Molecular identification of natural mangrove hybrids of Rhizophora in Peninsular Malaysia

Natural hybridization is common in plants. Very often, the identity of a putative hybrid is inferred based on the observation of morphological features intermediate between two possible parental species occurring in a specific location. However, due to plasticity of morphological features and the co-occurrence of more than two possible parental species, molecular markers would be most useful to establish the origin of a putative hybrid. In mangroves, three Rhizophora species (Rhizophora apiculata, Rhizophora mucronata, and Rhizophora stylosa) and two putative hybrids (Rhizophora × lamarckii and Rhizophora × annamalayana) are distributed in the Indo-West Pacific region. Leaf samples of Rhizophora were obtained from two locations in Peninsular Malaysia, namely, Bagan Lalang and Pulau Burung, where all three species grow in sympatry. We analyzed sequences of one chloroplast and six nuclear DNA regions. Our results confirmed earlier claims that the morphologically identified putative hybrids growing in Pulau Burung are R. × lamarckii, a cross between R. apiculata and R. stylosa. Our data also pointed to the possible discovery of a new Rhizophora hybrid—a cross between R. mucronata and R. stylosa—the identification of which would have been difficult based on morphological features alone. The directions and the stages of hybridization are also discussed.     

Soil salinity and pH in Japanese mangrove forests and growth of cultivated mangrove plants in different soil conditions

Soil conditions of mangrove forests in southern Japan were found to correlate largely with zonal distributions of the species.Kandelia candel grew in soils with low salinity and low pH,Avicennia marina, Rhizophora stylosa andSonneratia alba in soils with high salinity and high pH, andBruguiera gymnorrhiza in soil with a wide range of pH but limited range of salinity.Lumnitzera racemosa colonized soil with a wide range of pH and medium salinity. Seedlings ofKandelia candel, Bruguiera gymnorrhiza andRhizophora stylosa were planted in soils with differing salinity and pH. Optimum seedling growth ofKandelia, Bruguiera andRhizophora occurred when plants were cultivated in soils similar to those of their natural habitats, suggesting that growth of mangrove species and their zonal distributions were regulated by salinity and soil pH.     

The abundance and growth of Avicennia marina and Rhizophora stylosa in the low shore zone of Darwin Harbour,Northern Territory

Abstract The growth and distribution of the two mangrove seedling species, Avicennia marina (Forsk.) Vierh. and Rhizophora stylosa Griff., were studied in the low-shore zone at three locations along two estuaries of Darwin Harbour to determine how growth varied along the estuary and within the habitats of the low shore zone. The low shore environment was heterogenous for factors such as salinity and light, with substantial variation within and between locations. Seedlings of Avicennia were in higher densities in light gaps than in the adjacent forest, and density in both habitats decreased towards the mouth of the estuary. Growth of Avicennia seedlings, as measured through in situ growth trials and plant harvests, increased towards the mouth of the estuary. Results for Rhizophora seedlings were more complex although some similar trends were evident. This may have been due to the greater early survival of Rhizophora seedlings compared to Avicennia seedlings. The importance of propagule origin was investigated, for Rhizophora, by transplanting propagules between locations along one estuary. Increased seedling survival was observed at the propagule source site; however, this effect was subtle and probably not the most important factor affecting seedling survival at a site.     

Effects of light and intertidal position on seedling survival and growth in tropical tidal forests

