Root biomechanics in Rhizophora mangle: anatomy,morphology and ecology of mangrove’s flying buttresses

Background and Aims Rhizophora species of mangroves have a conspicuous system of stilt-like roots (rhizophores) that grow from the main stem and resemble flying buttresses. As such, the development of rhizophores can be predicted to be important for the effective transmission of dynamic loads from the top of the tree to the ground, especially where the substrate is unstable, as is often the case in the habitats where Rhizophora species typically grow. This study tests the hypothesis that rhizophore architecture in R. mangle co-varies with their proximity to the main stem, and with stem size and crown position.Methods The allometry and wood mechanical properties of R. mangle (red mangrove) trees growing in a mangrove basin forest within a coastal lagoon in Mexico were compared with those of coexisting, non-buttressed mangrove trees of Avicennia germinans. The anatomy of rhizophores was related to mechanical stress due to crown orientation (static load) and to prevailing winds (dynamic load) at the study site.Key Results Rhizophores buttressed between 10 and 33 % of tree height. There were significant and direct scaling relationships between the number, height and length of rhizophores vs. basal area, tree height and crown area. Wood mechanical resistance was significantly higher in the buttressed R. mangle (modulus of elasticity, MOE = 18·1 ± 2 GPa) than in A. germinans (MOE = 12·1 ± 0·5 GPa). Slenderness ratios (total height/stem diameter) were higher in R. mangle, but there were no interspecies differences in critical buckling height. When in proximity to the main stem, rhizophores had a lower length/height ratio, higher eccentricity and higher xylem/bark and pith proportions. However, there were no directional trends with regard to prevailing winds or tree leaning.Conclusions In comparison with A. germinans, a tree species with wide girth and flare at the base, R. mangle supports a thinner stem of higher mechanical resistance that is stabilized by rhizophores resembling flying buttresses. This provides a unique strategy to increase tree slenderness and height in the typically unstable substrate on which the trees grow, at a site that is subject to frequent storms.     

Distribution of mangrove vegetation along inundation, phosphorus, and salinity gradients on the Bragança Peninsula in Northern Brazil

Background and aims

The Bragança Peninsula, in northern Brazil is characterized by macrotides (4 m) and specific edaphic conditions, which determine the local mangrove forest’s development. This study, conducted during the dry season evaluated the spatial patterns of Rhizophora mangle and Avicennia germinans species across an inundation gradient.

Methods

Along a transect of 700 m, measurements of structure forest, soil moisture, porewater salinity, extractable phosphorus (extr.-P) in sediments, and phosphorus in the leaves (leaf-P) were conducted.

Result

The A. germinans (100 %) occurred in high intertidal (HI) zone. A. germinans (59 %) and R. mangle (41 %) co-occurred in mid intertidal (MI) zone, while R. mangle (58 %) predominated in low intertidal (LI) zone, followed by A. germinans (37 %) and Laguncularia racemosa (5 %). Covariance analysis (ANCOVA) indicated that salinity and soil moisture means are significantly different between the mangrove forests, but do not correlate with inundation frequency (IF). The means of extr.-P were significantly different in mangrove forests and correlated with IF and leaf-P.

Conclusion

The inundation frequency, the availability of P in the sediments, phosphorus in the leaves and interstitial salinity are all important factors contributing to the distribution of the mangrove tree species A. germinans and R. mangle on the Bragança Peninsula.     

Increasing fluctuations of soil salinity affect seedling growth performances and physiology in three Neotropical mangrove species

Background

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity.

Aims and methods

The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl).

Results

Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production.

Conclusions

This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings’ morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage.     

Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: A field‐based experiment

Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.     

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.     

