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Thin sections of resin-embedded portions of 10-month-old Avicennia marina seedlings from Botany Bay. A-Longitudinal section of first-order root showing wide elongated gas channels (*) in the cortex (co), few or no gas spaces in the vascular tissue (v) and narrow elongated channels (arrows) in the pith (p). Scale 200 µm. B-Longitudinal section of first-order root cortex showing rows of cells lining elongated gas channels (*). Lignified collapsed cells (arrows) occur at intervals. Scale 50 µm. C-Transverse section of first-order root showing a distribution of gas space typical for A. marina roots. Large channels (*) are present in the cortex and smaller triangular spaces (arrows) in the pith (p). Scale 200 µm. D-Transverse section of first-order root-cortical gas channels (*) showing the appearance of collapsing lignified cells (arrows). Scale 50 µm. E-Longitudinal section of hypocotyl showing wide elongate channels (*) in the cortex (co). Fibres in the vascular tissue are shown at v. Scale 100 µm. F-Longitudinal section of hypocotyl pith showing narrow elongated channels (arrows). Scale 50 µm .
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Gas-spaces form a continuum throughout 10-month-old Avicennia marina seedlings. This has direct connection with the atmosphere via the stomata and spongy mesophyll of the leaves, and via the lenticels that occur on all the internodes and the hypocotyl. There is therefore provision for aeration of the root system prior to the development of pneumato...
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... of gas spaces that is typical for A. marina roots . The greatest volume of gas space was in the cortex . This was in the form of elongated, more or less cylindrical channels that all ran parallel to the long-axis of the organ (Fig . IA, B) . The channels were commonly separated by a single lay- er of small cells arranged in a regular row (Fig . 1B) . Some of these cells were thin walled, non-lignified and roughly isodiametric in transverse section . Oth- ers in the row showed irregular thickened ridges on their walls (Fig . 113, D) ; these stained blue with tolu- idine blue and appeared to be lignified . The number of these lignified cells varied in different roots and in ...
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... that all ran parallel to the long-axis of the organ (Fig . IA, B) . The channels were commonly separated by a single lay- er of small cells arranged in a regular row (Fig . 1B) . Some of these cells were thin walled, non-lignified and roughly isodiametric in transverse section . Oth- ers in the row showed irregular thickened ridges on their walls (Fig . 113, D) ; these stained blue with tolu- idine blue and appeared to be lignified . The number of these lignified cells varied in different roots and in different regions of the same root : in the roots in Fig . 1 about 50% of the cells in the row exhibited this thickening . Many of the cells had irregular shapes . Some of them appeared to have ...
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... non-lignified and roughly isodiametric in transverse section . Oth- ers in the row showed irregular thickened ridges on their walls (Fig . 113, D) ; these stained blue with tolu- idine blue and appeared to be lignified . The number of these lignified cells varied in different roots and in different regions of the same root : in the roots in Fig . 1 about 50% of the cells in the row exhibited this thickening . Many of the cells had irregular shapes . Some of them appeared to have lost their contents and collapsed inwards so that their walls appeared totally flattened ; cells at various stages in this process were apparent (Fig . 1B, D) . In the final stage of collapse the cells ...
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... and in different regions of the same root : in the roots in Fig . 1 about 50% of the cells in the row exhibited this thickening . Many of the cells had irregular shapes . Some of them appeared to have lost their contents and collapsed inwards so that their walls appeared totally flattened ; cells at various stages in this process were apparent (Fig . 1B, D) . In the final stage of collapse the cells formed a thin layer that separated adjacent lon- gitudinal channels (Fig . 1B) . Collapsed cells that had lignified ridges formed a two-to three-pronged scaf- folding when seen in sections . There were frequent gaps between both lignified and unlignified cells in the middle-lamella region so ...