Reciprocal transplant experiments were used to study the effects of tidal inundation and light level on growth and survival of four species of mangroves in Australia: Avicennia marina (Forsk.) Vierh., Bruguiera gymnorrhiza (L.) Lam., Ceriops tagal C.T. White, and Rhizophora stylosa Griff. Seedlings were planted in the high or low intertidal and in light gaps or under the shade of a closed canopy. Survival and growth of the seedlings were monitored for 30–36 months. Significant differences in survival were found among species, between intertidal zones and due to light level. Averaged across intertidal zones and light level, survival was greatest for Rhizophora and decreased in the order Ceriops, Avicennia, and Bruguiera. For all species survival was greater (P ⩽ 0.001) in the high than in the low intertidal treatment, regardless of light level. Within the high intertidal all species survived better in light gaps than under the canopy. Relative growth of Rhizophora stylosa, Avicennia marina, and Ceriops tagal were greater in the high versus low intertidal and in gaps versus under the canopy. For Bruguiera gymnorrhiza growth was not significantly different between gap and canopy or high and low intertidal. Although Avicennia marina, Bruguiera gymnorrhiza, and Rhizophora stylosa survived and/or grew best in the high intertidal they reach maximum abundance in the low intertidal. Ceriops tagal, however, performed best in the region where it is most abundant, yet even there, it was out-performed by the former three species. These results indicate that the species zonation patterns often observed across the intertidal cannot be explained by physiological adaptation alone. Factors such as propagule dispersal, competition and predation on propagules may also be important.     

Chloroplast microsatellite markers for the mangrove tree species Bruguiera gymnorrhiza, Kandelia candel, and Rhizophora stylosa, and cross-amplification in other mangrove species

Chloroplast microsatellite (cpSSR) markers were developed for three ecologically and economically important tree species in the mangrove family, Rhizophoraceae: Bruguiera gymnorrhiza, Kandelia candel, and Rhizophora stylosa. Noncoding regions of chloroplast DNA (cpDNA) from each species were separately amplified using universal chloroplast primers. Six, two, and three polymorphic cpSSR loci in B. gymnorrhiza, K. candel, and R. stylosa, respectively, were developed from amplified noncoding cpDNA regions. Characterization of 216, 156, and 253 individuals of B. gymnorrhiza, K. candel, and R. stylosa, respectively, collected from different natural mangrove populations (B. gymnorrhiza, 9; K. candel, 7; R. stylosa, 9) on Iriomote Island in Japan showed that these loci provide cpSSR markers with polymorphisms ranging from two to four alleles per locus and gene diversity between 0.027 and 0.480. These cpSSR markers will be useful for analyzing the maternal lineage distributions and population genetic structures of the three species. Several of these markers may also be useful in similar studies of other mangrove species.     

Location and interseasonal variation in flowering, propagule setting and propagule size in mangroves species of the family Rhizophoraceae

Three species of mangroves, Rhizophora stylosa, Rhizophora mangle (synonym R. samoensis) and Bruguiera gymnorhiza in the family Rhizophoraceae were studied to understand the flowering pattern, propagule development and the propagule size at maturity prior to dispersal from the mother plant. The study was conducted in the Wet and the Dry zones over two seasons in Viti Levu, the Main Island of Fiji. The flower number, number of propagules and propagule size at maturity were significantly different among three species and within species in the Dry and the Wet zones. Only 1–2% of total flowers in each species became mature propagules. This percentage was significantly lower in the Dry zone for all three species. Rhizophora stylosa produced the biggest size of propagules followed by Rhizophora mangle and Bruguiera gymnorhiza. Relatively longer and heavier propagules were recorded in the Wet zone and shorter and lighter in the Dry zone. Inter-seasonal differences were not significant for these characters. This could be mainly due to almost similar amount of rainfall, relative humidity and temperature regimes over two seasons within each zone.     

Litter production and seasonality of mangroves in Papua New Guinea

Productivity, as measured by litter trapping, of a mangrove dominated by Rhizophora stylosa Griff. at Motupore Island (lat. 9° 31′34′?S; long. 147° 17$\text{\$}\text{?}$02‘ E) was 1430 g dry weight m^?2 year^?1. This is a high figure when compared with other studied mangrove sites. Phenological data were obtained for R. stylosa, R. apiculata Blume and Sonneratia alba Smith. All species have a major leaf fall in the wet season. Flowering in both Rhizophora species is greatest during the wet season, but S. alba peaks during the dry season. Leaf emergence data were only available for R. stylosa and these appeared to be trimodal. Correlations were calculated for each component with rainfall, wind run, maximum temperature and minimum temperature. Some significant correlations were obtained with rainfall and maximum temperature. These correlations are discussed and it is suggested that the seasonality of mangrove phenologies needs to be considered in terms of whole tree physiology rather than isolated environmental factors.     

