Interpreting Botanical Progress April-June 1998 Cecropia schereberiana in the Luquillo Mountains of Puerto Rico Nicholas V.L. Brokaw......................................91 CAM Photosynthesis in Submerged Aquatic Plants Jon E. Keeley.............................................121 Are Biotic Factors Significant in Influencing the Distribution of Halophytes in Saline Habitats Irwin A. Ungar............................................176 Instructions to ContributorsCECROPIA SCHREBERIANA IN THE LUQUILLO MOUNTAINS OF PUERTO RICO Nicholas V. L. Brokaw Manomet Center for Conservation Sciences P.O. Box 1770 Manomet, Massachusetts 02345 U.S.A. I. Abstract/Resumen II. Introduction A. The Luquillo Mountains III. Biology of Cecropia schreberiana A. The Genus Cecropia B. Description of Cecropia schreberiana Miq. C. Distribution in the Luquillo Mountains D. Flowering, Fruiting, and Seed Production E. Dispersal F. Soil Seed Bank G. Germination H. Growth and Metabolism 1. Seedlings 2. Saplings/Poles 3. Mature Trees I. Mortality and Longevity IV. Dynamics of Cecropia schreberiana A. Human Disturbances B. Landslides C. Background Treefalls D. Hurricanes E. Summary of Cecropia schreberiana Population Dynamics V. Importance of Cecropia schreberiana VI. Conclusion VII. Acknowledgments VIII. Literature Cited IX. Figure legends I. Abstract Cecropia schreberiana Miq. (Cecropiaceae) is a common tree in the Luquillo Mountains of Puerto Rico because it is a pioneer that establishes abundantly after recurrent hurricanes that damage Luquillo forests. In these forests C. schreberiana typically reaches about 20 m in height and 60 cm dbh and has few branches, these bearing large, deeply lobed leaves. The wood is light and weak. Unlike most of its congeners C. schreberiana in Puerto Rico does not have symbiotic ants. It is dioecious and produces wind-pollinated flowers in spikes and abundant minute seeds broadly dispersed by birds and bats. Forest soils contain a high density of its seeds, which lie dormant until canopy opening stimulates germination. With adequate nutrients C. schreberiana grows fast in high light, while non-dominant individuals suffer heavy mortality. It is thought to live 30 to 50 years. Cecropia schreberiana is uncommon in abandoned pastures in the Luquillo Mountains. It colonizes road cuts, landslides, and infrequent, large treefall gaps. Yet these disturbances provide only a limited "background regeneration", which is not sufficient to maintain the species' observed high abundance in Luquillo forests. However, there is widespread and abundant C. schreberiana regeneration after hurricane damage opens the forest canopy. Despite high mortality among these post-hurricane colonizers, enough survive and grow so that C. schreberiana is generally among the ten most common canopy trees in the widespread "tabonuco" forest type. Post-hurricane colonizers mature, senesce, and decline in number, but C. schreberiana remains abundant as seeds in the soil ready to form tree cohorts after disturbance. The status of the C. schreberiana population indicates the developmental status of the forest as a whole. Moreover, C. schreberiana performs a key function in the reorganization of Luquillo forest ecosystems after disturbance, when its abundant regeneration and rapid growth capture and store nutrients. Also, its colonizing saplings may facilitate succession to mature forest by excluding grasses, herbs, and vines that hinder forest development. The biology of this species both reflects and helps drive the dynamics of forests in the Luquillo Mountains. Click Here to Go to Back to Top
RH: AQUATIC CAM PHOTOSYNTHESIS CAM Photosynthesis in Submerged Aquatic Plants Jon E. Keeley Division of Environmental Biology National Science Foundation Arlington, VA 22230 I. Abstract/Resumen II. Introduction III. Diel Acid Changes (?H+) in Submerged Aquatic Plants IV. Criteria for CAM Photosynthesis V. Evidence of the CAM Pathway in Aquatic Plants A. Dark Fixation B. Daytime Deacidification C. CAM Enzymes D. Gas Exchange VI. Other Attributes of Aquatic CAM Plants A. Structural Characteristics 1. Morphological Variation in Isoëtes 2. Other Aquatic CAM Plants B. Inorganic Carbon Source C. Isotope Fractionation VII. Habitat Distribution A. Seasonal