Colletotrichum gigasporum sp. nov., a new species of Colletotrichum producing long straight conidia

A new species of Colletotrichum was described, based on morphology and phylogeny. The fungus was isolated in Madagascar from healthy leaves of Centella asiatica, in Mexico from wild native of Stylosanthes guianensis and in Colombia from Coffea arabica. The fungus differed from the currently related species in the genus by its longer and wider size of conidia. In potato dextrose agar medium supplemented with sterilized leaf powder of Ce. asiatica, the fungus produced fertile perithecia containing asci and unusual long ascospores measuring up to 90 μm. In addition to these morphological characteristics, the maximum parsimony analysis of the ITS region and β-tubulin gene placed the fungus in a distinct clade far from the currently valid Colletotrichum species. Based on the morphological and molecular characterization, Colletotrichum gigasporum sp. nov. was proposed as a new species in the genus Colletotrichum Corda.     

Herbivore feeding preferences as measured by leaf damage and stomatal ingestion: a mangrove crab example

The diet of the mangrove crab, Aratus pisonii, was assessed by determining the percent of damaged leaves at selected mangrove communities and by examining herbivore gut contents. This study compared the utility of both methods and tested if comparable levels of damage and dietary preference occurred using the methods. Percent of damaged leaves was determined for the three species of mangroves within Tampa Bay, FL, USA, including: the red, black, and white mangroves (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa, respectively) in four 5×10-m quadrats during summer 2001. For each species, in each of the quadrats, 200 leaves per tree were assessed for the presence or absence of crab damage. A. pisonii were sampled from the same quadrats from which leaf damage data were collected. Stomach contents were dissected and food items were classified into a number of categories.Species damaged and preferred were determined by comparing relative numbers of mangrove leaf stomata from the three mangrove species in gut contents. Results suggested that both methods provide similar estimates of preference. R. mangle leaves were preferred over those of A. germinans and L. racemosa. The percent of R. mangle leaves with damage was about 20-30 times greater than the other species, and R. mangle leaf stomata were 3 to 20 times more abundant in crab guts compared to leaf stomata of the other species. Gut contents indicated that A. pisonii is omnivorous, that average-sized adult crabs (1.4-1.7-cm width) prefer R. mangle, and that the diet of males is more varied than of females. While use of both percent leaf damage and crab gut contents reliably indicates preference, gut contents may describe better the actual diet and elucidate trends for different size or sex classes within a population.     

Genetic variation of <Emphasis Type="Italic">Colletotrichum magnum</Emphasis> isolated from <Emphasis Type="Italic">Carica papaya</Emphasis> as revealed by DNA fingerprinting

Mexico is one of the five largest producers of papaya worldwide, but losses caused by pathogens, mainly fungus, at the pre- and post-harvest stages are often more than 50% of the crop. Papaya anthracnose, caused by three different species of the Colletotrichum genus in Mexico, occupies a preponderant place in this problem. Although two of these species, C. gloeosporiodes and C. truncatum, have been characterized morphologically and genotypically, this has not occurred with C. magnum, the third species involved, about which there is very little information. Because of this, it is vital to know its genetic characterization, much more so considering that the studies carried out on the other two species reveal a wide genetic diversity, differences in pathogenicity and in the response to fungicides of the different strains characterized. In this work, Colletotrichum spp. isolates were collected at different papaya orchards in the south-southeast of Mexico. C. magnum isolates identified by species-specific primers were characterized by morphological and molecular approaches. Differences in colony characteristics resulted in five morphological groups. AP-PCR, DAMD and ISSR markers were found to be very efficient for revealing the interspecific variability of this species. The high genetic variability found in the accessions of C. magnum was linked to the geographical area where they were collected. Isolates from Chiapas State were the most variable, showing point mutations in the ITS1-ITS2 region. These results will enable a better phytosanitary management of anthracnose in papaya in this region of Mexico.     

<Emphasis Type="Italic">Verrucosispora rhizosphaerae</Emphasis> sp. nov., isolated from mangrove rhizosphere soil

