Micropropagation of grey mangrove Avicennia marina

This study was conducted to develop a micropropagation protocol for grey mangrove, Avicennia marina (Forsk.)     

Salinity, growth and root respiration in the grey mangrove, Avicennia marina

Relationships between growth parameters and root respiration under various conditions of salinity were investigated in seedlings of the grey mangrove Avicennia marina (Forsk.) Vierh. Growth, root/shoot ratios, leaf succulence and osmotic potential of leaves were measured for seedlings grown for 6–8 weeks in 100, 50, 25 and 0% seawater. Oxygen uptake of root segments, from distal to proximal ends of roots, was measured for all treatments. Total growth was maximal in 25% seawater, highest leaf succulence was obtained in 50% seawater, and highest leaf osmotic potential in 100% seawater. Oxygen uptake in distal root segments, as measured both by Clark oxygen electrode and Warburg manometry, showed a stimulation in the presence of salt that closely paralleled growth stimulation. The rates of respiration were highest in 25% seawater. The oxygen uptake was not stimulated by salt per se, since concentrations higher than 25% were associated with a decline in rate of oxygen uptake from the maximum. Values for the respiratory quotient approximated to one in all treatments. Avicennia marina has been reported to exclude from its roots about 90% of the salt in the surrounding medium. It might have been expected that increased concentrations of salt in the growth medium would be associated with a standard salt respiration response in the roots; however, this was not obtained.     

The intertidal distribution of the grey mangrove (Avicennia marina) in southeastern Australia: The effects of physical conditions,interspecific competition,and predation on propagule establishment and survival

Abstract The upper and lower limits of the distribution of mature Avicennia marina lie between mean high water and mean sea level in open estuaries in southeastern Australia. Newly established seedlings are highly variable in abundance, but are rarely found in the saltmarsh or on mudflats. Their distribution is unlikely to be limited by dispersal because propagules disperse into the saltmarsh and to intertidal mudflats, but their establishment may be limited by physicochemical conditions, interspecific competition and predation. The model that physicochemical conditions control the intertidal limits of establishment of seedlings was accepted for propagules stranding in the saltmarsh but rejected for those stranding on mudflats. No seedlings established on saltmarsh sediments but similar numbers of seedlings established within light gaps in adult mangrove stands and on intertidal mudflats. The model that interspecific interaction with freeliving macroalgae (Hormosira banksii) reduces the establishment of seedlings on mudflats covered with macroalgae or in stands with a ground cover of macroalgae was accepted. Under controlled conditions five times as many propagules established on cleared ground compared with ground covered with macroalgae. Predators also reduce seedling establishment, but the model that they preferentially act on propagules stranding on the mudflat was rejected. The low number of seedlings found on mudflats without macroalgae appears to relate to wave and current effects on establishment and the effects of waterlogging or fouling on survival.     

Factors contributing to dwarfing in the mangrove Avicennia marina

BACKGROUND AND AIMS: In Richards Bay, South Africa, Avicennia marina frequently exhibits a distinct productivity gradient, with tree height decreasing markedly from 6-10 m in the fringe zone to <1.5 m in the dwarf zone which is 120 m inland at a slightly higher elevation. In this investigation, soil physico-chemical conditions between fringe and dwarf A. marina were compared and the constraints imposed by any differences on mangrove ecophysiology and productivity determined. METHODS: Soil and plant samples were analysed for inorganic ions using spectrophotometry. Gas exchange measurements were taken with an infrared gas analyser and chlorophyll fluorescence with a fluorometer. Xylem psi was determined with a pressure chamber and chlorophyll content with a chlorophyll absorbance meter. RESULTS: In the dwarf site, soil salinity, total cations, electrical conductivity and soil concentrations of Na(+), K(+), Ca(2+), Mg(2+), Zn(2+), Mn(2+) and Cu(2+) were significantly higher than those in the fringe zone. Soil water potential and the concentration of soil P, however, were significantly lower in the dwarf site. In the leaves, Na(+) was the predominant ion and its concentration was 24 % higher in dwarf than fringe mangroves. Leaf concentrations of K(+), Ca(2+), Mg(2+), Mn(2+) and P, however, were significantly lower in dwarf mangroves. Photosynthetic performance, measured by gas exchange and chlorophyll fluorescence, was significantly reduced in the dwarf plants. CONCLUSIONS: The results suggest that hydro-edaphic factors contribute to high soil salinities, low water potentials, water stress and ion imbalance within tissues including P deficiency, which in interaction, contribute to dwarfing in Avicennia marina.     