Quantitative distribution of meiobenthos and the structure of the free-living nematode community of the mangrove intertidal zone in Nha Trang bay (Vietnam) in the South China Sea

Meiobenthic studies were performed in an intertidal area in the Be River estuary (Nha Trang Bay, Vietnam). The study area is an area of riverine-type mangroves that have been heavily damaged by human impacts, including timber cutting and waste. Three biotopes are situated in the middle intertidal zone: a fringe of Rhizophora stylosa, a bush area composed of Avicennia aff. alba behind it, and muddy sand with fiddler crabs (Uca spp.), which is free of mangrove plants. Three replicate samples of meiobenthos were collected in each biotope and each sample was subdivided into two layers: 0–1 and 1–4 cm. The abundance of metazoan meiobenthos varied from 735 specimens/10 cm² in the Uca spp. biotope to 244 specimens/10 cm² beneath the Rhizophora trees. Six taxonomic groups of high rank were found among the meiofauna: Nematoda, Copepoda (Harpacticoida), Oligochaeta, Turbellaria, Kinorhyncha, and Foraminifera (Allogromiida). The spatial variability of meiobenthos and its key taxa was estimated and the spatial distribution patterns of free-living nematode species were described. About 90% of the total meiobenthos inhabited the upper 0–1 cm of the sediments. Nematodes constituted 90–95% of all meiobenthic organisms in the samples. A total of 48 species of free-living nematodes were found in the investigated mangrove intertidal area. In terms of species composition and set of dominants, the nematode community is comprised of three local assemblages: one of them inhabits the uppermost centimeter in the Uca and Avicennia biocenoses; the second assemblage occupies the upper sediment layer in the Rhizophora stand; a less abundant but specific assemblage of several nematode species occurs in the subsurface sediments at all three sites.     

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.     

Development of microsatellite markers in Rhizophora stylosa using a dual‐suppression‐polymerase chain reaction technique

Rhizophora stylosa is an ecologically important mangrove tree species that is found in tropical and subtropical regions. We isolated five polymorphic microsatellite loci from R. stylosa using a dual‐suppression‐polymerase chain reaction technique. These loci provided microsatellite markers with polymorphism of four alleles in each locus for overall population. The mean expected heterozygosities ranged from 0.113 to 0.473.     

Pattern and process in mangrove forests of the Andaman Islands

Abatract The structural and functional aspects of mangrove forests of the Andaman Islands were described. The mangrove forests of Andaman are highly diversified and rich in species composition. Twenty-six species were collected, Rhizophora lamarckii and R. stylosa were reported for the first time from these islands. The mangroves of Andaman are very productive in comparison to other forest types. Maximum production of biomass was found in the undisturbed Oralkatcha forest. Maximum litter fall was also found at Oralkatcha.     

Patterns of secondary succession in a mangrove forest of Southern Florida

Summary Successional patterns were studied in mangrove forests which had developed recently in response to salinization of areas formerly supporting freshwater marshes along Biscayne Bay in North Miami, Florida. The population structures of these Induced Forests were compared with an adjacent Historical Forest which consisted of a nearly pure stand ofRhizophora mangle. A mixed forest ofRhizophora andLaguncularia racemosa had developed in intertidal areas, while areas above the mean high water elevation supported a scrub community dominated byLaguncularia. Maximum growth of bothRhizophora andLaguncularia occurred in intertidal areas, while both species were stunted and had sparse, poorly formed canopies in drier environments above the mean high water level. Analysis of population structure suggests that Induced Forests in intertidal areas are undergoing succession to a stand ofRhizophora. Laguncularia is unable to compete effectively withRhizophora in these areas and it is suggested that it eventually will be limited to the drier areas, where competition fromRhizophora will be reduced or absent.formely Kimball     