An actinomycete strain, 2603PH03^T, was isolated from a mangrove rhizosphere soil sample collected in Wenchang, China. Phylogenetic analysis of the 16S rRNA gene sequence of strain 2603PH03^T indicated high similarity to Verrucosispora gifthornensis DSM 44337^T (99.4%), Verrucosispora andamanensis (99.4%), Verrucosispora fiedleri MG-37^T (99.4%) and Verrucosispora maris AB18-032^T (99.4%). The cell wall was found to contain meso-diaminopimelic acid and glycine. The major menaquinones were identified as MK-9(H₄), MK-9(H₆) and MK-9(H₈), with MK-9(H₂), MK-10(H₂), MK-9(H₁₀) and MK-10(H₆) as minor components. The characteristic whole cell sugars were found to be xylose and mannose. The phospholipid profile was found to contain phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol mannoside, phosphatidylinositol, phosphatidylserine and an unidentified phospholipid. The DNA G+C content was determined to be 70.1 mol%. The results of physiological and biochemical tests and low DNA-DNA relatedness readily distinguished the isolate from the closely related species. On the basis of these phenotypic and genotypic data, strain 2603PH03^T is concluded to represent a novel species of the genus Verrucosispora, for which the name Verrucosispora rhizosphaerae sp. nov. is proposed. The type strain is 2603PH03^T (=CCTCC AA 2016023^T = DSM 45673^T).     

Why species delimitation matters for fungal ecology: Colletotrichum diversity on wild and cultivated cashew in Brazil

Anthracnose is one of the most important plant diseases globally, occurring on a wide range of cultivated and wild host species. This study aimed to identify the Colletotrichum species associated with cashew anthracnose in Brazil, determine their phylogenetic relationships and geographical distribution, and provide some insight into the factors that may be influencing community composition. Colletotrichum isolates collected from symptomatic leaves, stems, inflorescences, and fruit of cultivated and wild cashew, across four Brazilian biomes, were identified as Colletotrichum chrysophilum, Colletotrichum fragariae, Colletotrichum fructicola, Colletotrichum gloeosporioides sensu stricto, Colletotrichum queenslandicum, Colletotrichum siamense and Colletotrichum tropicale. Colletotrichum siamense was the most dominant species. The greatest species richness was associated with cultivated cashew; leaves harbored more species than the other organs; the Atlantic Forest encompassed more species than the other biomes; and Pernambuco was the most species-rich location. However, accounting for the relative abundance of Colletotrichum species and differences in sample size across strata, the interpretation of which community is most diverse depends on how species are delimited. The present study provides valuable information about the Colletotrichum/cashew pathosystem, sheds light on the causal agents identification,and highlights the impact that species delimitation can have on ecological studies of fungi.     

Comparative lipid profiling of two endophytic fungal isolates--Colletotrichum sp. and Alternaria sp. having potential utilities as biodiesel feedstock

Lipid accumulation abilities of two endophytic fungal isolates - Colletotrichum sp. and Alternaria sp. grown under optimum and nutrient-stress conditions were investigated and compared. Significant variations in lipid contents, ranging from 30% to 58% of their dry biomass were found in liquid culture using various carbon sources. Since, >50% of the total lipid was estimated to be neutral lipid for both the fungal species, predicted biodiesel properties were theoretically calculated based upon the determined fatty acid profiles; and the values were found to be comparable to those of commonly used plant oils for biodiesel production. The two endophytes grew successfully on the combined rice straw and wheat bran as substrate that was degraded by their secretory enzymes including cellulase [1.21-2.51 FPU/g dry substrate (gds)] in solid state fermentation and produced substantial amount of lipid (60.32-84.30 mg/gds). Our study highlights the potential utilities of these two novel endophytic fungi as biodiesel feedstock.     

Evaluation of triterpenols and sterols as organic matter biomarkers in a mangrove ecosystem in northern Brazil

