Flower morphometry of Rhizophora mangle (Rhizophoraceae): geographical variation in Mexican populations

We explored the patterns of intra- and interpopulation variation in flower morphology of the red mangrove, Rhizophora mangle. Twelve populations in Mexico were studied: five from the Gulf of Mexico and the Caribbean Sea, and seven from the Pacific Coast. Six metric floral attributes were measured from a sample of 1370 flowers. Significant differences among populations were found for all six attributes. Because floral attributes were all correlated, scores derived from principal factor analysis were used to describe the variation in flower morphology. Two factors explained essentially all of the variance in flower morphology. Corolla and calyx size had a strong effect on factor 1, while gynoecium size had the higher effect on factor 2. Nested analyses of variance on the scores from both factors revealed significant differences among coasts, among populations within coasts, and among plants within populations. Nonetheless, this variation cannot be explained as a result of clinal variation, as indicated by a series of regression analyses. Cluster analysis (UPGMA) showed that a population from the Pacific coast was clustered together with those of the Atlantic, and the arrangement of populations within each coast showed no evident geographical pattern. We propose that frequent events of extinction and recolonization by a few individuals, followed by selfing, may produce differentiation among populations of red mangrove.     

The Pacific palaeogeography of Rhizophora mangle L. (Rhizophoraceae)

ELLISON, J. C, 1991. The Pacific palaeogeography of Rhizophora mangle L. (Rhizophoraceae). The American red mangrove, Rhizophora mangle is disjunct in its occurrence between the Neotropics and an outlier in the south-west Pacific, a distribution which has been speculated upon for over a century. The species is shown to be indigenous in Tonga, the first such evidence from the outlier, with certain identification of abundantly occurring pollen in an early Holocene mangrove peat, that pre-dates the arrival of man by some 2500 years. It is suggested from review of world-wide fossil records that the species crossed the Pacific eastwards during the Eocene, facilitated by land connections resultant from low stands of sea level and before major subsidence of the Pacific plate. Then subsidence of the Pacific plate caused local extinctions on islands of the central and eastern Pacific as they periodically submerged, the species not able to recolonize from either refuges west of the Andesite line or America due to loss of land connections and its poor dispersal capability.     

Rhizophora mangle L. Seedling Development into the Sapling Stage across Resource and Stress Gradients in Subtropical Florida1

Nutrient, light, salinity, soil redox potentials, and other soil characteristics were determined across a range of mangrove forest heights across the South Florida peninsula encompassing large-stature trees (> 10 m) on the west coast and dwarf forms (< 1 m) in the southeast Everglades. Relationships were established between abiotic factors and Rhizophora mangle seedling growth rates in four height (cm) classes, 25-40, > 40-55, > 55–70, and > 70–85. Light in open canopy gaps was an important determinant of seedling growth. Growth rates in gaps (0.32 ± 0.04 to 1.89 ± 0.18 mm/d) were two- to five-fold greater than adjacent closed canopy forests (0.14 ± 0.01 to 0.40 ± 0.07 mm/d). Among open canopy sites, labile soil phosphorus and soil redox potentials were significantly correlated to growth (P < 0.05; r= 0.98 and 0.89, respectively). Interstitial salinity ranged from 0 to 27 ppt across sites, well below hypersaline conditions. Thus, under low salinity stress and high light availabiliry, soil fertility is proposed to be the dominant factor controlling R. mangle seedling development to a sapling stage (> 85 cm) in South Florida mangrove forests. In addition, soil anoxia is hypothesized to be an important stressor in lagoonal-bay estuaries and marsh-mangrove ecotones with minimal tidal exchange.     

Simulated sea level change alters anatomy, physiology, growth, and reproduction of red mangrove (Rhizophora mangle L.)