红海榄内生细菌多样性及其抑制鱼类致病菌活性研究

红海榄为红树科红海属植物,广泛分布于热带海岸的红树林中,为真红树植物的典型代表。该研究以广西山口红树林国家级自然保护区红海榄为对象,应用稀释涂布法和三线法从红海榄各组织中分离出17株内生细菌,通过各菌株形态特征观察及利用16S rRNA序列基因和韦恩图分析其内生细菌多样性。结果表明:17株内生细菌分属3个门5科7属8种,Micromonospora和Mangrovibacter属为其优势类群。进一步分析发现红海榄根茎叶等组织的内生细菌类群差别较大,仅有1个相同菌属,17株菌中有3株菌与已有细菌物种典型菌株的全长16S rRNA基因相似性低于97%,代表着潜在的新属或新种。运用纸片法研究8株内生细菌发酵液的乙酸乙酯提取物对鱼类致病菌副溶血弧菌活性抑制效果,发现3株内生细菌(H003、H013、H009,浓度5 mg·m L-1)的代谢产物对副溶血弧菌具有较强的抑菌活性,其抑菌圈直径分别达到(8.4±0.07)、(8.2±0.07)、(8.3±0.14)mm。该研究结果表明红海榄中具有较好的内生细菌多样性和抑菌活性,为今后研究其内生细菌的化学多样性及其应用提供了重要的物质基础。     

Molecular phylogeny of mangroves VIII: Analysis of mitochondrial DNA variation for species identification and relationships in Indian mangrove Rhizophoraceae

Ten species belonging to four genera of the mangrove tribe Rhizophoreaefound in the Indian subcontinent were analysed for species identification andgenetic relationship using nine mitochondrial gene probes. RFLP patternobservedwith 27 probe enzyme combinations the genera Rhizophora,Bruguiera, Ceriops andKandelia differentiated these species into three classesofmitotypes with further resolution within them. Clustering of these mitotypesindicated that Rhizophora was more closely related toCeriops-Kandelia than to theBruguiera. Though the component species of each genusclustered together, a high degree of heterogeneity was observed among fourspecies of the genus Rhizophora and three species of genusBruguiera. The variation between two species ofCeriops was minimal. Species-specific profiles wereobserved for all the species in some probe-enzyme combination. Though themonotypic genus Kandelia shared a number of loci withgenusCeriops, it remained distinct. The putative parents of thenaturally occuring interspecific hybrid in Pichavaram were reconfirmed to beR. apiculata and R. mucronata. Theresults are discussed with regard to the taxonomic and phylogeneticrelationships between different species and genera of the tribe Rhizophoreae.     

Applications of Multiple Nuclear Genes to the Molecular Phylogeny,Population Genetics and Hybrid Identification in the Mangrove Genus Rhizophora

The genus Rhizophora is one of the most important components of mangrove forests. It is an ideal system for studying biogeography, molecular evolution, population genetics, hybridization and conservation genetics of mangroves. However, there are no sufficient molecular markers to address these topics. Here, we developed 77 pairs of nuclear gene primers, which showed successful PCR amplifications across all five Rhizophora species and sequencing in R. apiculata. Here, we present three tentative applications using a subset of the developed nuclear genes to (I) reconstruct the phylogeny, (II) examine the genetic structure and (III) identify natural hybridization in Rhizophora. Phylogenetic analyses support the hypothesis that Rhizophora had disappeared in the Atlantic-East Pacific (AEP) region and was re-colonized from the IWP region approximately 12.7 Mya. Population genetics analyses in four natural populations of R. apiculata in Hainan, China, revealed extremely low genetic diversity, strong population differentiation and extensive admixture, suggesting that the Pleistocene glaciations, particularly the last glacial maximum, greatly influenced the population dynamics of R. apiculata in Hainan. We also verified the hybrid status of a morphologically intermediate individual between R. apiculata and R. stylosa in Hainan. Based on the sequences of five nuclear genes and one chloroplast intergenic spacer, this individual is likely to be an F1 hybrid, with R. stylosa as its maternal parent. The nuclear gene markers developed in this study should be of great value for characterizing the hybridization and introgression patterns in other cases of this genus and testing the role of natural selection using population genomics approaches.     

