incrementando los pigmentos fotosintt icos. La reaccin de las plantas a el segundo mayo r grupo de los epfilos tropicales las hepticas, no ha sido estud iado. El propsito de est estudio fue observar si la palma neotropical Calypterogyne gneisbregntiana presenta alguna compensacin por la cobertura tan to de lquenes como de hepticas. En adicin a la clorofila a y b, yo investigu si el nivel de carotenoides aumenta tamb in debido a la sombra provocada por los epfilos. Los pigmentos d e 80 hojas del sotobosque con cobertura total tanto de lquenes como de hepticas fueron extrados con acetona y an alizados utilizando un espectrofotmetro. Se encon tr que solamente la sombra provocada por los lquenes resu lta en un aumento en los niveles de clorofila a, b y carotenoides (X = 142.95 0.0350 ug/g, 62.4 0.0178, y 77.5 0.0188, respectivamente, P< 0.05) y por rea para c lorofila a y carotenoides (X = 2.6 0.0006 ug/cm2 y 1.45 0.0003, respectivamente, P< 0.05). Las p roporciones de clorofila a:b y clorofila total:carotenoides no mostraron dif erencias entre las hojas con 0% y 100% de cobertura por lquenes o hepticas. Estos datos sugieren que C. gneisbregntiana compensa para lquenes pero no para hepticas, y s ugiere que plantas con cubiertas con lquenes se foto-acli matan a la sombra incrementando la concentracin de pigmentos. La falta de un aumento significativo en las plantas cubiertas por hepticas puede deberse a la diferen cia de hbitat, en donde las plantas pueden compensar en plena medi da en respuesta a factores ambientales.

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INTRODUCTION Epiphylls are small photosynthetic epiphytes that t ypically colonize the upper surface of leaves (Richards 1954, in Coley et al. 1993, Bentley 1987, Santessen 1988, in Anthony et al. 2002). They thrive in areas of high rainfall and evaporati on (Richards 1964, in Bentley 1987) and are thus quite common in tropical ecosystems. Epiphyll s reach their highest diversity and abundance in the Tropics, though most epiphyllic communities are dominated by liverworts from the family Lejeuneaceae and lichens. Mosses, algae and cyanob acteria also occur as epiphylls, though with lower frequency (Bentley 1987). The cover of lichens and liverworts on leaves in we t tropical forests can be substantial, in some cases completely covering the leaf (Richards 1 994, in Anthony et al 2002). It has been documented that significant liverwort cover of the leaf reduces the amount of light reaching the leaf by 55-85% (Coley et al 1993). Such shading on the photosynthetic surface of the leaf may reduce the photosynthetic output of the underlying leaf. With only 0.5-5% of light reaching the understory (Chazdon and Fletcher 1984), Coley et al (1993) calculated a possible 20% reduction of photosynthesis. While several studies suggest that shading by epip hylls can reduce photosynthesis (SandJensen 1977, in Coley et al 1993, Roskoski 1981), a more recent study has foun d that leaves of two understory plants photo-acclimate to shading by epiphyllic lichens (Anthony et al. 2002). Leaves colonized by lichens actually had a greater concentration of chlorophylls than did uncolonized leaves, though the rate of photosynthes is was saturated at lower irradiances. This indicates that colonized leaves reached their photo synthetic capacity at lower light levels due to increased shading, which indicates the increase in chlorophylls may be adaptive. Colonized leaves showed a 10-20% higher concentration of chlo rophylls than uncolonized leaves, a difference similar to that of shade tolerant plants compared to canopy leaves. Chlorophylls primarily harvest light energy to be used in photosynthesis (Hopkins 1995). Chlorophyll a is the most abundant pigment and is responsible fo r the transformation of light energy into useable chemical energy. Chlorophyll b is less abundant than chlorophyll a but absorbs light at a different wavelength (approx. 64 6 nm as opposed to chlorophyll a which absorbs best at approx. 