Tropical coastal forests – mangroves – will be one of the first ecosystems to be affected by altered sea levels accompanying global climate change. Responses of mangrove forests to changing sea levels depend on reactions of individual plants, yet such responses have not been addressed experimentally. We report data from a long-term greenhouse study that assessed physiological and individual growth responses of the dominant neotropical mangrove, Rhizophora mangle, to levels of inundation expected to occur in the Caribbean within 50–100 years. In this study, we grew potted plants in tanks with simulated semidiurnal (twice daily) high tides that approximated current conditions (MW plants), a 16-cm increase in sea level (LW plants), and a 16-cm decrease in sea level (HW plants). The experiment lasted 2½ years, beginning with mangrove seedlings and terminating after plants began to reproduce. Environmental (air temperature, relative humidity, photosynthetically active radiation) and edaphic conditions (pH, redox, soil sulfide) approximated field conditions in Belize, the source locale for the seedlings. HW plants were shorter and narrower, and produced fewer branches and leaves, responses correlated with the development of acid-sulfide soils in their pots. LW plants initially grew more rapidly than MW plants. However, the growth of LW plants slowed dramatically once they reached the sapling stage, and by the end of the experiment, MW plants were 10–20% larger in all measured growth parameters. Plants did not exhibit differences in allometric growth as a function of inundation. Anatomical characteristics of leaves did not differ among treatments. Both foliar C:N and root porosity decreased from LW through MW to HW. Relative to LW and HW plants, MW plants had 1–7% fewer stomata/mm², 6–21% greater maximum photosynthetic rates, 3–23% greater absolute relative growth rates (RGRs), and a 30% higher RGR for a given increase in net assimilation rate. Reduced growth of R. mangle under realistic conditions approximating future inundation depths likely will temper projected increased growth of this species under concomitant increases in the atmospheric concentration of CO₂.     

Isolation and characterization of microsatellite loci in the red mangrove Rhizophora mangle (Rhizophoraceae) and its related species

Fourteen microsatellite markers were isolated from the red mangrove Rhizophora mangle (Rhizophoraceae), a widely distributed mangrove plant in the New World and West Africa. The range of expected heterozygosity of these markers was 0.000–0.672 in the two populations of R. mangle. Cross-species testing was examined for five other species of Rhizophora, and Kandelia candel and Bruguiera gymnorrhiza. All 14 markers could be amplified in R. samoensis, thirteen in R. racemosa, and six markers in all other species of Rhizophora. Our findings greatly increase the utility of these markers.     

Polymorphic dinucleotide microsatellites for the Mediterranean angler species (Lophiidae)

A microsatellite‐enriched genomic library was obtained from black‐bellied angler Lophius budegassa and six polymorphic dinucleotide markers were successfully optimized. These markers showed levels of polymorphism ranging from 0.363 to 0.662 and allele numbers ranging from three to seven. These markers were also found to successfully amplify in the closely related Lophius piscatorius (angler) and thus appear to be useful for genetic stock structure analysis in both species.     

Sun-shade adaptability of the red mangrove,Rhizophora mangle (Rhizophoraceae): Changes through ontogeny at several levels of biological organization

Rhizophora mangle L., the predominant neotropical mangrove species, occupies a gradient from low intertidal swamp margins with high insolation, to shaded sites at highest high water. Across a light gradient, R. mangle shows properties of both “light-demanding” and “shade-tolerant” species, and defies designation according to existing successional paradigms for rain forest trees. The mode and magnitude of its adaptability to light also change through ontogeny as it grows into the canopy. We characterized and compared phenotypic flexibility of R. mangle seedlings, saplings, and tree modules across changing light environments, from the level of leaf anatomy and photosynthesis, through stem and whole-plant architecture. We also examined growth and mortality differences among sun and shade populations of seedlings over 3 yr. Sun and shade seedling populations diverged in terms of four of six leaf anatomy traits (relative thickness of tissue layers and stomatal density), as well as leaf size and shape, specific leaf area (SLA), leaf internode distances, disparity in blade–petiole angles, canopy spread: height ratios, standing leaf numbers, summer (July) photosynthetic light curve shapes, and growth rates. Saplings showed significant sun/shade differences in fewer characters: leaf thickness, SLA, leaf overlap, disparity in bladepetiole angles, standing leaf numbers, stem volume and branching angle (first-order branches only), and summer photosynthesis. In trees, leaf anatomy was insensitive to light environment, but leaf length, width, and SLA, disparities in bladepetiole angles, and summer maximal photosynthetic rates varied among sun and shade leaf populations. Seedling and sapling photosynthetic rates were significantly depressed in winter (December), while photosynthetic rates in tree leaves did not differ in winter and summer. Seasonal and ontogenetic changes in response to light environment are apparent at several levels of biological organization in R. mangle, within constraints of its architectural baiiplan. Such variation has implications for models of stand carbon gain, and suggest that response flexibility may change with plant age.     