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... . Many of the cells had irregular shapes . Some of them appeared to have lost their contents and collapsed inwards so that their walls appeared totally flattened ; cells at various stages in this process were apparent (Fig . 1B, D) . In the final stage of collapse the cells formed a thin layer that separated adjacent lon- gitudinal channels (Fig . 1B) . Collapsed cells that had lignified ridges formed a two-to three-pronged scaf- folding when seen in sections . There were frequent gaps between both lignified and unlignified cells in the middle-lamella region so that adjacent longitudinal channels were in continuity (Fig . 1A, C) . The amount of gas space diminished in the outermost ...
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... formed a thin layer that separated adjacent lon- gitudinal channels (Fig . 1B) . Collapsed cells that had lignified ridges formed a two-to three-pronged scaf- folding when seen in sections . There were frequent gaps between both lignified and unlignified cells in the middle-lamella region so that adjacent longitudinal channels were in continuity (Fig . 1A, C) . The amount of gas space diminished in the outermost few rows of cells at the root surface ( Fig . 1 C) and in some roots cell division just beneath the epidermis indicated that a cork cambium had formed . Just inside the cortex, delimit- ed by the endodermis, was the vascular cylinder with no obvious aerenchyma (Fig . 1C) . A ...
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... C) . The amount of gas space diminished in the outermost few rows of cells at the root surface ( Fig . 1 C) and in some roots cell division just beneath the epidermis indicated that a cork cambium had formed . Just inside the cortex, delimit- ed by the endodermis, was the vascular cylinder with no obvious aerenchyma (Fig . ...
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... were in continuity (Fig . 1A, C) . The amount of gas space diminished in the outermost few rows of cells at the root surface ( Fig . 1 C) and in some roots cell division just beneath the epidermis indicated that a cork cambium had formed . Just inside the cortex, delimit- ed by the endodermis, was the vascular cylinder with no obvious aerenchyma (Fig . 1C) . A vascular cambi- um had developed . Internal to the vascular cylinder there was a large pith, many cells of which had some- what thickened lignified walls . The pith also contained gas space but there was much less than in the cortex, and it was confined to the triangular spaces in the cell corners as seen in transverse section (Fig ...
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... (Fig . 1C) . A vascular cambi- um had developed . Internal to the vascular cylinder there was a large pith, many cells of which had some- what thickened lignified walls . The pith also contained gas space but there was much less than in the cortex, and it was confined to the triangular spaces in the cell corners as seen in transverse section (Fig . 1C) . These spaces formed narrow elongated channels, much nar- rower than those in the cortex (Fig . IA) . There was an increase in the size of the triangular gas spaces towards the centre of the pith . The fine roots also contained aerenchyma in the cortex ...
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... space in the hypocotyl was again greatest in the cortex (Fig . IE, F) and it similarly consisted of longi- tudinal channels . However there appeared to be much less gas space in the hypocotyl cortex and the channels appeared narrower and less interconnected than in the root (Fig . 1E, cf. IA, B) . Transverse sections showed that the cortical aerenchyma channels were more regu- lar and more widely separated from one another than in the root (Fig . 2A) . In contrast to the root the cells had generally not collapsed, and there were few lignified cells . Like the gas-channels in the root they were con- nected laterally ...
Citations
... Estas raíces se encuentran en al menos seis géneros de mangle Laguncularia (Combretaceae), Hilairanthus, Avicennia (Acanthaceae), Bruguiera (Rhizophoraceae), Xylocarpus (Meliaceae), y Sonneratia (Sonneratiaceae) (Tomlinson, 1986). Algunas especies de mangle poseen una gran cantidad de aerénquima en las raíces para el intercambio de oxígeno, los neumatóforos suelen tardar un par de años en desarrollarse y durante ese tiempo, la única forma de satisfacer la demanda de oxígeno atmosférico de las raíces es mediante órganos aéreos, incluso pueden existir períodos de tiempo en el que los tallos y hojas queden privados de oxígeno (Ashford & Allaway, 1995). En general, los tejidos vegetales (principalmente de raíces) han sido muy estudiados en plantas que están sometidas algún tipo de estrés o son de importancia comercial, por lo que esta investigación propone caracterizar los tejidos epidérmico, fundamental y de conducción de las partes críticas para la respiración (hojas, pecíolos, raíces y 3 neumatóforos) de cinco especies de mangles: Hilairanthus germinans, Laguncularia racemosa, Conocarpus erectus, Rhizophora mangle y R. racemosa. ...
