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Regulation of photosynthetic pigments in tropical understory and gaps

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Title:
Regulation of photosynthetic pigments in tropical understory and gaps
Translated Title:
Regulación de pigmentos fotosintéticos en el sotobosque tropical y en los claros del bosque ( )
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Book
Language:
English
Creator:
Westphal, Maiken
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Subjects / Keywords:
Photosynthetic pigments   ( lcsh )
Understory plants--Costa -Rica--Puntarenas--Monteverde Zone   ( lcsh )
Cloud forest ecology--Costa Rica   ( lcsh )
Pigmentos fotosintéticos
Plantas del sotobosque--Costa Rica--Puntarenas-- Zona de Monteverde
Ecología del bosque nuboso--Costa Rica
Tropical Ecology 2008
Ecología Tropical 2008
Genre:
Reports   ( lcsh )
Reports

Notes

Abstract:
A plant can manipulate its absolute and relative amounts of photosynthetic pigments in different light environments (Hopkins, 1995, Goncalves and Vieira, 2001). Leaf samples from ten gap and ten understory plants were collected from Calyptrogyne brachystachys (Arecaceae), Heliconia monteverdensis (Heliconiaceae), and Piper ariteum (Piperaceae), and their chlorophylls a, b, and carotenoid concentrations were found. The total concentration of chlorophylls a, b, total chlorophyll and carotenoids were significantly higher (p = <0.05) in the understory leaf samples of C. brachystachys and P. auriteum, but higher in the gap samples of H. monteverdensis. Ratios of chlorophyll a to chlorophyll b were significantly greater for gap samples of all three species. A higher concentration of chlorophyll and carotenoids in the understory plants of C. brachystachys and P. auriteum suggests they are adjusting the absolute and relative amounts of pigments to make use of sparse light in the understory. H. monteverdensis utilizes its photosynthetic pigments slightly differently, acting much like a canopy plant.
Abstract:
Una planta puede manipular absolutamente la cantidad relativa de pigmentos fotosintéticos en los diferentes ambientes de luz (Hopkins, 1995, Goncalves y Vieira, 2001). Se colectaron muestras de 10 plantas de Calyptrogyne bracystachys (Arecaceae), Heliconia monteverdensis (Heliconiaceae) y Piper ariteum (Piperaceae), y se midieron las concentraciones de clorofila a y b, y carotenoides en el sotobosque y en los claros del bosque.
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Text in English.
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Born Digital