Physiological responses of the mangrove Rhizophora mangle grown in the absence and presence of NaCl

Abstract. Propagules of the mangrove, Rhizophora mangle L., were precultivated for 9 months in a greenhouse. The young plants were transferred into unaerated nutrient solutions without and with 200 mol m ³ NaCl and subsequently their growth, their water relations and the photosynthetic properties of their leaves were studied. Growth of the salttreated plants was significantly increased, while the control plants gradually died off after finishing the experiments. The shoot water potential and the stomatal resistance of the leaves were lowered while the chlorophyll contents and the chlorophyll a/b ratio in the leaves of salt-treated plants were increased by NaCl, the net result being an enhanced rate of CO₂ assimilation. The leaves of both sets of plants showed diurnal fluctuations in malic acid concentration which were more pronounced in the leaves of salt treated plants which, additionally, were more succulent. However, the plants showed no net CO₂ fixation at night, indicating that Rhizophora mangle is a CAM-cycling plant. After 200 d of cultivation without or with NaCl, the Na⁺, Cl and K⁺ concentrations in tissues and vacuoles were measured. Energy-dispersive X-ray microprobe analyses on root vacuoles of control plants reveal Na⁺ preference, on those of salt treated plants a strong K⁺ preference. Vacuolar K⁺ concentrations are neither affected by NaCl nor do they vary across the root radius. High vacuolar Na⁺ and Cl concentrations are found in the hypodermis followed by a stepwise decrease towards the inner root cortex cells. Ion concentrations of the photosynthetically active leaf tissues seem to be regulated by (1) radial filtration across the root cortex: (2) ion exchange of the xlem parenchyma cells: and (3) sequestration of Na⁺ and Cl in the hypodermal water storage tissue of the leaves.     

Primary Herbivory by Wood-Boring Insects along an Architectural Gradient of Rhizophora mangle

We investigated the distribution of primary xylovores in Rhizophora mangle (red mangrove) first-order branches, i.e., “twigs”, along an architectural gradient on Belizean mangrove cays. Greater structural diversity in R. mangle architecture, xylovore availability, occurrence of natural enemies, and habitat do not result in variable xylovore species richness. Despite large differences in architectural complexity, tall, fringe, dwarf, and sapling trees host the same set of primary wig borers. However, tall trees support greater diversity and abundance of twig inquilines than other tree forms. Primary twig borers have a key role in structuring these mangrove communities because their galleries and pupal chambers provide habitats for numerous species of secondary xylovores and inquilines. We also measured the amount of leaf area removed from R. mangle's canopy by wood- and leaf-feeding herbivores. Vigorously growing tall and sapling trees sustain greater losses because of twig borers than dwarf trees. However, xylovory in fringe trees was not different from any of the other categories. Cumulative herbivory was greatest in the tall trees. In most cases, leaf-area loss as an indirect or collateral result of primary xylovory equaled or exceeded leaf-area loss as a direct result of folivory.     

Vulnerability of xylem to embolism in a mangrove vs an inland species of Rhizophoraceae

Vulnerability of xylem conduits to cavitation and embolism was compared in two species of Rhizophoraceae, the mangrove Rhizophora mangle L. and the tropical moist-forest Cassipourea elliptica (Sw.) Poir. Cavitation (water column breakage preceeding embolism) was monitored by ultrasonic detection; embolism was quantified by its reduction of xylem hydraulic conductivity. Acoustic data were not predictive of loss in hydraulic conductivity, probably because signals from cavitating vessels were swamped by more numerous ones from cavitating fibers. Rhizophora mangle was the less vulnerable to embolism of the two species, losing 80% of its hydraulic conductivity between – 6.0 and – 7.0 MPa. Cassipourea elliptica lost conductivity in linear proportion to decreasing xylem pressure from – 0.5 to – 7.0 MPa. Species vulnerability correlated closely with physiological demands of habitat; the mangrove Rhizophora mangle had field xylem pressures between – 2.5 and – 4.0 MPa. whereas the minimum for Cassipourea elliptica was – 1.6 MPa. Differences in vulnerability between species could be accounted for by differences in the measured air permeability of intervessel pit membranes. According to this explanation, embolism occurs when air enters a water-filled vessel from a neighboring air-filled one via pores in shared pit membranes.     