... Cuando el aire es absorbido de la atmósfera, dentro de las hojas se produce una presurización higrométrica, esto hace que se mueva dentro del aerénquima hacia peciolos, tallos y raíces (Evans et al., 2009). Algunas especies de mangle incluso han desarrollado neumatóforos, éstos se encuentran cubiertos de lenticelas que favorecen la aeración del sistema radicular (Ashford & Allaway, 1995). El aerénquima es un tipo de tejido vegetal que permite la difusión rápida y eficiente de oxígeno, debido a que posee enormes espacios aéreos. ...
Los manglares son ecosistemas complejos que se desarrollan en ambientes inundados, hipóxicos,salinos y de suelos poco consolidados, su vegetación dominante comúnmente denominadamangles ha desarrollado características morfológicas y fisiológicas que les permiten subsistir enesos ecosistemas. El presente trabajo se basó en la caracterización de los tejidos vegetativosde los mangles Hilairanthus germinans, Laguncularia racemosa, Conocarpus erectus, Rhizophoramangle y R. racemosa, describiendo sus diferencias histológicas. Para esto se colectaron hojas, lascuales fueron transportadas y mantenidas en frío hasta su procesamiento. Los cortes se realizaronmanualmente, se utilizó FAA (formol, ácido acético y alcohol), azul de metileno y glicerina líquidapara su fijación y montaje. Posteriormente, se observaron los cortes en microscopio óptico de luzy se midieron los tejidos con reglillas micrométricas. Todas las especies analizadas evidenciaronuna cutícula gruesa, abundante tejido esponjoso y vasos de conducción. H. germinans presentóuna gran cantidad de tricomas piriformes tanto en hojas como pecíolos. En las raíces se observógran cantidad de aerénquima exceptuando por Rhizophora, en este género abundó el tejidoesclerenquimático.
... In roots of Caesalpinia peltophoroides (sibipiruna, family Fabaceae) phi thickenings develop more strongly when the plants are flooded (Henrique et al. 2009), and so-called crescent thickenings, perhaps a modified form of phi thickenings were more common in Syzygium samarangense (wax apple, family Myrtaceae) roots grown in water-logged soils than under control conditions (Tuladhar et al. 2015). Phi thickenings and phi-thickening-like structures have also been demonstrated in numerous aquatic and semi-aquatic plant species associated with the development of aerenchyma, including the mangroves Rhizophora mangle (red mangrove, family Rhizophoraceae) (de Menezes 2006; Souza et al. 2014) and Avicennia marina (grey mangrove, family Acanthaceae) (Ashford and Allaway 1995;Allaway et al. 2001) and Bacopa monnierioides and Bacopa salzmannii (waterhyssops, family Plantaginaceae) (Bona and de Morretes 2003). ...
... However, the complex patterns of phi thickenings seen in orchid roots provide an exception to this pattern (Burr and Barthlott 1991;Idris and Collings 2015). Of more significance, however, is that some roots with significant aerenchyma can show radially oriented phi thickenings, as seen in mangroves (Ashford and Allaway 1995;Allaway et al. 2001;de Menezes 2006;Souza et al. 2014) and Bacopa (Bona and de Morretes 2003). We suggested that this unusual orientation might reflect different forces at play within the roots that contain aerenchyma (Aleamotuʻa et al. 2019). ...