663 nm) and thus helps to a mplify the amount of light absorption (Hopkins 1995). The ratio of chlorophyll a:b is thus an indicator of the range of light absorbe d by the plant. Shade environments, are typically ch aracterized by a higher concentration of chlorophyll b due to an increased size of the light-harvesting c omplex. This helps to maximize light absorption in an environment where light is l ess abundant (Smith et al. 1990). Thus the ratio of chlorophylls a:b is likely to decrease moving from sun to shade env ironments, shown by Wallentine (2006). Carotenoids are a less common p hotosynthetic pigment that absorb light at 470 nm. The light energy absorbed by carotenoids i s rapidly transferred to the chlorophylls, so carotenoids are termed accessory pigments. Caroten oids also aid in photo-inhibition. In high light environments, the large amount of energy abso rbed by chlorophyll can damage the cell if the energy is not stored or transferred through pho tochemistry. Carotenoids are able to accept excess light energy as well, thus exerting a photoinhibitive action (Taiz and Zeiger 1991). Accordingly, the ratio of total chlorophylls to car otenoids is an indicator of plant response to high light intensities. In shade environments wher e light is less abundant, it is unlikely that carotenoids are needed for their photo-inhibition p roperties and may instead be used primarily

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for light absorption (Wallentine 2006). For this r eason, the ratio of total chlorophylls to carotenoids is expected to be higher in high light environments and decrease in shade environments, as carotenoids become more essential to aid in light capture. The goals of this study were threefold: first, to see if Calypterogyne gniesbregntiana a neotropical understory palm with lichen epiphylls w ill increase its chlorophyll content, indicating photo-acclimation or compensation by the plant. Se cond, to investigate if liverworts instigate the same photo-acclimation response in plants as lichen s have been shown to demonstrate (Anthony et al. 2002). Finally, to test the levels of carot enoids between leaves with significant epiphyll coverage (liverwort and lichen) to see if carotenoi d concentration is affected in the same manner as chlorophylls a and b It is predicted that epiphyllic coverage by both lichens and liverworts will result in increased levels of all three pigmen ts, based on the idea that more shaded leaves will need to maximize light capture. In addition, i t is predicted that lichens and liverworts will have similar effects on their host plant leaves bec ause both have been shown to substantially cover the surface of leaves. Both have also been d ocumented to significantly reduce the amount of light that reaches the leaf (Coley et al.1993, A nthony et al. 2002), which will likely induce similar responses from host plants. METHODS Study sites and organism Calyptrogyne gniesbregntiana (Arecaceae) is a common understory palm in the lower montane wet and rain forests at Monteverde, Costa Rica and is host to a wide variety of epiphyllous lichens and liverworts (Daniels 1998). This study was conducted in the forest behind the Estacin Biologica at Monteverde. Leaflet samples were collected from two separate populations of C. gniesbregntiana, one along the continental divide at approximately 1 800 m whose epiphyll population was dominated by liverwor ts and the other in the forest near the Estacin at approximately 1500 m dominated by liche ns. Leaf sample collection Leaflet samples with lichens were taken from the lo wer elevation site and leaflet samples with liverwort colonies were taken from the continental divide. Forty leaflet samples were taken from each site; 20 samples with no epiphylls and 20 samp les with 100% epiphyll cover. For a leaflet to qualify as having a100% epiphyll coverage there had to be at least some epiphyll cover on every square cm of the leaflet surface. Samples we re taken from plants with similar canopy cover, approximately 75% shaded, which is the most common condition in the forest studied. Leaflets were consistently taken from the middle ra nge of fronds, usually the frond 2nd or 3rd from the top, uppermost frond. This ensured that s amples were of similar ages, since the youngest leaflets are on the uppermost frond, while the oldest leaflets are found on the lowermost fronds. Leaflets were taken back to the lab at the Estacin Biologica for immediate chlorophyll analysis, thus it was not necessary to store the leaflet samples.