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usfldc doi - M39-00050
usfldc handle - m39.50
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A plant can manipulate its absolute and relative amounts of photosynthetic pigments in different light environments (Hopkins, 1995, Goncalves and Vieira, 2001). Leaf samples from ten gap and ten understory plants were collected from Calyptrogyne brachystachys (Arecaceae), Heliconia monteverdensis (Heliconiaceae), and Piper ariteum (Piperaceae), and their chlorophylls a, b, and carotenoid concentrations were found. The total concentration of chlorophylls a, b, total chlorophyll and carotenoids were significantly higher (p = <0.05) in the understory leaf samples of C. brachystachys and P. auriteum, but higher in the gap samples of H. monteverdensis. Ratios of chlorophyll a to chlorophyll b were significantly greater for gap samples of all three species. A higher concentration of chlorophyll and carotenoids in the understory plants of C. brachystachys and P. auriteum suggests they are adjusting the absolute and relative amounts of pigments to make use of sparse light in the understory. H. monteverdensis utilizes its photosynthetic pigments slightly differently, acting much like a canopy plant.
Una planta puede manipular absolutamente la cantidad relativa de pigmentos fotosintticos en los diferentes ambientes de luz (Hopkins, 1995, Goncalves y Vieira, 2001). Se colectaron muestras de 10 plantas de Calyptrogyne bracystachys (Arecaceae), Heliconia monteverdensis (Heliconiaceae) y Piper ariteum (Piperaceae), y se midieron las concentraciones de clorofila a y b, y carotenoides en el sotobosque y en los claros del bosque.
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Text in English.
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Photosynthetic pigments
Understory plants--Costa -Rica--Puntarenas--Monteverde Zone
Cloud forest ecology--Costa Rica
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Pigmentos fotosintticos
Plantas del sotobosque--Costa Rica--Puntarenas-- Zona de Monteverde
Ecologa del bosque nuboso--Costa Rica
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Tropical Ecology 2008
Ecologa Tropical 2008
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Reports
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CIEE
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t Monteverde Institute : Tropical Ecology
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Regulation of Photosynthetic Pigments In Tropical Understory and Gaps Maiken Westphal Department of Biochemistry, University of Wisconsin -Madison ABSTRACT A plant can manipulate its absolute and relative am ounts of photosynthetic pigments in different light environments (Hopkins, 1995, Goncalves and Vieira, 2001). Leaf samples from ten gap and ten understory plants were collected from Calyptrogyne brachystachys (Arecaceae) Heliconia monteverdensis (Heliconiaceae) and Piper ariteum (Piperaceae), and their chlorophylls a, b, and caro tenoid concentrations were found. The total concentration of chlorophylls a, b, total chlorophyll and carotenoids were significantly higher (p = <0.05) in the understory leaf samples of C. brachystachys and P. auriteum but higher in the gap samples of H. monteverdensis Ratios of chlorophyll a to chlorophyll b were significantly greater for gap samples of all three species. A hig her concentration of chlorophyll and carotenoids in the understory plants of C. brachystachys and P. auriteum suggests they are adjusting the absolute and relat ive amounts of pigments to make use of sparse light in the understory. H. monteverdensis utilizes its photosynthetic pigments slightly differently, actin g much like a canopy plant. RESUMEN Una planta puede manipular absolutamente la cantida d relative de pigmentos fotosintticos en ambientes con diferente luz (Hopkins, 1995, Goncalves y Vieir a, 2001). Muestras de hojas de 10 plantas en el sotobosque y en claros de bosque fueron colectadas de Calyptrogyne bracystachys (Arecaceae) Heliconia monteverdensis (Heliconiaceae) y Piper ariteum (Piperaceae), y se midieron las concentraciones de clorofila a y b, y carotenoides. La concentracin total de clorofila a, clorofila b y carotenoides fu e significativamente mayor en las muestras del sotobo sque para C. brachystachys y P. auriteum pero mayor en los claros de bosque para H. monteverdensis Proporciones de clorofila a: clorofila b fueron m ayores en las muestras del claro de bosque para las tres espe cies. Una mayor concentracin de clorofila y carotenoides en las plantas del sotobosque C. brachystachys y P. auritum sugieren que estas ajustan la cantidad relativa y absoluta de pigmentos para usa r la luz escasa en el sotobosque. H. monteverdensis utiliza los pigmentos fotosintticos un poco difere nte a las otras dos especies, comportndose ms com o una planta de dosel. INTRODUCTION Tropical understory plants live in an environment t hat has low light, high relative humidity, low wind, and moderate temperature (Runde l and Gibson, 1996). Solar radiation levels in the understory are between 5 an d 10 m mol m-2 s-1 and less than 0.5% of sunlight reaches the forest understory (Pearcy 1983 ). Sunflecks, brief periods of a direct beam of solar radiation, provide between 10-78% of the total photon flux density on the forest floor, having profound changes on the plant’ s photosynthetic process (Chazdon 1986b). Contrastingly tropical understory plants th at grow in light gaps receive between 400-1500 m mol m-2 s-1 of solar radiation (Kursar and Coley, 1999). These two environments with different light allotments may af fect how a plant photosynthesizes.