Phi thickenings, lignified bands of secondary cell wall encircling root cortical cells, align between adjacent cells to form a complex network that frames the endodermis and central stele. Since their description in numerous angiosperms and gymnosperms in the two decades from the 1860s, there has been little research into the functions of these enigmatic structures. Their cage-like organisation led to speculation that phi thickenings mechanically strengthen the root, but more recent ideas include that they regulate biotic interactions or control ion movements in a manner similar to the Casparian strip. There is, however, sparse direct evidence supporting these suggestions. In this review, we focus on the roles that phi thickenings might play within roots, and although we conclude that the primary function of phi thickenings is to mechanically stiffen the root apex, we emphasise that phi thickenings need not have a single role and that they can be “re-tooled” to perform other functions. We describe several experimental systems for studying phi thickening functions. Geranium and Pelargonium roots, in which phi thickenings form in cortical cells immediately under the epidermis, are well suited for cell biology investigations, whereas the large aerial roots of epiphytic orchids are ideal for investigating root biomechanics. For genetic analysis, however, the differential induction of phi thickenings in Brassica roots in response to water stress or hormones provides a powerful experimental platform to identify regulatory mechanisms and directly test our models of phi thickening functionality. Since phi thickenings typically form in the root apex, we propose that these structures function primarily to strengthen or stiffen the plant root. We reject the concept that phi thickenings function to block ion flows in a manner analogous to the Casparian strip, but instead see the potential for limiting ion flows within the root cortex as drawback to the presence of thickenings. This negative outcome due to the presence of phi thickenings may explain why phi thickenings are only induced in response to specific biotic or abiotic challenges in some species and are not formed constitutively. In some instances, however, phi thickenings may have been “re-tooled” to perform other roles including blocking uptake of ions, notably in the case of Brassicaceae species growing under extreme conditions.
... Under sea level rise, seedlings are the most affected than adults trees. This is because the seedlings may be submerged completely and remain under the water , restricting the gaseous exchange and the light intensity (Ashford and Allaway 1995). Therefore this study was carried out to examine the prolong submergence effect to the mangrove seedlings during sea level rise. ...
Mangroves are threatened by rising sea levels as a consequence of climate change or locally altered coastal hydrology. Prolonged submergence resulting from increased flooding regimes may negatively influence mangrove growth and survival, particularly at the seedling stage. Seedlings from two dominant Malaysian species, Bruguiera gymnorrhiza and Rhizophora apiculata, were exposed to differing durations of flooding in order to simulate a range of sea level rise conditions. This experiment was conducted in the glasshouse for 11 weeks with four flooding treatments: 6 hrs, 18 hrs, 24 hrs and 24 hrs (stagnant). Survival, growth, xylem anatomy and a suite of ecophysiological responses were monitored to quantify and understand plant response to varying degrees of inundation. The ecophysiological measurements comprised leaf chlorophyll content, chlorophyll fluorescence, maximum photosynthetic rate (Amax) and stomatal conductance (gs). Leaf carbohydrate reserves (non-structural carbohydrates, starch and sucrose) and leaf area were also quantified at the end of the experiment, after week 11 (chapter 3). Mangrove seedling survival was 100% under all flooding treatments. Longer flooding significantly increased the seedlings’ height and stem diameter but resulted in fewer leaves produced under long submergence. Morphological adaptations were observed during flooding treatment (i.e. lenticels structure on seedlings stem and adventitious root). Leaf physiological properties (chlorophyll content and chlorophyll fluorescence) exhibited significantly higher values under long submergence, although they showed period of stress during flooding experiment. Maximum photosynthesis rate and stomatal conductance remained higher during the early part of the flooding experiment and lower toward the end of flooding period. Flooding resulted in higher accumulation of total non-structural carbohydrates in B. gymnorrhiza than R. apiculata although the effect was not significant. Plant leaf area was significantly higher under the 24 hour (stagnant) treatment particularly in B. gymnorrhiza seedlings, implying