Ventilation and respiration in roots of one-year-old seedlings of grey mangrove Avicennia marina (Forsk.) Vierh.

Avicennia marina (Forsk.) Vierh. was grown from seed for 12 months in artificially tidal tanks providing a range of duration and depth of inundation. Plant growth characteristics were measured at harvest. Root aerenchyma development was estimated by pycnometry, root respiration rates by manometry, and the oxygen supply capacity of the above-ground portions of the plant was determined using oxygen electrode chambers. The mass per plant at harvest was influenced by the extent of inundation during growth with maximal growth at intermediate-length (1.5 to 6.5 h per tide) inundation periods. Those plants that had been submerged the longest (8.5 h per tide) had the least root tissue. The oxygen conductance of the stem base plus any pneumatophores showed a maximum in plants grown under intermediate inundation. Oxygen demand and internal gas space per unit dry weight of root were independent of extent of inundation. During high tide the plants grown at inundation periods of more than about 3–5 hours per tide were likely to become anaerobic. This may constitute a physiological limit for this species at the bottom of the tidal range.     

Growth and establishment of mangrove (Avicennia marina) on the coastlines of Kuwait

Mangrove (Avicennia marina) communities constitute an importantcomponent of the renewable natural vegetation resources of the coastalzones of the Arabian Gulf south of Kuwait. Attempts to introduce themangrove into the intertidal zones of the coastline of Kuwait are underwaybecause of the expected favorable environmental impact of this plant, andbecause of its moderating influence on the local climate and enhancementof the aesthetic and recreational value of the coastlines and fisheryresources. Propagules were collected from natural stands of mangrove inBahrain and the United Arab Emirates. Silvicultural practices were followedto produce healthy plants after growing of propagules in the greenhouse.Observations indicated that there is a positive correlation betweenpropagule weight and the length of the seedling stem. Outplanting wasdone in two sites in the intertidal zone around the Sulabikhat Bay, Kuwait.Data on plant survival showed that the most suitable level for successfulestablishment of mangrove was around or below the 3-meter contour tidalline. After 7 years of growth, plants reached a mean height of 250 cm,which is close to the height of their parent trees in Bahrain. The U.A.E.stock plants reached 288 cm after 5 years of growth in Kuwait. Plantsflowered and produced viable seeds. The biological feasibility ofestablishing mangrove plantations in the intertidal flats of Kuwait's coastlineswas documented from the field observation of the experimental plantations.Studies to document the environmental impact of the introduction areunderway.     

白骨壤模拟湿地系统中Pb的分布、迁移及其净化效应

在温室中建立红树林植物白骨壤模拟湿地系统,分别用正常(NW)、5倍(FW)和10倍(TW)浓度人工配置的城市污水每周定时定量对模拟系统污灌2次,用海水作对照(CL),持续1年。研究重金属Pb在湿地系统中的分布、迁移及其被净化的效果。结果表明：加入系统中的Pb主要存留于土壤子系统中,很少迁移到植物体和凋落物中：植物各器官中的Pb含量在根中最高;模拟系统对重金属。Pb的净化效果显著,各污水处理组分别为：NW组97．97％、FW组97．86％、TW组98．06％。根据物质平衡模型计算得土壤子系统。Pb的环境容量较大,因此整个模拟系统对Pb污染的承受力较大。     

Isolation of several anti-stress genes from a mangrove plant Avicennia marina

In order to isolate anti-stress genes from mangrove plants, a cDNA library of Avicennia marina was constructed and screened for anti-stress genes by a functional expression screening with Escherichia coli cells. Several stress-related gene homologues, such as chaperonin-60, clpP protease of the clp/Hsp 100 family of chaperones, ubiquitin, eEF1A, drought-induced AtDi19 gene of Arabidopsis thaliana, and secretory peroxidase, were successfully isolated.     