Pools B. Lacustrine C. Other Habitats VIII. CAM and the Carbon Budget A. Seasonal Pool CAM Plants B. Lacustrine CAM Plants 1. Sediment CO2 Uptake 2. Factors Affecting Acidification and Deacidification Patterns 3. Contribution of CAM C. Productivity IX. Aquatic CAM Plants in an Aerial Environment X. Diel Acid Changes in Other Aquatic Species XI. Systematic Distribution XII. Evolution of Aquatic CAM Plants A. Patterns of Radiation in Isoëtes 1. Putative Amphibious to Terrestrial Transitions 2. Putative Amphibious to Lacustrine to Terrestrial Transitions B. Patterns of Radiation in Crassula XIII. Conclusions and Areas for Future Research XIV. Acknowledgments XV. Literature Cited I. Abstract Crassulacean acid metabolism (CAM) is a CO2 concentrating mechanism selected in response to aridity in terrestrial habitats, and, in aquatic environments, to ambient limitations of carbon. Evidence is reviewed for its presence in five genera of aquatic vascular plants, including Isoëtes, Sagitteria, Vallisneria, Crassula and Littorella. Initially, aquatic CAM was considered by some to be an oxymoron, but some aquatic species have been studied in sufficient detail to say definitively they posses CAM photosynthesis. CO2 concentrating mechanisms in photosynthetic organs require a barrier to leakage; e.g., terrestrial C4 plants have suberized bundle sheath cells and terrestrial CAM plants high stomatal resistance. In aquatic CAM plants the primary barrier to CO2 leakage is the extremely high diffusional resistance of water. This, coupled with the sink provided by extensive intercellular gas space, generate daytime CO2(pi) comparable to terrestrial CAM plants. CAM contributes to the carbon budget by both net carbon gain and carbon recycling, and the magnitude of each is environmentally influenced. Aquatic CAM plants inhabit sites where photosynthesis is potentially limited by carbon. Many occupy moderately fertile shallow temporary pools that experience extreme diel fluctuations in carbon availability. CAM plants are able to take advantage of elevated nighttime CO2 levels in these habitats. This gives them a competitive advantage over non(CAM species that are carbon starved during the day and an advantage over species that expend energy in membrane transport of bicarbonate. Some aquatic CAM plants are distributed in highly infertile lakes, where extreme carbon limitation and light are important selective factors. Compilation of reports on diel changes in titratable acidity and malate show 69 out of 180 species have significant overnight accumulation, although evidence is presented discounting CAM in some. It is concluded that similar proportions of the aquatic and terrestrial floras have evolved CAM photosynthesis. Aquatic Isoëtes (Lycophyta) represent the oldest lineage of CAM plants and cladistic analysis supports an origin for CAM in seasonal wetlands, from which it has radiated into oligotrophic lakes and into terrestrial habitats. Temperate Zone terrestrial species share many characteristics with amphibious ancestors, which in their temporary terrestrial stage, produce functional stomata and switch from CAM to C3. Many lacustrine Isoëtes have retained the phenotypic plasticity of amphibious species and can adapt to an aerial environment by development of stomata and switching to C3. However, in some Neotropical alpine species, adaptations to the lacustrine environment are genetically fixed and these constitutive species fail to produce stomata or loose CAM when artificially maintained in an aerial environment. It is hypothesized that neotropical lacustrine species may be more ancient in origin and have given rise to terrestrial species, which have retained most of the characteristics of their aquatic ancestry, including astomatous leaves, CAM and sediment(based carbon nutrition. Click Here to Go to Back to Top