Mangrove leaves, sediment, and excrementfrom the mangrove crab Ucidescordatus from the coastal areas of theBragança peninsula in North Brazil wereanalysed to determine suitable biomarkersfor mangrove-derived organic matter. Leavesof Rhizophora mangle (red mangrove),the dominant species in the area, werecharacterised by high amounts of-amyrin, germanicol, taraxerol, andlupeol. Avicennia germinans (blackmangrove) mainly contained betulin, lupeol,and -sitosterol, whereas significantquantities of -sitosterol and lupeolwere typical of Laguncularia racemosa(white mangrove), the locally leastabundant species. Except for betulin, theexcrement of U. cordatus containedall of the above substances, but moststrongly reflected the triterpenolsignature of R. mangle leaves, thepredominant diet of this crab. Surfacesediments from various mangrove locationshad relatively uniform compositions thatpossibly reflect tidal mixing. Sedimentextracts were dominated by taraxerol andcontained smaller amounts of-amyrin, germanicol, and lupeol.Only sediments in a marsh area, dominatedby Sporobolus virginicus (seashoredropseed) and Eleocharis sp. (spikerush), revealed a differentbiomarker distribution. Core samples ofsubrecent sediment (up to 4000 ¹⁴C yrBP), for which previous pollen analysisindicated vegetation dominated bymangroves, had compositions similar to thatof the surface sediment. Taraxerol was themain component in the examined mangrovesediments and may be a marker for mangrovematter in this region, although analysis ofplant material did not unequivocallysupport this. Germanicol is suggested to bea biomarker for organic matter from R.mangle in North Brazil. It was detected inolder sediments, and was not significantlyaffected by ingestion by land crabs.     

Reproductive phenology and physiological traits in the red mangrove hybrid complex (Rhizophora mangle and R. racemosa) across a natural gradient of nutrients and salinity

Factors modulating introgressive hybridization between the red mangrove species Rhizophora mangle and R. racemosa in spatially defined sites are poorly understood. To investigate this, we evaluated the reproductive phenology and the nutrient and physiological traits in those two species and their F₁ hybrids genotyped with microsatellite data across a natural hybrid zone from the Pacific coast of Panama. We found no evidence that reproductive phenology represents a barrier to gene flow, because R. mangle and the F₁ hybrids produced flowers and propagules throughout the annual cycle, while R. racemosa flowered only in the dry season. Soil nutrient concentrations decreased landward, while soil salinity varied only slightly. Foliar nutrients and δ¹⁵N signatures varied according to the soil nutrient gradient, but only foliar phosphorus and carbon varied among species. In contrast, two structural variables (height and trunk diameter) and leaf variables related to salinity tolerance (Na, Cl:Na, K:Na, cation:anion) and water-use efficiency (i.e., δ¹³C) differed among species, suggesting higher salinity tolerance for R. mangle and F₁ hybrids compared with R. racemosa. We conclude that parental species and F₁ hybrids differ in salinity tolerance and water-use efficiency, which could be associated with adaptive evolution of the red mangrove hybrid complex.     

Flowering patterns in three neotropical mangrove species: Evidence from a Caribbean island

The present study sought to identify the factors that drive flowering in the main neotropical mangrove species. We evaluated the effects of water regime variables and foliar meristematic activity on the flowering intensity of Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans in three physiographic types of San Andres Island, Colombia. The results show that pore salinity regulates flowering intensity and periodicity in all three mangrove species. All species flowering showed significant correlations with water balance and air vapor pressure deficit (VPD). In the fringe and interior mangroves, R. mangle flowering was explained linearly by salinity (25%) and monthly change in salinity (47%), respectively. L. racemosa flowering was linked with stronger periods of foliar meristematic activity and occurred during months of relatively high water balance (54-233 mm) and low VPD (1.18-1.29 kPa). The flowering of A. germinans was triggered by water deficit conditions when the monthly pore salinity increased over 30 g L⁻¹ and, with a month delay response, when the water column height (WCH) was below ground. The flowering of A. germinans was also explained by these variables at 65% and 39%, respectively. The flowering patterns of the studied mangrove species indicate that reproduction within the neotropical mangrove community depends on seasonally contrasting water conditions on an annual basis.     

<Emphasis Type="Italic">Acuminatispora palmarum</Emphasis> gen. et sp. nov. from mangrove habitats

Fungi play a vital role as decomposers in mangrove ecosystems. A new ascomycete species, Acuminatispora palmarum, inhabiting decayed petioles and rachides of palms in mangrove habitats, is introduced in this paper based on morphological and phylogenetic evidence. Phylogenetic relationships of related taxa were inferred from combined LSU, SSU, TEF1α, and RPB2 sequence data, and the analyses indicate that A. palmarum could be recognized as a distinct group in Pleosporales, but its familial placement needs to be further resolved. The morphological characters of this new taxon are also different from other members in Pleosporales by its deeply immersed ascomata, long pedicellate asci, and biseriate to triseriate, 1-(rarely 3) septate, brown, fusiform ascospores with acute or narrowly pointed ending cells. Acuminatispora gen. nov. (Pleosporales, incertae sedis) is therefore established to accommodate the new taxon A. palmarum. Furthermore, phylogenetic relationships of Acrocordiopsis and Caryospora are discussed with a consideration of morphological observations.     