水稻广亲和性遗传的再研究

水稻广亲和基因的利用是克服亚种间杂种不育性的重要途径。但在广亲和性的遗传上不同研究者的结论不尽一致。以3种有广亲和品种参加的三交组合为研究材料,研究了品种Ketan Nangka的广亲和性遗传。结果表明水稻亚种杂交F1同时存在着雄性不育和雌性不育,但雄性不育对小穗育性的作用大小因组合而异;无论是在雄性不育位点还是雄性不育位点上,Ketan Nangka均具有相对应的中性基因（广亲和基因）;广亲和性的遗传特点与所用的籼粳测验品种间的杂种不育性密切相关;S－5位点的广亲和基因遗传符合单位点孢子体－配子体互作模型。     

Effects of artificial grassland establishment on soil nutrients and carbon properties in a black-soil-type degraded grassland

Despite a growing knowledge of nutrient limitation for mangrove species and how mangroves adapt to low nutrients, there is scant information about the relative importance of N:P ratio and leaf phenolics variability in determining nutrient conservation. In this study, we evaluated possible nutrient conservation strategies of a mangrove Rhizophora stylosa under nutrient limitation. 1. The leaf nutrient concentrations of R. stylosa changed with season, with the highest N concentration in winter and the highest P concentration in spring for both mature and senescent leaves. Leaf N and P concentrations decreased significantly during leaf senescence. Based on N:P ratios R. stylosa forest was N-limited. Accordingly, the nitrogen resorption efficiency (NRE) was significantly higher than phosphorus resorption efficiency (PRE) for the R. stylosa leaves during leaf senescence. The NRE and PRE both reached the highest in the autumn. Average N and P concentrations in the senescent leaves were 0.15% and 0.06% for R. stylosa, respectively, indicating a complete resorption of N and an incomplete resorption of P. There was a significant negative correlation between nitrogen resorption proficiency (NRP) and NRE, meanwhile phosphorus resorption proficiency (PRP) and PRE correlation was also highly significantly. 2. R. stylosa leaves contained relatively high tannin level. Total phenolics, extractable condensed tannins and total condensed tannins contents increased during leaf senescence, and changed between seasons. The lowest concentrations of total phenolics, extractable condensed tannins and total condensed tannins occurred in summer, total phenolics concentrations were inversely related to nitrogen or phosphorus concentrations. 3. Our results confirmed that resorption efficiency during leaf senescence depends on the type of nutrient limitation, and NRE was much higher than PRE under N-limited conditions. R. stylosa forest developed several nutrient conservation strategies in the intertidal coastline surroundings, including high nitrogen resorption efficiency, low nutrient losses and high tannins level.     

