Changes in Ecosystem Nitrogen and Carbon Allocation with Black Mangrove (Avicennia germinans) Encroachment into Spartina alterniflora Salt Marsh

Ecosystems - Increases in temperature are expected to facilitate encroachment of tropical mangrove forests into temperate salt marshes, yet the effects on ecosystem services are understudied. Our...     

Population Genetic Structure of Neotropical Mangrove Species on the Colombian Pacific Coast: Avicennia germinans (Avicenniaceae)1

We investigated the genetic variation of Avicennia germinans using 172 AFLP (Amplified Fragment Length Polymorphism) bands of 45 plants from four localities on the Colombian Pacific coast: 11 from Virudó (Chocó), 10 from La Plata (Valle), 12 from Tumaco (Nariño), and 12 from Chontal (Nariño). AFLP variation among localities (16.2%) was highly significant (AMOVA; P < 0.0001). All the analyses showed that Tumaco was the most genetically distinct locality of the four under study. The other three localities, La Plata, Virudó, and Chontal, apparently form a large single subpopulation with high‐to‐moderate gene flow among localities. We also found the genetic diversity of A. germinans on the Colombian Pacific coast (H_E= 0.251) higher than that estimated by others over the broad geographic range of A. germinans. All these results together show that mangroves on the Colombian Pacific coast deserve a strong investigative effort to improve our ecological, evolutionary, and biogeographic knowledge of this important tropical forest type.     

Development of six microsatellite loci for black mangrove (Avicennia germinans)

We developed six new microsatellite loci for the black mangrove (Avicennia germinans), an important member of wetland communities worldwide. Loci showed moderate to high polymorphism and a survey of four locations [Puerto Rico (Jobos Bay and Luquillo), Mexico, French Guyana] revealed clear regional (and local) population structure. All populations were genetically distinct and the two continental populations showed much higher diversity than the two insular Puerto Rican locations. These loci complement those recently published by Nettel et al. (2005 ) and promise to be valuable for characterizing local and regional population dynamics in the black mangrove.     

Latitudinal Variation in Leaf and Tree Traits of the Mangrove Avicennia germinans (Avicenniaceae) in the Central Region of the Gulf of Mexico

The variation in leaf mass per area, leaf nutrients (% carbon, nitrogen and phosphorus), and the allometric relation between tree height and diameter of the black mangrove, Avicennia germinans, were explored in nine mangrove forests in similar environments along a 5° latitudinal gradient in the central region of the Gulf of Mexico, as indicated by a southward increase in temperature and precipitation. There was no correlation between leaf nitrogen or phosphorus content and latitude. Leaf mass per area and leaf carbon content were positively correlated with latitude and negatively correlated with temperature and annual rainfall, whereas asymptotic tree height and maximum diameter showed the opposite trend. Such patterns suggest a trade-off between leaf traits and tree size which may be constrained by the same environmental factors along a dry-cold to humid-warm latitudinal gradient.     

Characterization of microsatellite markers for the mangrove tree Avicennia germinans L. (Avicenniaceae)

We describe 10 primers for amplification of microsatellite loci for the mangrove, Avicennia germinans. Eight loci were isolated from a DNA sample from the Pacific coast of Baja California, Mexico and two loci were isolated from a DNA sample from the Atlantic coast of Bermuda. Polymorphism was investigated in a population from the Mexican Pacific coast (n = 15) and in four samples scattered throughout the range of the species. Total number of alleles for the species ranged from two to 10. Observed heterozygosity in the Mexican Pacific coast population ranged from 0.27 to 0.60, with two loci having fixed alleles.     

Linking Avicennia germinans (Acanthaceae) architecture to gall richness and abundance in Brazilian Amazon mangroves

The diversity and abundance of gall‐inducing organisms are directly proportional to the structural complexity of the host plant. This hypothesis is controversial for forest environments, such as mangroves. Avicennia germinans (L.), a principal mangrove tree species found in the Neotropical region, is considered to be a superhost for gall‐inducing insects. Using a generalized linear mixed model (GLMM) based on the analysis of 1000 apical branches from 50 A. germinans trees, we examined the diversity and abundance of gall morphotypes (GM), together with the structural attributes of replanted 5‐ to 9‐year‐old mangroves, in the Amazon coast of Brazil. A total of 7602 galls were registered, averaging 1.3 ± 0.4 galls per leaf. Sixteen of the 22 morphotypes identified were found at all study sites. Two gall morphotypes (GM7 and GM4) were the most abundant, representing approximately 40 percent of the total. The structural complexity of the plant (mainly based on the number of leaves) directly affected the abundance and diversity of these organisms. While A. germinans is a superhost, this type of parasitism did not affect plant development or survival. The ample distribution of A. germinans, the formation of monospecific forests, and the high palatability of this plant make it an essential resource for the survival of the gall‐inducing guild in the mangroves of the Neotropics.     