the seedlings expanded their leaf area under long submergence. Overall, most of the response variables were not affected by the flooding treatment and in fact seedlings showed increased growth under high flooding. Seedlings exposed to longer submergence times may suffer from oxygen deficiency, particularly where submergence times approach 24 hrs (as simulated by the 24 hr ‘stagnant’ treatment). To examine how flooding treatments affected the plant stem, xylem anatomy was quantified in both mangrove species. Small segments of the plant apex (3 cm from the shoot tip) and plant stem (12-15 cm from the shoot tip) were examined using light and electron microscopy. Xylem vessel diameter, cell wall thickness, vessel density and vessel hydraulic diameter were quantified. Vessel diameter varied between plant sections and species. Vessel density and lumen area were significantly higher at the plant apex (p < 0.05, p < 0.001 respectively), but vessel hydraulic diameter was significantly higher at plant mid stem (p < 0.001). There were surprisingly few effects on vessel metrics in response to the flooding treatment: at the extreme treatment of 24 hrs flooding, there was marginally, but not significantly, less cell wall thickening in one species (R. apiculata); vessel lumen area increased to a small extent (p > 0.05), but vessel density did not vary among treatments. Overall, the data demonstrate significant differences in xylem anatomy associated with location on the plant (apex or stem), but very minor effects of flooding, at least following the 11 week experimental treatment (chapter 4). This study also investigated the carbon dynamics of a mangrove forest site in Malaysia. Standing stock was quantified along with above- and belowground production at a site on the east coast of the Kelantan delta, Malaysian peninsular during 2014-2016. The above- and below-ground standing biomass of mangrove trees were quantified: although above ground biomass is larger (276.54 t ha-1), the allocation below ground was significant (20.81 t ha-1), the two contributing to a total biomass of 297.35 t ha-1. Aboveground productivity was 4.81 t ha-1 y-1 and belowground productivity was 12.70 t ha-1 y-1, peaking seasonally during the monsoon period in March and December 2015. These values are among the highest recorded for mangrove forests globally and the data also suggested a rapid turnover time for roots, of approximately 19 months. Thus, although standing biomass is higher above ground, more productivity is allocated below ground. Fifty-five percent of the root biomass was found in the top 30 cm and 78% of the roots, in all soil layers, consisted of fine roots (< 3 mm diameter), making the fine root component a particularly important carbon pool in this ecosystem. A positive relationship was found between fine root biomass, sediment carbon and nitrogen content. Soil temperature, salinity and dissolved oxygen were also investigated in relation to belowground production (chapter 5). This study provides evidence that the seedlings of at least these two mangrove species can survive under flooded conditions. This may have occurred here because of high oxygen levels in the experimental conditions, suggesting that negative effects of enhanced flooding in the field could arise from oxygen starvation rather than direct effects of flooding. In addition, it showed very rapid belowground biomass accumulation and turnover in a natural mangrove forest.
... Sediment accumulation and establishment of individual mangrove trees may mitigate some of the impacts of sea level rise. Ashford and Allaway (1995) found that young mangroves are plastic in their response to inundation regimes. There is a continuum of gas space in Avicennia marina seedlings that allows them to obtain oxygen for their root system before they develop pneumatophores (peg roots) and to also determine the typical inundation regime they are growing within. ...
An assessment of potential threats to Samphire Thornbill habitat in the northern Adelaide and Mt Lofty Ranges NRM Region.
Identifying the rapid decline in Shrubby Samphire (Tecticornia arbuscula) throughout South Australia, most likely due to sea-level rise.
... In extreme flooding situations with prolonged submergence of the whole plant, the ability of the plant to respond to the stresses of submergence becomes crucial for its survival (Vervuren et al. 2003). Mangroves, however, are not known to be very tolerant of underwater stress; flooding might therefore be stressful for smaller mangrove seedlings because they would then experience whole-plant submergence, thus facing reduced gaseous exchange and depressed light intensity (Ashford and Allaway 1995). Salinity has also been reported to compound the effect of inundation on the physiological tolerance of mangrove seedlings (Krauss and Allen 2003;Ye et al. 2003Ye et al. , 2005. ...