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Pigment analysis The chlorophyll content of the leaflet samples was measured using the following procedure from Wallentine (2006), with slight modification. Leafl ets from each individual plant were measured and cut to an area 25 cm2 using a cardboard stencil and a single edged razor blade. The square section of leaf was then gently scraped using a met al spatula and brushed clean with a stiffbristled paintbrush to remove all epiphylls from th e surface of the leaf. This process did not remove the epidermis of the leaf or damage it in an y way. The 25 cm2 of leaf was then cut into very fine leaf fragments first by slicing the leaf lengthwise into thin strips, then by cutting the strips widthwise into small bits. The mass of the 25 cm2, now in fine leaf fragments, was recorded in grams using a Fischer Scientific T top loading balance. Photosynthetic pigments were extracted from the leaf fragments by adding th e fragments to 7 ml of 85% acetone solution in a test tube. The photosynthetic pigments were a llowed to precipitate in acetone for 15 minutes. During this 15 minute period, the solution s were gently swirled for 30 seconds every 5 minutes in order to facilitate the mixing of the le af fragments with the acetone. The mixture was centrifuged at 4000 rpm with a Premiere XC-1000 cen trifuge to separate the leaf cells and fragments from the acetone-pigment solution. The p urified acetone-pigment solution was then decanted into a graduated cylinder and the volume w as measured in milliliters. Two ml of the acetone-pigment solution were added to 8 ml of 85% acetone in a cuvet. Absorption readings were taken of the diluted acetone-pigment solution at wavelengths of 663, 646, and 470 nm using a Sequoia-Turner Model 340 spectrophotometer. The concentrations of pigments per mass and per area were determined using the following em pirically derived equations (Lichtenthaler and Welbur 1983, in Wallentine 2006): Chlorophyll a (mg/g) = [12.21 (Abs 663 ) – 2.81 (Abs 646 )] x [Purified Volume (ml)] [200] x [Mass of Leaf Used (g)] Chlorophyll a (mg/cm) = [12.21 (Abs 663 ) – 2.81 (Abs 646 )] x [Purified Volume (ml)] [200] x [Area of Leaf Used (cm)] Chlorophyll b (mg/g) = [20.13 (Abs 646 ) – 5.03 (Abs 663 )] x [Purified Volume (ml)] [200] x [Mass of Leaf Used (g)] Chlorophyll b (mg/cm) = [20.13 (Abs 646 ) – 5.03 (Abs 663 )] x [Purified Volume (ml)] [200] x [Area of Leaf Used (cm)] Carotenoids (mg/g) = {1000 (Abs 470 ) – 3.27[chl a ] – 104 [chl b ]} x {Purified Volume (ml)} {45400} x {Mass of Leaf Used (g)} Carotenoids (mg/cm) = {1000 (Abs 470 ) – 3.27[chl a ] – 104 [chl b ]} x {Purified Volume (ml)} {45400} x {Area of Leaf Used (cm)}

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Pigment concentrations were then converted from mg/ g and mg/cm2 to g/g and g/cm2 for the purpose of comparison to literature values. The di fference in pigment concentration between leaves with and without epiphyll coverage was teste d using a two-tailed t-test for the following: chlorophyll a (per mass and area), chlorophyll b (p er mass and area), carotenoids (per mass and area), total chlorophyll concentration (chlorophyll a + chlorophyll b) (per mass and area), the ratio of chlorophyll a to chlorophyll b (per mass a nd area), and the ratio of total chlorophyll to carotenoids (per mass and area). RESULTS In total, 80 leaftlet samples were collected: 40 fr om the continental divide population of C. ghiesbregntiana (liverworts) and 40 from the lower population (lichens). Mean ch lorophyll a (per mass and area) and b (per mass)content and thus total mean chlorophyl l content, as well as mean carotenoid content were higher in leaflets wit h 100% lichen coverage than with no coverage at all (t-test, Table 1, Fig 1, Fig 2). T he concentration of chlorophyll b per area was not different between leaves with and without lichen co ver, but it is worth noting that the p-value was 0.06, which is very close to significant. The trend follows a similar direction, if not quite significant. No difference was observed in mean pi gment content for leaflets with and without liverwort coverage. However, trends are consistent for each pigment (chlorophylls a,b and carotenoids) and show slight increases from leaflet s with no cover and those with 100% liverwort cover. Though not significant, these tre nds point in a direction that leaves are slightly increasing the concentration of photosynthetic pigm ents when shaded by epiphylls. For leaflets with and without lichen or liverwort coverage, ther e was no difference in the ratio of mean chlorophyll a to mean chlorophyll b or the ratio of mean total chlorophyll to mean car otenoid content (Table 1). For all pigments in leaves with 0% epiphyll cover, those from the upper population where the liverworts dominate had higher concentrations t han those collected at the lower population, where lichens dominate (Table 1). However, in leav es with 100% lichen and liverwort cover, concentration values were nearly identical for chlo rophyll a and were lower for both chlorophyll b and carotenoids for leaves with 100% liverwort cove r (Table 1). Nevertheless, chlorophyll a was much higher in concentration for plants with or without epiphyll coverage than either chlorophyll b or carotenoids (Table 1). Leaflet samples taken from the lower population whe re lichens were the dominant epiphyll were greater in mass than those collected from the continental divide where liverworts were the dominant epiphyll (mean = 0.450 0.0553, 0.405 0.0552, respectively; t = -3.692 P < 0.05). For this reason, pigment content was also calculated per area in addition to per mass. In all cases, except for chlorophyll b significant differences detected per mass were al so detected per area (Table 1).