Phosphatidylglycerol Molecular Species in Chilling-Sensitive and Chilling-Resistant Populations of Avicennia germinans (L.) L

Phosphatidylglycerols (PG) from leaves and from roots of a chilling-sensitive(from Belize) and a chilling-tolerant (from Texas) populationof the black mangrove Avicennia germinans (L.) L were comparedwith respect to both their fatty acid and molecular speciescompositions. There were distinct differences between the twopopulations, and also between root and leaf PG of the same population.In leaf extracts the combined totals of palmitic acid and trans-3-hexadecenoicacid—two components thought to be correlated with chillingsensitivity—were not significantly different between thetwo populations. However, the PG in which only those fatty acidswere present, (i.e., dipalmitoyl and l-palmitoyl-2-(trans-3-hexadecenoyl)PG,accounted for a significantly greater proportion of the totalPG in leaves of the chilling-sensitive plants than in the moreresistant population. This trend in molecular species compositionwas not maintained in roots, where PGs were minor components.The findings are in only partial agreement with current ideasconcerning the possible role of specific lipid molecules ofchloroplast membranes in chilling tolerance. (Received May 28, 1984; Accepted September 3, 1984)     

Post-Glacial Expansion and Population Genetic Divergence of Mangrove Species Avicennia germinans (L.) Stearn and Rhizophora mangle L. along the Mexican Coast

Mangrove forests in the Gulf of California, Mexico represent the northernmost populations along the Pacific coast and thus they are likely to be source populations for colonization at higher latitudes as climate becomes more favorable. Today, these populations are relatively small and fragmented and prior research has indicated that they are poor in genetic diversity. Here we set out to investigate whether the low diversity in this region was a result of recent colonization, or fragmentation and genetic drift of once more extensive mangroves due to climatic changes in the recent past. By sampling the two major mangrove species, Rhizophora mangle and Avicennia germinans, along the Pacific and Atlantic coasts of Mexico, we set out to test whether concordant genetic signals could elucidate recent evolution of the ecosystem. Genetic diversity of both mangrove species showed a decreasing trend toward northern latitudes along the Pacific coast. The lowest levels of genetic diversity were found at the range limits around the Gulf of California and the outer Baja California peninsula. Lack of a strong spatial genetic structure in this area and recent northern gene flow in A. germinans suggest recent colonization by this species. On the other hand, lack of a signal of recent northern dispersal in R. mangle, despite the higher dispersal capability of this species, indicates a longer presence of populations, at least in the southern Gulf of California. We suggest that the longer history, together with higher genetic diversity of R. mangle at the range limits, likely provides a gene pool better able to colonize northwards under climate change than A. germinans.     

Ultrastructural features associated with secretion in the salt glands of Frankenia grandifolia (Frankeniaceae) and Avicennia germinans (Avicenniaceae)

Using stereological procedures, a detailed analysis was made from thin section electron micrographs of secreting and nonsecreting salt glands of Frankenia grandifolia (Cham. and Schlecht) and Avicennia germinans (L.) Stem. In F. grandifolia secretory cells, vacuolar volume significantly decreased, while the volume of endoplasmic reticulum increased in secreting glands. Numerous minivacuoles were predominantly located along the periphery of secreting secretory cells, some in apparent fusion with the plasma membrane. No difference was found in mitochondrial volume in the secretory cells between secreting and nonsecreting glands. In A. germinans, there was a significant decrease in vacuolar volume in secreting secretory cells. The volume of the endoplasmic reticulum and mitochondria also increased in these cells. However, no evidence of mini-vacuolar fusion with the plasma membrane was observed. These results indicate that the physical process of secretion may differ between F. grandifolia and A. germinans; in both, however, the ultrastructural observations support the contention that specific structural parameters are correlated with the process of secretion.     