Flooding and salinity fluctuations are common in mangrove systems. Sometimes these events are long-lasting, persisting several months. With an increased frequency of heavy rainfalls and terrestrial run-off, subsequent floods have been associated with massive mangrove mortality and failure to regenerate in the region. Owing to climate change, these events are expected to be more common in the future. We investigated how three weeks of submergence in water of different salinities affected the photosynthetic rates in seedlings of three common mangroves: Bruguiera gymnorrhiza (L.) Lamk.; Avicennia marina (Forssk.) Vierh.; and Heritiera littoralis Dryand. We found that photosynthesis and survival rates declined with increasing salinity and submergence time for all species. Prolonged submergence caused a significant decline in photosynthetic rates (as electron transport rate – ETR) for B. gymnorrhiza (P ¼ 0.021) and H. littoralis (P ¼ 0.002), whereas significant effects of both salinity (P ¼ 0.003) and submergence (P ¼ 0.023) were observed between species. Maximum diurnal values of ETR declined in the order of A. marina . B. gymnorrhiza . H. littoralis. After submergence, survived seedlings were tended normally, watered twice a day with freshwater. Three seedlings of B. gymnorrhiza from freshwater and 33% seawater treatments and of A. marina from freshwater treatment displayed signs of recovery for the first 3–5 days, but after that they died. We conclude that submergence time and water salinity will affect the performance of mangrove areas, such that areas experiencing prolonged submergence with flooding dominated by saline water might be most severely impacted.
... Ball and Pidsley, 1995), inundation stress (e.g. Ashford and Allaway, 1995), predation on propagules or seedlings (e.g. Mc-Kee, 1995), pre-dispersal frugivory (e.g. ...
Mangroves may grow in an active sedimentary en-vironment and are therefore closely linked to physical coastal processes. Seedlings colonize dynamic tidal flats, after which mangroves have the potential to change their physical envi-ronment by attenuating hydrodynamic energy and trapping sediments. Disturbance from hydrodynamic energy of waves or currents and the resulting sediment dynamics appear to be a critical bottleneck for seedling establishment on tidal flats and at the forest fringe. However, knowledge about the mechanisms at the single plant level and the spatial pattern of disturbance is limited. By means of a flume study, we demon-strate that a surface erosion threshold of as little as 1–3 cm depth can lead to failure of young seedlings. By monitoring accretion/erosion for 8 months along cross-shore transects in southwest Thailand, we show that, especially on the bare mudflat, the physical sediment disturbance regularly exceeds the critical erosion thresholds derived from the flume study. Physical sediment parameters along the same transects were analysed to deduct patterns of hydrodynamic energy attenu-ation. Grain size analysis and erosion/accretion data showed only limited energy dissipation within the fringing Avicen-nia/Sonneratia zone; sediment dynamics only dropped be-low lethal values for seedlings within the denser Rhizophora zone. Overall, present results emphasize that (i) seedling sur-vival is extremely sensitive to physically driven sediment dynamics and (ii) that such physical disturbances are not only present on the tidal flats but can penetrate a signifi-cant distance into the forest. Spatio-temporal patterns in sedi-ment dynamics should hence be considered when conducting restoration of mangrove ecosystems.
... Avicennia marina was selected in this study because it is a widespread mangrove species with a large distribution in South Asia and Australia (Duke, 1991;Lin, 1999). Compared with other mangrove species, A. marina occupy more seaward habitats and exhibit relatively higher waterlogging tolerance, achieving higher survival over a wider tidal range (Ashford and Allaway, 1995;Lin, 1999;He et al., 2007;Xiao et al., 2009). In this study, mangrove growth and biomass were investigated in a field survey to determine the effects of accelerated sea level rise on population structure and productivity. ...
... However, when the canopy was immersed for 2 h or longer, seedlings of the same species either could not survive the 12-hour inundation treatment (after 10 weeks) or maintained significantly lower growth. Ashford and Allaway (1995) reported that the inner parts of A. marina seedlings contain many gas spaces connected to each other that form a continuous exchange with the atmosphere. When the roots are immersed, the gas space continuum will have access to the atmosphere through the stomata, and leaves can serve as a source of photosynthetically-produced oxygen for the seedlings (Laan and Blom, 1990). ...