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Table 1 Photosynthetic pigment content ( a b and carotenoids) as well as the ratios of chloroph yll a : b and total chlorophyll: carotenoids. Values in the first two columns are expressed as means SD for leaves with 0% epiphyll cover and 100% epiphyll cov er. The last two columns show the tvalue and corresponding P-value. No difference was observed in pigment content for leaves with and without liverwort colonization. Pigment content was signif icantly different for leaves with and without liche n colonization, except chlorophyll b (g/cm2). Comparisons between the ratios of chlorophyll a:b and total chlorophyll:carotenoids showed no significant diffe rence. 0% Cover 100% Cover T P Liverwort Chlorophyll a (g/g) 138.100 0.0440 145.500 0.0586 0.451 0.6545 Chloro phyll a (g/cm 2 ) 2.250 0.0010 2.300 0.0011 0.158 0.8751 Chlorophyll b (g/g) 53.106 0.0160 55.900 0.021 0.475 0.6373 Chlorophyll b (g/cm 2 ) 1.000 0.0000 0.950 0.0003 0.370 0.7136 Carotenoid (g/g) 65.900 0.0160 68.350 0.0207 0.416 0.6 796 Carotenoid (g/cm 2 ) 1.100 0.0000 1.200 0.0004 0.872 0.3888 Total Chlorophyll (g/g) 191.100 0.0590 201.500 0.0786 0.472 0.6396 Total Chlorophyll (g/cm 2 ) 3.050 0.0009 3.300 0.0015 0.604 0.5496 Chlorophyll a:b (g/g) 2.589 0.2170 2.6 08 0.2785 0.238 0.8142 Chlorophyll a:b (g/cm 2 ) 2.5897 0.2172 2.6085 0.2785 0.238 0.8132 Total Chlor:Car (g/g) 2.870 0.2785 2.892 0.4130 0.184 0.8548 Total Chlor:Car (g/cm 2 ) 2.785 0.3103 2.8078 0.3938 0.196 0.845 Lichen Chlorophyl l a (g/g) 110.0 0.0300 142.95 0.0350 3.173 0.003 Chlorophyll a (g/cm 2 ) 1.9 0.0010 2.6 0.0006 3.164 0.0031 Chlorophyll b (g/g) 42.2 0.0236 62.4 0.0178 3.069 0.004 Chlorophyll b (g/cm 2 ) 0.850 0.000 1.1 0.0003 1.934 0.0606 Caroteno id (g/g) 61.1 0.0180 77.5 0.0188 2.834 0.0073 Carotenoid (g/cm 2 ) 1.1 0.0000 1.45 0.0003 2.626 0.0124 Total Chlorophyll (g/g) 152.2 0.0380 205.4 0.0526 3.651 0.0008 Total Chlorophyll (g/cm 2 ) 2.650 0.0006 3.750 0.0009 4.181 0.0002 Chlorophyll a:b (g/g) 1.944 1.8360 2.313 0.1658 0.895 0.3765 Chlorophyll a:b (g/cm 2 ) 1.944 1.8357 2.313 0.1658 0.895 0.3765 Total Chlor:Car (g/g) 2.560 0.546 2.660 0.2677 0.735 0.4669 Total Chlor:Car (g/cm 2 ) 2.505 0.5623 2.592 0.25 45 0.630 0.5323

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Figure 1. Total chlorophyll (chlorophyll a + chlorophyll b ) content (g/g) found in leaves with 0-100% liverwort (blue) and lichen (pink) coverage. The b ars represent mean values SD. Only the differenc e between leaves with and without lichen coverage was significant (Table 1). Indicates significant difference detected. Figure 2. Carotenoid content (g/g) found in leaves with 0-10 0% liverwort (blue) and lichen (pink) coverage. The bars represent mean values SD. On ly the difference between leaves with and without lichen coverage was significant (Table 1). Indicates significant difference detected. DISCUSSION The goals of this study were to investigate possibl e changes in photosynthetic pigment concentration in leaves with 0% epiphyll coverage a nd 100% epiphyll coverage. Two types of epiphylls were used in this study: liverworts and l ichens. Because lichens shade leaves and photosynthesis is thus saturated at lower light irr adiances (Anthony et al. 2002), plants may

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compensate for this shading by increasing the conte nt of the light harvesting pigments, like chlorophylls a b and carotenoids (Anthony et al. 2002). Here, I find that leaflets with 100% lichen coverage had increased levels of chlorophyll s a and b and carotenoids (Table 1, Fig. 1, Fig 2). The increased level of carotenoids found in l ichen-covered leaves suggests that carotenoids are used for light absorption rather than photo-i nhibition. It is quite probable that light levels were low enough in the understory that the plants s imply had no need for photo-inhibition. Liverworts, on the other, hand did not did not have the same effect on their host leaves. No difference in chlorophyll concentration or carot enoidswas observed between colonized and uncolonized leaves (Table 1, Fig. 1, Fig.2), though trends showing increases in pigments in leaves with liverwort cover suggest slight compensa tion by the leaf. Although it seemed likely that liverworts would generate significant shading and produce similar results to those found with lichens, there may exist possible explanations The leafy, 3-dimensional morphology of most liverworts is very different than that of lich ens, which are mostly flat and strongly adhered to the surface of the leaf. The more open structur e of liverworts may have resulted in less shading, thereby not inducing