Low salinities adversely affect photosynthetic performance of the mangrove,Avicennia marina

Photosynthetic performance of the highly salt tolerant mangrove, Avicennia marina, was compared at two sites differing insubstrate soil salinities. Carbon dioxide exchange and chlorophyll fluorescence weremonitored at a high salinity site in Durban Bay (35) and at a low salinitysite in Beachwood (< 12). Mean CO₂ exchange, conductanceand transpiration were consistently higher at the high salinity site. Carbondioxide response curves indicated that carboxylation efficiency was higherand stomatal limitation lower at the Durban Bay site. PSII quantum yield,electron transport rates (ETR) and intrinsic PSII efficiency(F_v/F_m) were significantly higher at the high salinity site.Quenching analysis indicated a higher degree ofphotoinhibition/photoprotection in leaves at the low salinity site. Predawnand midday leaf water potentials were –1.6 and –3.1 MPa at Beachwood,compared to –2.6 and –3.8 MPa, respectively, at Durban Bay. Leafconcentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺,Cl^- and N were significantly higher at Durban Bay. Photosyntheticperformance is apparently impaired at the low salinity site in Beachwood asa result of K⁺ and N deficiencies in the leaves.     

The regeneration niche of the grey mangrove (Avicennia marina): effects of salinity,light and sediment factors on establishment,growth and survival in the field

Field observations of seedlings and saplings of Avicennia marina showed patterns that correlated with salinity, light and sediment. Models that account for these observations were subsequently tested in a series of field experiments. Establishment varied within an estuary under controlled conditions but was not related to salinity or sediment type. Seedling survival was uniform over 3 years regardless of position in estuary and sediment type. Seedling densities and survival under canopies or in canopy gaps were not significantly different. However, seedling growth and density of saplings were greater in canopy gaps. Experiments involving manipulations of canopies showed no differences in seedling survival under canopies or in light gaps, but addition of slow-release fertilizer enhanced growth and survival in canopy gaps and under canopies. Long-term comparison of areas denuded of a canopy and with sediment disturbance showed enhanced establishment and survival when compared with areas with canopy gaps but with undisturbed sediments. Overall there appears to be no restriction to establishment of propagules within mangrove stands other than the supply of propagules and tidal or wave action. In contrast, recruitment to the sapling stage appears to be restricted by light and sediment resources. We suggest that propagules need to establish in a regeneration niche for seedling recruitment to the sapling stage. This differs from the view that seedlings in the under-storey are analogous to a seed pool in the soil.     

Effects of stand size on pollination in temperate populations of the mangrove Avicennia marina

Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size, reflecting both natural and anthropogenic fragmentation. We hypothesised that, as observed in many terrestrial forests, small stands (<100 plants) would experience lower pollinator densities and altered pollinator behaviour and visitation and, in consequence, would display reduced pollen deposition as compared with large stands (>10,000 plants). Nevertheless, we recognise that such predictions may be overly simplistic because within this region A. marina attracts a diversity of flower visitors, but its only significant pollinator is the exotic honeybee Apis mellifera. Moreover, it is unclear how readily A. mellifera moves among groups of plants within different mangrove stands of varying sizes separated either by water or urban habitat matrix. Our detailed surveys within pairs of large and small stands in two locations support the predictions that pollinator density and pollen deposition are reduced or altered within small stands. Within small stands honeybee abundance and pollen deposition were on average reduced significantly by 84 and 61 %, respectively. Moreover, within small stands there was a non-significant 12 % increase in the mean time that honeybees spent foraging on individual plants and hence potentially depositing self pollen. Taken together, our data indicate that fragmentation affects the performance of A. mellifera as a pollinator of A. marina and reduce pollinator abundance, leading to pollen limitation in small as compared to large stands, which may negatively affect reproductive output.     