Primary Phloem Development in the Shoot Apex of Rhizophora mangle L. (Rhizophoraceae)

The primary phloem in the shoot apex of the mangrove Rhizophora mangle L. is largely confined to the comparatively condensed area between the first three leaf pairs. The main extension zone, surrounded by the stipular sheath of the third leaf pair, contains vascular bundles arranged in a procambial ring and characterized by a well-developed primary phloem and a less advanced xylem. The phloem consists of a great number of sieve elements, an equal number of associated companion cells, and a few phloem-parenchyma cells. The differentiation of the sieve-element protoplast (with e.g., chromatolytic nuclear degeneration, loss of the vacuole and most organelles) proceeds largely according to a well-known pattern. Their P-type plastids, however, form their protein crystals rather late and therefore cannot be used as an early cell marker. Lateral sieve-element walls are distinct from other wall parts and walls of other cells by their heavy nacreous thickenings, the formation of which is shown to be strictly correlated with the occurrence and orderly arrangement of cortical microtubules.     

Polymorphic dinucleotide microsatellites in tongue sole (Cynoglossus semilaevis)

The tongue sole, Cynoglossus semilaevis, is a rare marine flatfish distributed in Chinese coastal waters. From a (GT)_n‐enriched genomic library, 57 microsatellites were isolated and characterized. Seventeen of these loci were polymorphic in a test population with alleles ranging from three to 13, and observed and expected heterozygosities from 0.1613 to 1.0000 and from 0.2126 to 0.8983, respectively. Five loci deviated from the Hardy–Weinberg equilibrium in the sampled population, and linkage disequilibrium between two loci was significant after applying Bonferroni correction. Three additional fish species assessed for cross‐species amplification revealed that only one locus was also polymorphic in one species. These polymorphic microsatellite loci should provide sufficient level of genetic diversity to evaluate the breeding strategy and investigate the fine‐scale population structure in C. semilaevis.     

Disease of Red Mangrove (Rhizophora mangley) in Southwest Puerto Rico Caused by Cytospora rhizophorae1

A high frequency of dieback and mortality was found in Rhizophora mangle (red mangrove) in coastal mangrove forests of southwest Puerto Rico. Eight plots were established in a variety of mangrove environments to assess the extent and severity of the dieback and mortality. The imperfect fungus Cytospora rhizopborae was isolated consistently from stem dieback and associated canker tissues. No other pathogenic microorganisms were isolated. Pathogenicity was demonstrated in greenhouse and field inoculation experiments with C. rhizophorae using young R. mangle seedlings. In field studies of seedlings inoculated, mortality was 33 percent, and greenhouse mortality was as high as 50 percent. Cytospora rhizophorae was isolated consistently from diseased mangrove tissue; the fungus was grown in pure culture and then inoculated into healthy red mangroves, causing cankers. Koch's postulates were fulfilled by infecting R. mangle with C. rhizophorae, producing disease symptoms, and successfully re‐isolating C. rhizophorae from the diseased tissue. This is the first documentation of the pathogenicity of C. rhizophorae associated with mortality in red mangrove. In the coastal mangrove forests of southwest Puerto Rico, C. rhizophorae may play an important role in the frequency of dieback and mortality in R. mangle, producing slow stem diameter growth and causing frequent stem and root wounds.     

Effect of environment and gibberellins on the early growth and development of the red mangrove, Rhizophora mangle L.

Seedlings of the red mangrove, Rhizophora mangle L., were subjected to a variety of salinity, light, and plant growth regulator treatments to examine the influence of these factors on early development. Stem, leaf, and root growth were significantly enhanced in both low salinity seawater and under reduced intensities of solar radiation. Semi-quantitative analyses of GAs by enzyme-linked immunoabsorbant assays (ELISA) suggest that under these conditions the early 3/13 hydroxylation GA₁ biosynthetic pathway is predominant in R. mangle. Concentrations of GA₁ and GA₁₉-like substances were highest in propagules exhibiting enhanced development. Attempts to identify the endogenous GAs by GC-MS were unsuccessful, most likely due to undetermined impurities present in mangroves. Exogenous applications of GA₃ to R. mangle were moderately successful in alleviating shoot growth inhibitions observed at higher salinities and light levels. The role of gibberellins is discussed in terms of metabolic responses to the external environment and possible impacts upon the distribution of this species.     

Tension wood fibers are related to gravitropic movement of red mangrove (Rhizophora mangle) seedlings

Freshly collected viviparous seedlings (propagules) were collected from wild plants of Rhizophora mangle and planted in vertical or horizontal positions. A total of 80 seedlings were examined anatomically at various ages and orientations. After rooting, seedlings reoriented from horizontal to vertical by extreme bending in the hook region of the hypocotyl directly above the basal 1 cm where roots formed. Hypocotyl bending occurred over many months. Trends in position and relative abundance of tension fibers (also called gelatinous fibers) over time were followed. The erection of the seedling was related to increased secondary xylem and the number of tension wood fibers on the upper side of the hook region. However, linear regressions had low coefficient of determination (r ²) values, presumably related to seedlings with high variability. Received: June 18, 2001 / Accepted: October 2, 2001     

Elevated CO2 alters anatomy,physiology, growth,and reproduction of red mangrove (Rhizophora mangle L.)