a photo-acclimation r esponse in the plant and thus not resulting in a significant change in photosynthetic pigment cont ent. An alternative hypothesis is that perhaps there was no observable compensation between leaves with 0% and100% liverwort coverage because climatic variables were such that the plant s were already compensating for lower light conditions. The elevated levels of chlorophylls a, b and caratenoids in plants with 0% cover support this conclusion. The samples with liverwo rt coverage came from the upper population where there may have been increased cloud cover or some other light-limiting characteristic, resulting in increased levels of photosynthetic pig ments, regardless of epiphyll cover. Additionally, leaves from the lower population domi nated by lichens were significantly greater in mass than those from the upper population domina ted byliverworts. This may explain why differences in pigment concentrations were seen wit h increased lichen cover. A thicker leaf may contain more pigments, possibly resulting in a grea ter observed difference in pigment concentration between colonized and uncolonized lea ves than would be seen in the thinner leaves from the higher population. No difference was seen in either of the ratios test ed between colonized and uncolonized leaflets by either lichens or liverworts (Table 1, Fig.2). The ratio of chlorophyll a : b is a good indicator of the range of light absorbed by the pla nt. Since there was no change between leaflets with 0% and 100% coverage, it can be assumed that t here was no difference in the ranges of light absorbed between the two leaflets with different co verage. A reduced chlorophyll a:b ratio is also indicative of shade acclimation. In shaded en vironments, the concentration of chlorophyll b tends to be higher due to the higher proportion of light harvesting complex II (where chlorophyll b is found) which helps to intercept more light and i ncrease the activity of photosystem II (Hopkins 1995, Thomas 1997). Since this reduction was not observed, it can be concluded the amount of shading produced by either the lichens or the liverworts was not enough to invoke such a change in the concentration of chlorophyll b in relation to chlorophyll a as would normally be observed between full sun and shade env ironments. Typically, chlorophyll a:b ratios are greater than one (x = 1.63 0.57 in Wal lentine 2006) for sun plants because canopy plants use main ly chlorophyll a for photosynthesis and do not rely as heavily on other pigments (Wallentine 2 006). Subcanopy plants often have an a:b ratio closer to one because plants use roughly equa l amounts of both pigments in order to maximze the range of light absorption. These data show chlorophyll a:b ratios higher than one

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for leaves with and without epiphyll cover (Table 1 ), as do reported values in Anthony et al. (2002) for understory plants. It is possible that these described differences were not observed because the amount of shading produced by either th e lichens or the liverworts was not enough to invoke such a change in the concentration of chl orophyll b in relation to chlorophyll a as would typically be observed between full sun and sh ade environments. The plants used in this study were found in the understory and therefore al ready living with low light levels. There may not have been much possibility for futher compensat ion, particularily in the upper population of C. gniesbregntiana where uncolonized leaves showed elevated pigment le vels. In addition, the ratio may not have changed because both chlorophyll s a and b increased with increased cover (though the difference was only significant with li chen cover), and chlorophyll a was consistently more abundant, while chlorophyll b was only a small component of the total chlorophyll content. The ratio of total chlorophyll: carotenoids is an i ndicator of the plants’ response to light intensity. In high light environments, a reduced c hlorophyll to carotenoid ratio is common and indicates the degradation of chlorophyll a and/or t he synthesis of carotenoids, which are needed for their photo-inhibitive properties (Taiz & Zeige r 1991, Maxwell 1994, Hopkins 1995). It is reasonable to assume that in shaded environments th is ratio would be increased, due to the lack of a need for photo-inhibition, thus leading to red uced levels of caroteniods. However, this study found no difference between leaves with 0% and 100% epiphyll coverage, which does not support this assumption (Table 1, Fig. 2). Once ag ain, this may have been because the difference in light intensity produced soley by the