The excavation and cultivation in containers of mature grey mangroves,Avicennia marina

The grey mangrove, Avicennia marina, grows in intertidal habitat that is under pressure from expanding human settlement and industry along coastlines in the tropics and subtropics. Inappropriate clearing, and also the dieback of large stands of A. marina associated with pollution, have created an interest in methods for revegetation and also the need for a better understanding of the species physiological tolerances including to herbicide residue. Eco-toxicological studies have so far been exclusively on seedlings because of perceived difficulties cultivating mature plants in controlled environments. Reforestation projects are often associated with low rates of establishment, because of the susceptibility of propagules, seedlings and saplings to wind and wave erosion, as well as flooding and desiccation associated with the natural inter-tidal environment. We report on the successful excavation, and cultivation in containers with an automated irrigation system of eight mature A. marina plants. It is possible to transplant mature mangroves and achieve significant vegetative growth and also flowering and fruiting within the first year. It is difficult to compare the likely costs of transplanting a more limited number of mature plants to many propagules. However, we suggest that in situations where reforestation with young propagules, seedlings or saplings has failed because of excessive wash, drowning or smothering, the transplanting of mature mangroves could be a better option.     

The population dynamics of the mangrove Avicennia marina; demographic synthesis and predictive modelling

Population dynamics of the widespread mangrove Avicennia marina was studied over the complete life-history from zygotes through to adults in southeastern Australia. Zygote survival, propagule dispersal, seedling establishment, seedling recruitment and sapling recruitment were examined by demographic censuses over a range of spatial and temporal scales. Hypotheses about factors regulating survival were tested by manipulative field experiments. Life table statistics for survival and fecundity were used to calculate transition probabilities and their variance for seven stages of life history. These parameters were used as the basis of a stochastic model that predicts population structure after small and large scale perturbations.     

Genetic structure at range edge: low diversity and high inbreeding in Southeast Asian mangrove (Avicennia marina) populations

Understanding the genetic composition and mating systems of edge populations provides important insights into the environmental and demographic factors shaping species' distribution ranges. We analysed samples of the mangrove Avicennia marina from Vietnam, northern Philippines and Australia, with microsatellite markers. We compared genetic diversity and structure in edge (Southeast Asia, and Southern Australia) and core (North and Eastern Australia) populations, and also compared our results with previously published data from core and southern edge populations. Comparisons highlighted significantly reduced gene diversity and higher genetic structure in both margins compared to core populations, which can be attributed to very low effective population size, pollinator scarcity and high environmental pressure at distribution margins. The estimated level of inbreeding was significantly higher in northeastern populations compared to core and southern populations. This suggests that despite the high genetic load usually associated with inbreeding, inbreeding or even selfing may be advantageous in margin habitats due to the possible advantages of reproductive assurance, or local adaptation. The very high level of genetic structure and inbreeding show that populations of A. marina are functioning as independent evolutionary units more than as components of a metapopulation system connected by gene flow. The combinations of those characteristics make these peripheral populations likely to develop local adaptations and therefore to be of particular interest for conservation strategies as well as for adaptation to possible future environmental changes.     

Characterisation and analysis of microsatellite loci in a mangrove species, Avicennia marina (Forsk.) Vierh. (Avicenniaceae)

An enriched microsatellite library of the mangrove species Avicennia marina was constructed, in which 85.8% of the clones contained microsatellite sequences. Of the microsatellite repeat sequences isolated, 55.0% were di-nucleotides, 34.2% were tri-nucleotides, 50.0% were perfect, 24.2% were imperfect, and 15.0% were compound. Four different di-nucleotide repeats were isolated with repeat lengths ranging from 5 to 33; ten different tri-nucleotide repeats were isolated with repeat lengths ranging from 3 to 25. The most common di-nucleotide was the AC/TG repeat; the most common tri-nucleotide was the CCG/GGC repeat. Sixteen microsatellite sequences were selected for primer design, and 6 primers were selected to investigate the polymorphism detected among 15 individuals of A. marina from three natural populations in Australia. A total of 40 alleles were detected at 6 microsatellite loci. The number of alleles per microsatellite locus ranged from 5 to 13. On average, 7 alleles were detected per locus. All microsatellite loci showed high levels of gene diversity (heterozygosity), with values ranging from 0.53 to 0.88; the mean value of gene diversity was 0.70. Microsatellite loci were also tested for conservation across Avicennia species. There was a decline in amplification success with increasing divergence between Avicennia species. The results indicate that microsatellites are abundant in the Avicennia genome and can be valuable genetic markers for assessing the effects of deforestation and forest fragmentation in mangrove communities, which is an important issue for mangrove conservation and afforestation schemes. Received: 8 June 1999 / Accepted: 21 September 1999     