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Photosynthesis consists of two photosystems (PS), which accept the energy from a photon and use this energy to create adenosine tr iphosphate. Furthermore light harvesting complexes (LHC), in the photosystems, ac t like antennae, using chlorophyll to capture the maximum amount of photons and shuttle t hem to the reaction center. Photosynthetic pigments absorb in the visible light range. The primary and the most abundant pigment for absorbing photons is chlorophy ll a There are also two accessory pigments that aid in light absorption, chlorophyll b and carotenoids (Raven, Evert, and Eichhorn, 1999). Production of all of these pigment s is very costly to the plant, but if an understory plant is to be a viable competitor it mu st be efficient with the light it receives. Carotenoids are present in all photosynthetic organ isms and protect the plant from photooxidation by absorbing and dissociating excess ener gy from chlorophyll. For those plants that end up in a gap they change their photosynthet ic pigments, investing mostly in chlorophyll a and carotenoids. Chlorophyll a will absorb most the light these plants need and the carotenoids may become more important for p rotection from this new environment, having less of a role as a secondary p igment. Each of these photosynthetic pigments maximum absorption is at different wavelen gths, which is how their total concentration can be calculated. This study compares the concentration of chlorophyl l a chlorophyll b and carotenoids between the understory plants Calyptrogyne bracystachys (Aracaceae) Heliconia monteverdensis (Heliconiaceae) and Piper ariteum (Piperaceae). These species were chosen because they are found in the s haded understory and can persist and even excel in light gaps. H. monteverdensis naturally grows in open areas, but once it is established it can persist for many years in the re generating forest (Janzen, 1983). The calculated chlorophyll and carotenoid concentration s give insight as to how these specific species adjust their pigments in different light en vironments. Plants in the light gap receive a higher intensity of light and therefore a re expected to have lower concentrations of chlorophyll a and b Alternatively, carotenoids concentration is harder to predict because they are not needed so much as a secondary pigment in this environment but are necessary to protect the plant from photo-oxidation In addition with less light available in the shaded understory, the plants of this habita t should have higher chlorophyll b concentrations than gap plants. This is because un derstory plants are using their increased chlorophyll b to jump start PSII and the whole photosynthetic pr ocess when in a sunfleck. Carotenoids in this environment could p lay a different role, less protection is needed from photo-oxidation, but more carotenoids c an help photosynthesis by absorbing light in the 470 nm ranges. Thus adapting with diff erent light conditions in the tropical understory, plants should change their relative abu ndance of photosynthetic pigments. MATERIALS AND METHODS Data collection occurred in the Tropical Cloud Fore st of Monteverde, Costa Rica behind the Monteverde Biological Station at approximately 1535 meters in elevation. The methods used for this research follow those used by Wallentine (2006). Ten leaves from each of the study species were collected from the u nderstory and from light gap plants, for a total of 60 samples. Each leaf sample was the n cut into a five by five centimeter square using a cardboard stencil and massed. The pi gments were extracted by adding 7ml of 85% acetone solution at a pH of 6.5 to shredded pieces of the leaf sample in a test

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tube. This solution precipitated for 15 minutes and was shaken every five minutes for 30 seconds to make sure the solution mixed properly. N ext the samples were centrifuged at 4000 rpm, and the total volume of the decanted solu tion containing the pigments was recorded. Next, 2 ml of this decanted solution was added to 8 ml of 85% acetone to dilute the sample. A small portion of this mixture was pou red into a cuvet and the absorbance was measured at 663, 646, and 470 nm. The concentra tions based mass of the leaf of chlorophyll a chlorophyll b and carotenoids was calculated using the followin g equations from Lichtenthaler and Welber (1983): Chlorophyll a (mg/g) = [12.21 (Abs 663 ) – 2.81 (Abs 646 )] x [Purified Volume (ml)] [200] x [Mass of Leaf Used (g)] Chlorophyll b (mg/g) = [20.13 (Abs 646 ) – 5.03 (Abs 663 )] x [Purified Volume (ml)] [200] x [Mass of Leaf Used (g)] Carotenoids (mg/g) = {1000 (Abs 470 ) – 3.27[chl a ] – 104 [chl b ]} x {Purified Volume (ml)} {45400} x {Mass of Leaf Used (g)} Then the ratios of chlorophyll a to chlorophyll b are determined by dividing one from the other. Finally a t-test was performed between the p igment concentrations of the light and dark plants, checking for significance. RESULTS Light quality did in fact change the concentration of the total photosynthetic pigments. The H. monterverdensis gap leaves were collected from very large mature pl ants while the leaves collected for this species from the shad e habitat were relatively smaller. The total chlorophyll concentrations ranged between 0.0 076 mg/g and 0.0586 mg/g. Shaded leaves of C. brachystachys and P. ariteum had a higher amount of chlorophyll, while H. monterverdensis had a higher amount of chlorophyll in the leaves f rom the light gap (Figure 1, C. brachystachys t = 2.364, dof = 18, p = 0.0295, H. monteverdensis t = 11.266, dof = 18, p = <0.0001, P. ariteum t = 2.594, dof = 18, p = 0.0183). Comparing the chlorophyll a concentrations between the species shows similar t rends to the first figure. Chlorophyll a is the main pigment and is in very high concentrati ons in the gap plants of H. monteverdensis while the others have a higher concentration in th e understory plants. (Figure 2, C. brachystachys t = 1.841, dof = 18, p = 0.0822, H. monteverdensis t = -11.889, dof = 18, p = <0.0001, P. ariteum t = 2.395, dof = 18, p = 0.0277). Concentrations of chlorophyll b are much smaller than chlorophyll a with the highest chlorophyll b concentration equaling the lowest concentration of chlorophyll a. This also shows similar trends to the total chlorop hyll concentration graph. Interestingly the C. brachystachys understory and H. monteverdensis gap have almost equal concentrations, with both being the highest concent ration for all samples. (Figure 3, C. brachystachys t = 3.780, dof = 18, p = 0.0015, H. monteverdensis t = -3.754, dof = 18, p = 0.0015, P. ariteum t = 3.228, dof = 18, p = 0.0047). Using data from the two previous graphs a ratio was made between the two chlorophyll concentrations. Differences in the chlorophyll a and b ratios ranged between 2.1541 mg/g and 4.1066 mg/g. The ratio of chlorophyll a to chlorophyll b was higher in the gap environment of all three spe cies. The gap plants have much more chlorophyll a than b making the ratio of the two pigments