epiphylls was not great enough to show any difference in the ratio of chlorophyll :carotenoids. Also, beca use all plants involved in this study were understory plants and therefore already shaded, add itional shade provided by epiphyllys is not likley to show a difference like would be found in full sun vs. understory environments. Another more probable explaination is that in this somewhat shaded environment, carotenoids were needed to aid in light absorption rather than photo -inhibition, thus accounting for the lack of relationship between total chlorophyll and caroteno ids that can be explained by photoinhibition. The total chlorophyll is increasing as is the carot enoid content, thus the ratio stays relatively constant between uncolonized and colonized leaves. In conclusion, only plants with significant lichen cover compensated for shading by increasing the concentration of light-harvesting pi gments in their leaves. This provides evidence for a photo-acclimation response in plants to aid i n adaptation to increased shading. What remains unstudied, however, is how much shading pro duced by epiphylls a plant will tolerate before it begins to invest in increased levels of p hotosynthetic pigments. Further studies examining the concentration of pigments along a gra dient of epiphyll coverage, rather than just 0% and 100% cover, may help answer this question. In addition, it may be beneficial to investigate the effect of epiphyllic shading by liv erworts and lichens across environments with varying light levels to see if trends found by this study and others hold true for different environmental conditions. ACKNOWLEDGMENTS I would like extend thanks to all those who assiste d in this study. Thank you to Dr. Alan Masters for invaluable guidance and advice throughout this study. Thank y ou to Pablo Allen Monge and Moncho Calderon for ass istance with statistical analysis and for willingly answeri ng my unending questions. Lastly, I would like to thank the

PAGE 10

Estacin Biologica at Monteverde for allowing me to collect samples in the surrounding forest and CIEE for providing me with this opportunity. LITERATURE CITED Anthony, P. A., J.A.M. Holtum, & B. R. Jackes. 200 2. Shade acclimation of rainforest leaves to colon ization by lichens. Functional Ecology 16: 808-816. Bentley, B.L. 1987. Nitrogen fixation by epiphylls in a tropical rain forest. Annals of the Missouri Botanical Garden 74: 234-241. Chazdon, R. L., and N. Fetcher. 1984. Photosyntheti c light environments in a lowland tropical rain for est in Costa Rica. Journal of Ecology 72:553-564. Coley, P.D., T.A. Kursar, & J. Machado. 1993. Col onization of tropical rain forest leaves by epiphyl ls: effects of site and host plant leaf lifetime. Ecology 74: 619-623. Daniels, J.D. 1998. Establishment and succession of epiphyllic bryophyte assemblages on the fronds o f the neotropical understory palm Geonoma seleri. PhD dissertation, University of North Dakota. 114 pp. Hopkins, W. 1995. Introduction to Plant Physiology John Wiley and Sons, Inc. New York, New York. pp. 125-183, 341-361. Lichtenthaler, H. and A. Wellburn. 1983. Determinat ions of total carotenoids and chlorophylls a and b of leaf extracts in different solvents. Biochemistry Society Transactions 11: 591-592. Maxwell, H.G. & A.J. Young. 1994. Photosynthetic ac climation to light regime and water stress by the C3CAM epiphyt guzmania monostachia: ga s-exchange characteristics, photochemical efficiency and the xanthophylls cycle. Functional Ecology 8: 746-754. Richards, P. W. 1954. Notes on the bryophyte commun ities of lowland tropical rainforest with specific reference to Moraballi Creek, British Guiana. Vegetation 5-6:319-328. Roskoski, J.P. 1981. Epiphyll dynamics of a tropica l understory. Oikos 37:252-256. 1964. The tropical rain forest, an ecological stu dy Cambridge University Press, London 1984. The ecology of tropical forest bryo phytes. New Manual of Bryology Vol.2 (ed. R.M. Schuster): pp. 1233-1270. Nichinan, Miyazaki, Japan. Sand-Jensen, K. 1977. Effect of epiphytes on eelgra ss photosynthesis. Aquatic Botany 3:55-63. Santesson, R. & L. Tibell. 1988. Foliicolous lich ens from Australia. Austrobaileya 2: 529-545. Smith, B., P. Morrissey, J. Guenther, J. Nemson, M. Harrison, J. Allen, and A. Melis. 1990. Response o f the photosynthetic apparatus in Dunaliella salina (green algae) to irradiance stress. Plant Physiology 93: 1433-1440.Taiz, L. and E. Zeiger. 1991. Plant Physi ology The Benjamin/Cummings Publishing Company, Inc. Redwood City, California. pp. 179-216. Thomas, H. 1997. Tansley review no. 92 chlorophyll: a synton and regulator of plastid development. New Phytologist 136: 163-181.