Biotic interactions mediate the expansion of black mangrove (Avicennia germinans) into salt marshes under climate change

Many species are expanding their distributions to higher latitudes due to global warming. Understanding the mechanisms underlying these distribution shifts is critical for better understanding the impacts of climate changes. The climate envelope approach is widely used to model and predict species distribution shifts with changing climates. Biotic interactions between species, however, may also influence species distributions, and a better understanding of biotic interactions could improve predictions based solely on climate envelope models. Along the northern Gulf of Mexico coast, USA, subtropical black mangrove (Avicennia germinans) at the northern limit of its distribution grows sympatrically with temperate salt marsh plants in Florida, Louisiana, and Texas. In recent decades, freeze‐free winters have led to an expansion of black mangrove into salt marshes. We examined how biotic interactions between black mangrove and salt marsh vegetation along the Texas coast varied across (i) a latitudinal gradient (associated with a winter‐temperature gradient); (ii) the elevational gradient within each marsh (which creates different marsh habitats); and (iii) different life history stages of black mangroves (seedlings vs. juvenile trees). Each of these variables affected the strength or nature of biotic interactions between black mangrove and salt marsh vegetation: (i) Salt marsh vegetation facilitated black mangrove seedlings at their high‐latitude distribution limit, but inhibited black mangrove seedlings at lower latitudes; (ii) mangroves performed well at intermediate elevations, but grew and survived poorly in high‐ and low‐marsh habitats; and (iii) the effect of salt marsh vegetation on black mangroves switched from negative to neutral as black mangroves grew from seedlings into juvenile trees. These results indicate that the expansion of black mangroves is mediated by complex biotic interactions. A better understanding of the impacts of climate change on ecological communities requires incorporating context‐dependent biotic interactions into species range models.     

Salt effects on membranes of the hypodermis and mesophyll cells of Avicennia germinans (Avicenniaceae): a freeze-fracture study

Freeze-fracture electron microscopy was used to investigate intramembranous particle (IMP) densities and particle distributions in the plasma membrane and tonoplast of the cells of secreting and nonsecreting leaves of Avicennia germinans (L.) Steam. Intramembranous particle densities of the protoplasmic (P) and exoplasmic (E) face of the plasma membrane and tonoplast were significantly higher in hypodermal cells of secreting leaves than of nonsecreting leaves. In contrast, no significant differences in the frequency of intramembranous particles were found in any membrane faces of secreting or nonsecreting mesophyll cells. However, particle densities were higher in the plasma membrane and tonoplast of the mesophyll cells, compared to the hypodermal cells, with the exception of the P-face of hypodermal plasma membranes of secreting tissue, which had the highest particle density measured. Particle distributions were dispersed and no discernible patterns such as paracrystalline arrays or other multi-IMP structures were observed. Results support the hypothesis that secretion is coupled to changes in membrane ultrastructure, and the possibility that salt secretion is an active process driven by integral membrane proteins such as the H⁺/ATPase. Additionally, the hypodermal cells of the leaf may function as storage reservoirs for salt as well as water, suggesting a regulatory role in salt secretion.     

Nitrogen Addition in a Tibetan Alpine Meadow Increases Intraspecific Variability in Nitrogen Uptake,Leading to Increased Community-level Nitrogen Uptake

Ecosystems - Plant nitrogen (N) uptake is a critical ecosystem function, especially when terrestrial ecosystems are threatened worldwide by increasing anthropogenic N deposition. However, the...     

Microsatellites for the mangrove tree Avicennia germinans (Acanthaceae): Tools for hybridization and mating system studies

? Premise of the study: We developed a new set of microsatellite markers for the black mangrove Avicennia germinans, to provide new informative tools for further studies of the mating system, interspecific hybridization, and population genetics. ? Methods and Results: We used the microsatellite-enriched library approach to isolate and characterize 25 new primer pairs. Sixteen of them are polymorphic, showing a variable degree of variation in A. germinans, while nine were monomorphic in the samples examined. Eight exhibited private alleles in A. schaueriana. ? Conclusions: These results indicate that these new microsatellite markers will be useful molecular tools for further studies of A. germinans and A. schaueriana population genetics, mating systems, and hybridization.     

First report of Avicennia germinans (Acanthaceae) as a larval host of Junonia litoralis (Nymphalidae) causing higher foliar damage in seedlings than trees

Herbivory is considered an important biotic interaction in mangroves. Nevertheless, detailed information on specific plant–herbivore interactions that might have considerable influence in ecological and evolutionary processes is still very poor and fragmented. Herbivory damage was quantified during December 2015 in seedlings and trees in monospecific stands of Avicennia germinans in Laguna Madre of Tamaulipas, Mexico. The use of this mangrove species as a larval host is well documented; however, this is the first report for Junonia litoralis. These lepidopteran larvae consumed, on average, 10.2% of the leaf area; but herbivory was higher on seedlings (mean 15%) than on trees (mean 2.3%). These values are comparable to estimations of 10% mean herbivory damage in other field studies. This indicates that herbivores cause greater damage in seedlings than in trees. Herbivore activity by J. litoralis only occurred in A. germinans and did not affect associated herbs or shrubs of other species. The close interaction between J. litoralis and A. germinans may have profound implications for ecological and evolutionary processes of mangroves and enables a better understanding of ecosystem function and its conservation. Further studies are needed to investigate such interactions and their implications including long-term monitoring of interstitial salinity and leaf chemistry at different stages of growth and maturity of the host species.     