Comparative analysis of genetic diversity in the mangrove species Avicennia marina (Forsk.) Vierh. (Avicenniaceae) detected by AFLPs and SSRs

Avicennia marina is an important mangrove species with a wide geographical and climatic distribution which suggests that large amounts of genetic diversity are available for conservation and breeding programs. In this study we compare the informativeness of AFLPs and SSRs for assessing genetic diversity within and among individuals, populations and subspecies of A. marina in Australia. Our comparison utilized three SSR loci and three AFLP primer sets that were known to be polymorphic, and could be run in a single analysis on a capillary electrophoresis system, using different- colored fluorescent dyes. A total of 120 individuals representing six populations and three subspecies were sampled. At the locus level, SSRs were considerably more variable than AFLPs, with a total of 52 alleles and an average heterozygosity of 0.78. Average heterozygosity for AFLPs was 0.193, but all of the 918 bands scored were polymorphic. Thus, AFLPs were considerably more efficient at revealing polymorphic loci than SSRs despite lower average heterozygosities. SSRs detected more genetic differentiation between populations (19 vs 9%) and subspecies (35 vs 11%) than AFLPs. Principal co-ordinate analysis revealed congruent patterns of genetic relationships at the individual, population and subspecific levels for both data sets. Mantel testing confirmed congruence between AFLP and SSR genetic distances among, but not within, population comparisons, indicating that the markers were segregating independently but that evolutionary groups (populations and subspecies) were similar. Three genetic criteria of importance for defining priorities for ex situ collections or in situ conservation programs (number of alleles, number of locally common alleles and number of private alleles) were correlated between the AFLP and SSR data sets. The congruence between AFLP and SSR data sets suggest that either method, or a combination, is applicable to expanded genetic studies of mangroves. The codominant nature of SSRs makes them ideal for further population-based investigations, such as mating-system analyses, for which the dominant AFLP markers are less well suited. AFLPs may be particularly useful for monitoring propagation programs and identifying duplicates within collections, since a single PCR assay can reveal many loci at once. Received: 3 October 2000 / Accepted: 19 February 2001     

Frugivory by insects on mangrove propagules: effects on the early life history of Avicennia marina

This study investigates how herbivory by larval insects on fruit of the mangrove Avicennia marina affects the subsequent establishment, growth, and survivorship of its seedlings. Research was done in a temperate mangrove forest in Australia where the larvae of two species of insects were the dominant frugivores: the mangrove fruit fly Euphranta marina and the mangrove plume moth Cenoloba obliteralis. Larvae consumed the cotyledons of fruit, but not their embryonic axes. Damage to the cotyledons of fruit while on the tree was obvious in abscised propagules and the cotyledons of seedlings, indicating that larvae within fruit continue to consume the cotyledons and develop while the propagule disperses and the seedling establishes. We found that 53% of fruit, 69% of abscised propagules, and 80% of the cotyledons of seedlings had been attacked by larval insects. The degree of damage to the cotyledons was positively related to the densities of larvae within the fruit and the number of emergence or exit holes in the surface of the cotyledons. Consequently, the number of exit holes could be used as a proxy for the amount of damage to the cotyledons. An experiment in which we placed propagules with different levels of damage (zero, one, two, or three exit holes) on the forest floor revealed that frugivory did not influence the establishment of seedlings. In another experiment, we monitored the performance of newly established seedlings with cotyledons that had zero exit holes, one or more exit holes, or where we had removed their cotyledons. In both experiments, the growth of seedlings as measured by their heights and number of leaves was negatively related to the degree of frugivory. Consumption of the cotyledons by larvae apparently reduces the energy reserves available for the initial growth of seedlings. The early mortality of seedlings in both experiments was minimal and appeared to be independent of differences in size due to frugivory. Experimentally removing the cotyledons of seedlings produced extremely short seedlings with increased mortality, confirming the importance of cotyledonary reserves to the initial growth and survivorship of seedlings of A. marina. This study highlights how the early life history of plants may be impacted by conditions experienced by the propagules before they disperse from the parental plant.