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higher for these samples (Figure 4, C. brachystachys t = -8.184, dof = 18, p = <0.0001, H. monteverdensis t = -3.493, dof = 18, p = 0.0026, P. ariteum t = -3.777, dof = 18, p = 0.0014). The next graph shows that shaded understor y leaves in C. brachystachys and P. ariteum had a greater concentration of carotenoids, while the gap plants of H. monteverdensis had a greater concentration. Carotenoid concentrati ons were at a lowest of 0.0039 mg/g and highest of 0.0347. (Figure 5, C. brachystachys t = 4.117, dof = 18, p = 0.0006, H. monteverdensis t = -11.362, dof = 18, p = <0.0001, P. ariteum t = 2.754, dof = 18, p = 0.0131). DISCUSSION A previous study has shown differences in the quali ty and quantity of light cause some species to compensate with the abundance of chlorop hyll and carotenoids in their leaves (Tinoco-Ojanguren and Pearcy, 1995). Wallentine (20 06) found that plants in the understory and canopy use different techniques to c apture light. Since the canopy leaves have a more stable supply of light it is unnecessar y to have such high chlorophyll concentrations. This study found that total chlorop hyll concentrations were higher in shaded leaves for C. brachystachys and P. auriteum, but gap leaves of H. monteverdensis had more chlorophyll. Day (1996) showed that mature leaves have higher chlorophyll concentrations, which could explain why H. monteverdensis have such a high concentration of chlorophyll. In order to completel y capture light from sunflecks, shaded leaves may need to have more chlorophyll. Looking at the ratios between the concentration of chlorophyll a and chlorophyll b indicates the range of light that the plant absorbs Not surprisingly individual chlorophyll a and b concentrations reflect those of the total chloroph yll concentrations. Chlorophyll b is associated with photosystem II (PSII), and the starting point of the whole photosynthetic process (Hopkins, 1995). This study found that the understory plants in the gap had a higher ratio of chlorophyll a to chlorophyll b Using the graphs of the individual chlorophyll pigments shows that the change in the ratio is due to chlorophyll b increasing and not a decrease of chlorophyll b This finding suggests that the shaded understory plants use more chlorophyll b to improve the efficiency of PSII. One important trend to note is that the total carot enoids concentration mirrors that of total chlorophyll concentration. This could mean that as chlorophyll levels increase in the gap plants carotenoids are used to protect agai nst photo-oxidation, but when chlorophyll concentration is higher in the understo ry plants carotenoids are used more as secondary pigments. Perhaps the level of chlorophyl l a is the main factor in determining the role of carotenoids. Plants employ multiple techniques in order to take advantage of the light environment they belong to. Those growing in an und erstory light gap have less variable light than those in the shaded understory, and can take advantage of this by creating more chlorophyll a to capture the light. Shaded plants have to use di fferent strategies to ensure they will have enough light to grow. C. brachystachys and P. ariteum alter their pigments to increase their light capturing ability in the un derstory. One way to do this is to increase the amount of carotenoids and chlorophyll b in the leaves to be used as accessory pigments. However, H. monteverdensis uses different light capturing techniques, often the opposite of the other two plants. In this way H. monteverdensis is acting similarly to a