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Wallentine, B.D. 1996. Tropical cloud forest cano py and subcanopy adapt to different light environme nts by regulating photosynthetic pigments. CIEE Student Paper : Fall 2006.


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Epiphylls are ubiquitous throughout the Tropics and may significantly shade their host leaves. Anthony et al. (2002) document increased levels of chlorophylls a and b in leaves with significant lichen coverage on two tropical understory plants in Australia, suggesting host leaves may respond to epiphyll shading by increasing photosynthetic pigments. Reaction of plants to the second major group of tropical epiphylls, liverworts, has not been studied. The purpose of this study was to see if a neotropical palm, Calyptrogyne gneisbregntiana, compensates for epiphyll cover by both lichens and liverworts. In addition to chlorophylls a and b, I investigate whether carotenoid levels also increase due to increased epiphyllic shading. The pigments of 80 understory leaf samples with either full lichen or full liverwort cover were extracted in acetone and analyzed using a spectrophotometer. It was found that only shading by lichens resulted in significantly higher chlorophylls a, b and carotenoids (mean = 142.95 0.0350 ug/g, 62.4 0.0178, and 77.5 0.0188, respectively, P< 0.05) and per area for chlorophyll a and carotenoids (mean = 2.6 0.0006 ug/cm2 and 1.45 0.0003, respectively, P< 0.05). Ratios of chlorophyll a: b and total chlorophyll: carotenoids were not different between leaflets with 0% and 100% epiphyllic lichen or liverwort cover. These data show that C. gneisbregntiana compensate for lichen cover but not liverwort cover, and suggest that plants with epiphyllic lichens photo-acclimate to shading by increasing the concentration of light-harvesting pigments. The lack of significant increases in pigments seen in plants with liverwort cover may be due to habitat differences, where the plants may already be compensating to their full extent in response to environmental factors.
Las epfilas se ubican a travs de los trpicos y puede de manera significativa sombrear las hojas hospederas. Anthony et al. (2002) documentan un aumento en los niveles de clorofila a y b en las hojas con una cobertura significativa de lquenes en dos plantas tropicales en el sotobosque de Australia, sugiriendo que las hojas hospederas pueden responder a la sombra provocada por las epfilas incrementando los pigmentos fotosintticos. No se han estudiado la reaccin de las plantas para el segundo gran grupo de epfilas tropicales, y hepticas. El propsito de este estudio fue observar si la palma neotropical Calypterogyne gneisbregntiana, presenta alguna compensacin por la cobertura tanto de lquenes como de hepticas.
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Text in English.
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Lichens--Ecology--Costa Rica--Monteverde Biological Station
Liverworts--Ecology--Costa Rica--Monteverde Biological Station
Plants--Adaptation--Costa Rica
Cloud forest ecology--Costa Rica
Understory plants--Costa Rica
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Lquenes--Ecologa--Costa Rica--Monteverde--Estacin biolgica
Hepticas--Ecologa--Costa Rica--Monteverde--Estacin biolgica
Plantas--Adaptacin--Costa Rica
Plantas del sotobosque--Costa Rica
653
Tropical Ecology 2008
Epiphyllic shading
Calyptrogyne gneisbregntiana
Ecologa Tropical 2008
Sombreado de Epfilas
Calyptrogyne gneisbregntiana
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CIEE
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