Molecular phylogeny of mangroves VII. PCR-RFLP of trnS-psbC and rbcL gene regions in 24 mangrove and mangrove-associate species

Chloroplast DNA (cpDNA) regions, trnS-psbC and rbcL, from 120 individuals of 24 mangrove and mangrove associate species belonging to 11 orders, 13 families and 17 genera of Angiospermae were amplified by the polymerase chain reaction (PCR) and restriction-digested with HaeIII. Analysis of polymorphism in the restriction fragments (PCR-RFLP) revealed 18 classes of restriction banding pattern in trnS-psbC region. This has provided molecular evidence for diversity in the mangrove floral component at the above-species level. Intra-generic variations were observed in three genera, viz. Rhizophora, Avicennia and Suaeda. Species-specific restriction patterns were found in the genera Rhizophora and Suaeda. A natural hybrid belonging to the genus Rhizophora was also analysed, and its restriction pattern was the same as that of a putative parental species.PCR-RFLP analysis of rbcL gene region was less differentiating. However, it showed 13 different classes of restriction patterns and revealed the usefulness of these investigations for genome analysis at a higher taxonomic level. Intra-specific variation was not observed in any of the species in either of the cpDNA regions analysed. This is the first report which describes variations in the chloroplast genome of mangrove species. Received: 20 April 1999 / Accepted: 12 May 1999     

Spatio‐temporal pattern of specific gravity of mangrove diaspore: implications for upstream dispersal

Mangrove plants, which develop highly productive forests on tropical–subtropical coastlines and river estuaries, rely mainly on river and sea water currents for their diaspore dispersal. Mangrove diaspores are basically dispersed in brackish to sea waters; thus whether they sink or float during the dispersal period could be changed dynamically, both spatially and temporally, depending on the salinity to which they are exposed, as well as on their specific gravity (SG). We found that the SG of diaspores of two mangrove species, Rhizophora stylosa and Bruguiera gymnorrhiza, which are dominant species and form a typical zonation (B. gymnorrhiza in inland areas and R. stylosa in more seaward areas) in the study area, changed spatially and temporally. Bruguiera gymnorrhiza gradually lost its SG in accordance with elapsed time, while R. stylosa lost its SG in the first 6 h and gained gradually according to elapsed time. Hydrodynamic simulation of dispersal patterns, in combination with observed specific gravity changes of both diaspores and river water, demonstrated that the spatio‐temporal pattern of specific gravity change was closely related to the difference in dispersal behaviors between the species. The diaspore of B. gymnorrhiza generally disperses upstream, and covers wider ranges than that of R. stylosa, at least in the early phase of dispersal. These dispersal behaviors agreed well with the distribution pattern of the species across estuaries in the study site. To date, hydrochory has been considered to be a mostly passive process governed by the dynamics of water current and subsequent sediment movement, with fixed diaspore characteristics such as shape and buoyancy. The present study shed new light on an active and dynamic process in hydrochory and found that the buoyancy of diaspores may be controlled by changes in their spatial and temporal SG.     

Seedling survivorship,growth, and response to disturbance in Belizean mangal

Species zonation patterns across tidal gradients in mangrove forests are formed by successful seedling establishment and maintained by replacement of adults by conspecific seedlings. These two processes rarely have been examined experimentally in neotropical mangal. We studied survivorship and growth of seedlings of two species of mangrove, Rhizophora mangle L. and Avicennia germinans (L.) Steam, across a tidal gradient in Belize, Central America. Propagules of each species were planted in common gardens at tidal elevations corresponding to lowest low water (LLW), mean water (MW), and highest high water (HHW). Sixty-nine percent of Rhizophora seedlings planted at MW and 56% of those planted at LLW survived 1 year. Forty-seven percent of MW Avicennia seedlings also survived 1 year. No individuals of either species survived at HHW, and neither did any LLW Avicennia seedlings. Among the surviving Rhizophora seedlings, LLW seedlings grew more rapidly in terms of height, diameter, leaf production, and biomass than did MW seedlings. Insect herbivory was twice as high on MW seedlings as on LLW Rhizophora seedlings. We also examined the response of established Rhizophora seedlings to experimental removal of the adult Rhizophora canopy. Seedlings in canopy removal areas had higher survivorship, grew twice as fast, produced more leaves, and had less than half the herbivory of seedlings growing beneath an intact canopy. These results provide insights into underlying causes and maintenance of zonation in Caribbean mangrove forests.