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nrr canopy species, by biding its time in the understor y and waiting for a gap to reach their full potential. The biochemistry of photosynthesis is still not fully understood and further investigation as to how individual plants function can give insights as to how species, populations, and communities interact. FIGURES FIGURE 1. The total chlorophyll concentration for l eaves of three understory species that also persist in treefall gaps. Total chlorophyll represents the tot al chlorophyll a and b as measure by spectrophotometry. Blue bars represent the mean total chlorophyll conc entration for ten understory individuals, and the p urple show means for individuals in treefall gaps in an o pen canopy. Error bars show the standard deviation. The asterisk shows a significant difference at p < 0.05 (see text). nrr * FIGURE 2. The total chlorophyll a concentration for leaves of three understory speci es that also persist in treefall gaps. Chlorophyll a concentrations were measure by spectrophotometry. Blue bars represent the mean tot al chlorophyll concentration for ten understory individuals, and the purple show means f or individuals in treefall gaps in an open canopy. Error bars show the standard deviation The asterisk shows a significant difference at p < 0.05 (see text).

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FIGURE 4. The ratio of chlorophyll a to b concentration for leaves of three understory specie s that also persist in treefall gaps. Chlorophyll a and b concentrations were measured using spectrophotometry. Blue bars represent the mean tot al chlorophyll concentration for ten understory individuals, and the purple show means f or individuals in treefall gaps in an open canopy. Error bars show the standard deviation. The asterisk shows a significant difference at p < 0.05 (see text). nrr * nrr * FIGURE 3. The total chlorophyll b concentration for leaves of three understory specie s that also persist in treefall gaps. Chlorophyll b concentrations were measured using spectrophotometry. Blue bars represent the mean tot al chlorophyll concentration for ten understory individuals, and the purple show means f or individuals in treefall gaps in an open canopy. Error bars show the standard deviation. The asterisk shows a significant difference at p < 0.05 (see text).

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nrr * FIGURE 5. The total carotenoid concentration for leaves of three understory specie s that also persist in treefall gaps. Carotenoid concentrations were measured using spectrophotometry. Blue bars represent the mean total chlorophyll conc entration for ten understory individuals, and the purple show means for individuals in treefa ll gaps in an open canopy. Error bars show the standard deviation. The asterisk shows a signif icant difference at p < 0.05 (see text). ACKNOWLEDGEMENTS Thank you to Alan Masters for helping me work out t he details of this project and helping me get throu gh rough spots. I would also like to thank Pablo Allen and Moncho Caledrn for getting all of my equipmen t, figuring out my statistics, and answering all my te dious questions. I appreciate Estactin Biologica f or allowing me to do my research on the property. Fina lly thanks to Karen Masters for answering any quest ion that I had. LITERATURE CITED Chazdon, R. L. Fetcher, N. 1984. Photosynthetic lig ht environments in a lowland tropical rain forest in Costa Rica. Journal of Ecology. 72: 553-564. Chazdon, R. L. Pearcy, R. W. 1991. The importance o f sunflecks for forest understory plants. BioScience. 41: pp 760-766. Day, Thomas A. Howells, B.W. Ruhland, C.T. 1996. Ch anges in growth and pigment concentrations with leaf age in pea under modulated UV-B radiation field treatments. Plant Cell & Environment 19: pp. 101-108 Hopkins, W. 1995 Introduction to Plant Physiology John Wiley and Sons, Inc. New York, New York. pp. 125-142, 173-183, 341-360. Janzen, D. H. 1983. Costa Rican Natural History. The University of Chicago Press. Chicago, IL. pp 249-251

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Kursar, T. A. Coley, P. D. 1999. Contrasting modes of light acclimation in two species of the rainforest understory. Oecologia 121: pp 489-498. Raven, P., R. Evert, S. Eichhorn. 1999. Biology of Plants. W.H. Freeman and Company, New York, NY. page 133. Tinoco-Ojanguren, C. Pearcy, R. W. 1995. A comparis on of light quality and quantity effects on the growth and steady-state and dynamic photosynthetic characteristics of three tropical tree species. Functional Ecology. 9: pp 222-230. Wallentine B.D. 2006. Tropical Cloud Forest canopy and subcanopy adapt to different light environments by regulating photosynthentic pi gments. CIEE Fall 2006. Pp. 31-36