Silicon Alleviation of Cadmium Toxicity in Mangrove (Avicennia marina) in Relation to Cadmium Compartmentation

Mangrove plants seem to be highly tolerant of high levels of heavy-metal pollution. Recently, some researchers have focused on the mechanisms involved in their metal uptake and tolerance. However, the important mechanisms involved are still only partly understood. This investigation studied whether silicon (Si) affected cadmium (Cd) subcellular distribution in the leaves and root tips of Avicennia marina (Forsk.) Vierh seedlings, resulting in the amelioration of the toxicity of Cd. The results showed that Si partly overcame the reduction in growth due to Cd. This amelioration was correlated with a reduction in Cd uptake and alteration of Cd subcellular distribution. The mechanisms of Si amelioration of Cd stress were tissue dependent. In the leaves and root tips, Si reduced Cd concentration in subcellular fractions, Cd mobility, and the concentration of biologically active Cd in the cell wall active space. Si did not change the distribution of Cd between compartments in the leaves, but it increased the proportion of Cd in the cell walls and reduced the proportion of Cd in the symplast of the root tips.     

Nutrient Addition Differentially Affects Ecological Processes of <Emphasis Type="Italic">Avicennia germinans</Emphasis> in Nitrogen versus Phosphorus Limited Mangrove Ecosystems

Nutrient over-enrichment is a major threat to marine environments, but system-specific attributes of coastal ecosystems may result in differences in their sensitivity and susceptibility to eutrophication. We used fertilization experiments in nitrogen (N)- and phosphorus (P)-limited mangrove forests to test the hypothesis that alleviating different kinds of nutrient limitation may have different effects on ecosystem structure and function in natural systems. We compared a broad range of ecological processes to determine if these systems have different thresholds where shifts might occur in nutrient limitation. Growth responses indicated N limitation in Avicennia germinans (black mangrove) forests in the Indian River Lagoon (IRL), Florida, and P limitation at Twin Cays, Belize. When nutrient deficiency was relieved, A. germinans grew out of its stunted form by increasing wood relative to leaf biomass and shoot length relative to lateral growth. At the P-limited site, P enrichment (+P) increased specific leaf area, N resorption, and P uptake, but had no effect on P resorption. At the N-limited site, +N increased both N and P resorption, but did not alter biomass allocation. Herbivory was greater at the P-limited site and was unaffected by +P, whereas +N led to increased herbivory at the N-limited site. The responses to nutrient enrichment depended on the ecological process and limiting nutrient and suggested that N- versus P-limited mangroves do have different thresholds. +P had a greater effect on more ecological processes at Twin Cays than did +N at the IRL, which indicated that the P-limited site was more sensitive to nutrient loading. Because of this sensitivity, eutrophication is more likely to cause a shift in nutrient limitation at P-limited Twin Cays than N-limited IRL.     

Land barriers and open oceans: effects on gene diversity and population structure in Avicennia germinans L. (Avicenniaceae)

Avicennia germinans L. is a widespread mangrove species occupying the west coast of Africa and the Atlantic and Pacific coasts of the Americas from the Bahamas to Brazil and Baja California to Peru. An amplified fragment length polymorphism (AFLP) molecular analysis was carried out to assess genetic architecture within this species and to evaluate the effects of the Atlantic Ocean and the Central American Isthmus (CAI) on population and regional genetic diversity and differentiation. In total, 349 polymorphic AFLP fragments were identified among 144 individuals from 14 populations from the east Atlantic, west Atlantic and east Pacific. Levels of genetic diversity varied considerably among populations, but were generally higher in populations from the east Atlantic. Regional differentiation between the Pacific coast and Atlantic populations was greater than between east and west Atlantic populations, suggesting that the CAI has had an important influence on population genetic structure in this species. The lower level of divergence of east Atlantic from west Atlantic populations suggests some dispersal across the Atlantic Ocean, although migration rates are probably low; Nm from GST equal to 0.41 and accumulation of private and rare alleles in the east Atlantic. Population differentiation did not appear to follow an isolation by distance model and has probably resulted from complex patterns of population bottlenecks, and founder events due to landscape changes during the Pleistocene, particularly in the west Atlantic. The molecular data provide no support for the treatment of east Atlantic populations as a separate species A. africana.