ARE BIOTIC FACTORS SIGNIFICANT IN INFLUENCING THE DISTRIBUTION OF HALOPHYTES IN SALINE HABITATS? Irwin A. Ungar Department of Environmental and Plant Biology Ohio University Athens, Ohio 45701 I. Abstract II. Introduction III. Competition IV. Allelopathy V. Chemical Inhibition VI. Herbivory VII. Parasitism VIII. Conclusions IX. Acknowledgments X. Literature Cited I. Abstract The influence of biotic factors on the distribution and establishment of halophytes are being considered in this review. Physico-chemical factors, such as salinity and flooding, often are considered to be the determining factors controlling the establishment and zonational patterns of species in salt marsh and salt desert environments. Sharp boundaries commonly are found between halophyte communities even though there is a gradual change in the physico-chemical environment, which indicates that biotic interactions may play a significant role in determining the distribution pattern of species and the composition of zonal communities. Competition is hypothesized to play a key role in determining both the upper and lower limits of species distribution along a salinity gradient. Field and laboratory experiments indicate that the upper limits of distribution of halophytes into less saline or nonsaline habitats is often determined by competition. There appears to be a reciprocal relationship between the level of salt tolerance of species and their ability to compete with glycophytes in less saline habitats. Halophytes are not competitive in nonsaline habitats, but their competitive ability increases sharply in saline habitats. Allelopathic effects have been reported in salt desert habitats, but have not been reported along salinity gradients in salt marshes. Some species of halophytes that are salt accumulators have the ability to change soil chemistry. Chemical inhibition of intolerant species occurs when high concentrations of sodium are concentrated in the surface soils of salt desert plant communities that are dominated by salt accumulating species. Establishment of less salt tolerant species is inhibited in the vicinity of these salt accumulating species. Herbivory is reported to cause both an increase or decrease in plant diversity in salt marsh habitats. Heavy grazing is reported to eliminate sensitive species and produce a dense cover of graminoids in high marsh coastal habitats. However, in other marshes grazing produced bare patches that allowed annuals and other low marsh species to invade upper marsh zonal communities. A retrogression in plant succession may occur in salt marshes and salt deserts because of heavy grazing. Intermediate levels of grazing by sheep, cattle, and horses could produce communities with the highest species richness and heterogeneity. Grazing by geese produced bare areas that had soils with higher salinity and lower soil moisture than vegetated areas, allowing only the more salt tolerant species to persist. Removal of geese from areas by use of inclosures caused an increase in species richness in sub-arctic salt marshses. Invertebrate herbivores could also inhibit the survival of seeds and the ability of plants to establish in marshes. Parasites could play a significant role in determining the species composition of zonal communities, because uninfected rarer species are able to establish in the gaps produced by the death of parasitized species. Click Here to Go to Back to Top
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Steps toward better scientific illustrations. Ed. 2. Allen Press, Lawrence, Kansas. Alston, R. E. 1968. The genetics of phenolic compounds. Pages 171-204 in J. B. Harborne (ed.), Biochemistry of phenolic compounds. Academic Press, New York. CBE Style Manual Committee. 1983. CBE style manual: A guide for authors, editors, and publishers in the biological sciences. Ed. 5. Council of Biology Editors, Bethesda, Maryland. Dahlgren, R. M. T., H. T. Clifford & F. F. Yeo. 1985. The families of monocotyledons: structure, evolution, and taxonomy. Springer-Verlag, New York. Funk, V. A. 1982. Systematics of Montanoa Cerv. (Compositae). Mem. New York Bot. Gard. 36:1-133. _____& D. R. Brooks. 198 1. Advances in cladistics. The New York Botanical Garden, Bronx, New York. Gifford, E. M. & A. S. Foster. 1988. Morphology and evolution of vascular plants. Ed. 3. W. H. Freeman, New York. Takhtajan, A. 1980. Outline of the classification of flowering plants (Magnoliophyta). Bot. Rev. 46:225-359. 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Send original illustrations and/or high-quality black-and-white glossy photographs or photostats of them. Click Here to Go to Back to Top