Mangroves, woody halophytes restricted to protected tropical coasts, form some of the most productive ecosystems in the world, but their capacity to act as a carbon source or sink under climate change is unknown. Their ability to adjust growth or to function as potential carbon sinks under conditions of rising atmospheric CO₂ during global change may affect global carbon cycling, but as yet has not been investigated experimentally. Halophyte responses to CO₂ doubling may be constrained by the need to use carbon conservatively under water-limited conditions, but data are lacking to issue general predictions. We describe the growth, architecture, biomass allocation, anatomy, and photosynthetic physiology of the predominant neotropical mangrove tree, Rhizophora mangle L., grown solitarily in ambient (350 ll^–1) and double-ambient (700 ll^–1) CO₂ concentrations for over 1 year. Mangrove seedlings exhibited significantly increased biomass, total stem length, branching activity, and total leaf area in elevated CO₂. Enhanced total plant biomass under high CO₂ was associated with higher root:shoot ratios, relative growth rates, and net assimilation rates, but few allometric shifts were attributable to CO₂ treatment independent of plant size. Maximal photosynthetic rates were enhanced among high-CO₂ plants while stomatal conductances were lower, but the magnitude of the treatment difference declined over time, and high-CO₂ seedlings showed a lower P_max at 700 ll^–1 CO₂ than low-CO₂ plants transferred to 700 ll^–1 CO₂: possible evidence of downregulation. The relative thicknesses of leaf cell layers were not affected by treatment. Stomatal density decreased as epidermal cells enlarged in elevated CO₂. Foliar chlorophyll, nitrogen, and sodium concentrations were lower in high CO₂. Mangroves grown in high CO₂ were reproductive after only 1 year of growth (fully 2 years before they typically reproduce in the field), produced aerial roots, and showed extensive lignification of the main stem; hence, elevated CO₂ appeared to accelerate maturation as well as growth. Data from this long-term study suggest that certain mangrove growth characters will change flexibly as atmospheric CO₂ increases, and accord with responses previously shown in Rhizophora apiculata. Such results must be integrated with data from sea-level rise studies to yield predictions of mangrove performance under changing climate.     

Eleven new microsatellites for hop (Humulus lupulus L.)

We present a new set of 11 polymorphic microsatellite primer sequences for use with Humulus lupulus. Microsatellite‐enriched libraries for GA_n and GT_n types of repeats were produced. Sequencing of 72 clones revealed 42 unique inserts containing microsatellites, out of which 19 primer pairs were designed and microsatellite amplification was tested on 39 wild hops and cultivars. Eleven primer pairs showed single locus amplification with 2–13 alleles, average 7.2, of which 17 unique alleles were discovered. One primer pair amplified too strong stutter bands, one locus was monomorphic and multilocus amplification was obtained with the remaining six primer pairs.     

Determination of the antimutagenicity of an aqueous extract of Rhizophora mangle L. (Rhizophoraceae), using in vivo and in vitro test systems

An aqueous extract of Rhizophora mangle L. bark is used as raw material in pottery making in the State of Espirito Santo, Brazil. This extract presents large quantities of tannins, compounds possessing antioxidant properties. Tannin antioxidant activity, as a plant chemical defense mechanism in the process of stabilizing free radicals, has been an incentive to studies on anti-mutagenicity. The present work aimed to evaluate possible antimutagenic activity of a R. mangle aqueous extract, using the Allium cepa test-system and micronuclear (MN) assay with blockage of cytokinesis in Chinese hamster ovary cells (CHO-K1). The Allium cepa test-system indicated antimutagenic activity against the damage induced by the mutagenic agent methyl methanesulfonate. A reduction in both MN cell frequency and chromosome breaks occurred in both the pre and post-treatment protocols. The MN testing of CHO-K1 cells revealed anti-mutagenic activity of the R. mangle extract against methyl methanesulfonate and doxorubicin in pre, simultaneous and post-treatment protocols. These results suggest the presence of phyto-constituents in the extract presenting demutagenic and bio-antimutagenic activities. Since the chemical constitution of Rhizophora mangle species presents elevated tannin content, it is highly probable that these compounds are the antimutagenic promoters themselves.