<Emphasis Type="Italic">Colletotrichum atractylodicola</Emphasis> sp. nov.: the anthracnose pathogen of <Emphasis Type="Italic">Atractylodes chinensis</Emphasis> in China

A new anthracnose disease of Atractylodes chinensis was observed in Liaoning province in China. The causal agent was isolated from diseased leaves. Based on morphology and ITS sequence data, it was identified as a Colletotrichum species belonging to the C. destructivum species complex. A multi-locus DNA sequence analysis (ITS, GAPDH, CHS-1, ACT, TUB2) revealed that the fungus represents a new species that is described here as C. atractylodicola sp. nov. Pathogenicity tests confirmed that the isolated species is the causal agent of the observed anthracnose symptoms on A. chinensis leaves.     

Mangrove habitat partitioning by Ucides cordatus (Ucididae): effects of the degree of tidal flooding and tree-species composition during its life cycle

Environmental factors strongly affect mangrove crabs, and some factors modulate population structure and habitat partitioning during the crabs’ life cycle. However, the effect of these environmental factors on habitat selection by mangrove crabs is still unknown. We evaluated habitat selection by the mangrove crab Ucides cordatus in mangrove forests with different degrees of predominance of Rhizophora mangle, Laguncularia racemosa or Avicennia schaueriana, two tidal flooding levels (less- and more-flooded), and two biological periods (breeding and non-breeding seasons). Sampling was conducted in four mangrove forests with different influences of these biotic and abiotic parameters. We used the data for sex ratio to explain environmental partitioning by this species. Females predominated in R. mangle mangroves, independently of the biological period (breeding or non-breeding seasons), and males predominated only in the less-flooded L. racemosa mangroves. The flooding level affected the sex ratio of U. cordatus, with a predominance of males in less-flooded mangroves, independently of the biological period; and a gender balance in the more-flooded mangroves only during the breeding season. Outside the breeding season, the largest specimens were recorded in the R. mangle mangroves, but in the breeding season, the largest crabs were recorded in the L. racemosa mangroves with a higher level of flooding. These results suggest that tree-species composition and tidal flooding level can have a significant effect on the habitat partitioning of sexes and sizes of the mangrove crab U. cordatus both during and outside the breeding season.     

Distribution of arbuscular mycorrhizal fungi in four semi-mangrove plant communities

To better understand the diversity and species composition of arbuscular mycorrhizal fungi (AMF) in mangrove ecosystems, the AMF colonization and distribution in four semi-mangrove plant communities were investigated. Typical AMF hyphal, vesicle and arbuscular structures were commonly observed in all the root samples, indicating that AMF are important components on the landward fringe of mangrove habitats. AMF spores were extracted from the rhizospheric soils, and an SSU rDNA fragment from each spore morph-type was amplified and sequenced for species identification. AMF species composition and diversity in the roots of each semi-mangrove species were also analyzed based on an SSU-ITS-LSU fragment, which was amplified, cloned and sequenced from root samples. In total, 11 unique AMF sequences were obtained from spores and 172 from roots. Phylogenetic analyses indicated that the sequences from the soil and roots were grouped into 5 and 14 phylotypes, respectively. AMF from six genera including Acaulospora, Claroideoglomus, Diversispora, Funneliformis, Paraglomus, and Rhizophagus were identified, with a further six phylotypes from the Glomeraceae family that could not be identified to the genus level. The AMF genus composition in the investigated semi-mangrove communities was very similar to that in the intertidal zone of this mangrove ecosystem and other investigated mangrove ecosystems, implying possible fungal adaptation to mangrove conditions.