... Mangrove roots can be characterized on the basis of various structural properties, but by far the most study of mangrove's root structures were not enough to explore the characteristics of their root caps. Most of the study in mangrove's roots were focus on the architecture567, aerenchyma tissue8910, anatomy and morphology111213, gravitropism [6,14,15], the effect of root epibiont complexity [16], degree of shading [17,18], root density [17,19], and gas exchange20212223. The morphology of the root and root cap is determined primarily by the root apical meristem, because typically the radially symmetric meristem forms a cylindrical root. ...
The anatomy of the root caps in four root types of Avicennia marina were studied using conventional histological tech- niques by Ligth Microscopy (LM) in order to relate their development and structure of their function as environmental adaptation in mangrove’s root and to identify cellular polarities with respect to gravity. In columella cells, nuclei are located proximally. The result reveals that root caps consisted of two regions, i.e., central columella or statenchyma and peripheral regions. The columella cells (statocyte) are in the form of oval to rectangular. We also found that all root with marked gravitropism have statoliths that settle along different walls of that statocyte. Caps vary in form and size within root system of A. marina. The most striking feature of the root is the distinct and extensive root cap with quite long files of cells. From its shape, structure, and location, it seems clear that the root caps protects the cells under it from abrasion and assists the root in penetrating the soil.
... Ball and Pidsley, 1995), inundation stress (e.g. Ashford and Allaway, 1995), predation on propagules or seedlings (e.g. Mc-Kee, 1995), pre-dispersal frugivory (e.g. ...
Mangroves grow in an active sedimentary environment and are therefore closely linked to physical coastal processes. Seedlings colonize dynamic tidal flats, after which mangroves have the potential to change their physical environment by attenuating hydrodynamic energy and trapping sediments. Disturbance from hydrodynamic energy of waves or currents and the resulting sediment dynamics appear to be a critical bottleneck for seedling establishment on tidal flats and at the forest fringe. However, knowledge about the mechanisms at the single plant level and the spatial pattern of disturbance is limited. By means of a flume study, we demonstrate that a surface erosion threshold of as little as 1–3 cm depth can lead to failure of young seedlings. By monitoring accretion/erosion for 8 months along cross-shore transects in southwest Thailand, we show that especially on the bare mudflat, the physical sediment disturbance regularly exceed the critical erosion thresholds derived from the flume study. Physical sediment parameters along the same transects were analysed to deduct patterns of hydrodynamic energy attenuation. Grain size analysis and erosion/accretion data showed only limited energy dissipation within the fringing Avicennia/Sonneratia zone, sediment dynamics only dropped below for seedlings lethal values within the denser Rhizophora zone. Overall, present results emphasize that (i) seedling survival is extremely sensitive to physical-driven sediment dynamics and (ii) that such physical disturbances are not only present on the idal flats but can penetrate a significant distance into the forest. Spatio-temporal patterns in sediment dynamics should hence be considered when conducting restoration of mangrove ecosystems.
... Pioneer species have evolved growth form and life-history characteristics to reduce drag force and reduce dislodgment in hydrodynamic environments. Avicennia marina seedling stems are flexible compared to terrestrial tree seedlings, owing to the presence of aerenchyma tissue (Ashford & Allaway, 1995), with foliage predominantly at the tip of the seedling. These adaptations allow for significant stem bending and reduced drag, respectively. ...
Intertidal wetlands such as saltmarshes and mangroves provide numerous important ecological functions, though they are in rapid and global decline. To better conserve and restore these wetland ecosystems, we need an understanding of the fundamental natural bottlenecks and thresholds to their establishment and long-term ecological maintenance. Despite inhabiting similar intertidal positions, the biological traits of these systems differ markedly in structure, phenology, life history, phylogeny and dispersal, suggesting large differences in biophysical interactions. By providing the first systematic comparison between saltmarshes and mangroves, we unravel how the interplay between species-specific life-history traits, biophysical interactions and biogeomorphological feedback processes determine where, when and what wetland can establish, the thresholds to long-term ecosystem stability, and constraints to genetic connectivity between intertidal wetland populations at the landscape level. To understand these process interactions, research into the constraints to wetland development, and biological adaptations to overcome these critical bottlenecks and thresholds requires a truly interdisciplinary approach.
