Habitat suitability of the Wadden Sea for restoration of Zostera marina beds

A conceptual model is proposed, describing potential Zostera marina habitats in the Wadden Sea, based on reported data from laboratory, mesocosm and field studies. Controlling factors in the model are dynamics, degree of desiccation, turbidity, nutrients and salinity. A distinction has been made between a higher and a lower zone of potential habitats, each suitable for different morphotypes of Z. marina. The model relates the decline of Z. marina in the Wadden Sea to increased sediment and water dynamics, turbidity, drainage of sediments (resulting in increased degree of desiccation) and total nutrient loads during the twentieth century. The upper and lower delineation of both the higher and the lower zone of potential Z. marina habitats appear to be determined by one or a combination of several of these factors. Environmental changes in one of these factors will therefore influence the borderlines of the zones. The lower zone of Z. marina will be mainly affected by increased turbidity, sediment dynamics, degree of desiccation during low tide and nutrient load. The higher zone will be affected by increases in water and sediment dynamics, desiccation rates and nutrient loads. Potential Z. marina habitats are located above approx. –0.80 m mean sea level (when turbidity remains at the same level as in the early 1990s) in sheltered, undisturbed locations, and preferably where some freshwater influence is present. At locations with a high, near-marine, salinity, the nutrient load has to be low to allow the growth of Z. marina. The sediment should retain enough water during low tide to keep the plants moist. Our results suggest that the return of Z. marina beds within a reasonable time-scale will require not only suitable habitat conditions, but also revegetation measures, as the changes in the environment resulting from the disappearance of Z. marina may impede its recovery, and the natural import of propagules will be unlikely. Furthermore, the lower zone of Z. marina may require a genotype that is no longer found in the Wadden Sea. Received: 26 April 1999 / Received in revised form: 15 October 1999 / Accepted: 16 October 1999     

Growth and respiration in two mangrove species at a range of salinities

Growth and dark respiration rates were measured in leaves and roots of seedlings of Avicennia marina (Forsk.) Vierh, (grey mangrove), and Aegiceras corniculatum (L.) Blanco (river mangrove). Plants were grown in a soil mixture at ambient temperatures and watered with 0.25 and 100% sea-water. Oxygen uptake was measured in excised root and leaf samples. In both species growth was maximal in 25% sea-water, and root respiration was lowest in 100% sea-water. Differences were found between the two species in the responses of leaf respiration to salinity. In A. corniculatum leaf respiration was raised in both 25 and 100% sea-water, while in A. marina only leaves in 100% sea-water showed higher rates of respiration. These results are consistent with the view that A. marina is the more salt-tolerant of the two species. In A. corniculatum the respiration rates of the hypocotyl were also measured, and were much higher in 100% sea-water than in the other two treatments. The results suggest that at high salinities there is a high metabolic cost in the shoots of both species, and that at such salinities rates of root respiration may be limited by the supply of substrate from the shoots.     

Protection of photosynthetic O2 evolution against heat inactivation: the role of chloride,pH and coupling status

Heat inactivation of photosynthetic O₂ evolution was studied in isolated thylakoids from spinach (Spinacia oleracea) and mangrove (Avicennia marina) leaves. Different temperatures, salt, pH and uncoupler effects were investigated. From these results and others in the literature it was concluced that chloride loss from the membrane and, more specifically, the oxygen-evolving complex of photosystem II, may be the cause of inhibition of oxygen evolution during heat inactivation.Abbreviations Hepes 4-(2-hydroxyethyl)-1-piperazinethanesulfonic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol - Tricine N-2-hydroxy-1, 1-bis (hydroxymethyl) ethyl glycine - EDTA ethylenediaminetetraacetic acid - FeCN K-ferricyanide     

IMMUNOLOCALIZATION OF CENTRIN IN OXYRRHIS MARINA (DINOPHYCEAE)1

A new polyclonal antibody was raised against centrin isolated from the flagellate green alga Spermatozopsis similis (Chlorophyta; anti-SSC). It stains by immunofluorescence and immunoelectron microscopy well-known reference systems for centrin like the nucleus–basal body connectors in Chlamydomonas reinhardtii (Chlorophyta) and the system II fibers (rhizoplasts) of Scherffelia dubia (Chlorophyta). In addition, it recognizes in immunoblots a single 20-kDa protein in isolated cytoskeletons of Spermatozopsis similis and Tetraselmis striata (Chlorophyta) as well as purified centrin isolated from Tetraselmis striata. Using this antibody, centrin was localized in whole cells and isolated cytoskeletons of Oxyrrhis marina Dujardin (Dinophyceae) by immunofluorescence and immunogold electron microscopy. In the flagellar apparatus of O. marina, five different structures were antigenic. Four short fibers (connectives 1–4) link the basal bodies to the four major fibrous flagellar roots, which do not cross-react with anti-centrin. The most prominent of the labeled structures (connective 5), a crescent-shaped fiber, extends from the flagellar canal of the transverse flagellum along the base of the tentacle to the flagellar canal of the longitudinal flagellum, interconnecting the distal parts of the microtubular roots/bands in the basal apparatus. For most of its length, it underlies and is connected to a transversely oriented subamphiesmal microtubular band. In immunoblot analyses, anti-SSC recognizes only a single 20-kDa protein in cytoskeletons of O. marina. Functional and phylogenetic aspects of centrin-containing structures in dinoflagellates are discussed.     

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.     

Sodium and potassium relations of Spergularia marina following N and P deprivation: results of short-term growth studies

In this, we consider the coordination of plant growth and ion acquisition, reporting the short-term adjustments of growth and K⁺ and Na⁺ relations which follow when plants are subject to a sudden deprivation of N and P. The plant used for the experiments, Spergularia marina (L.) Grieseb., is a small coastal halophyte, and the growth medium was 0.2 × modified seawater. By considering nutrients whose availability has not been changed, we report on an aspect of organismal integration which has received little attention either experimentally or in mathematical models. The studies are limited to the first 60 h after N and P deprivation in order to consider changes that, if they are not primary responses, are not temporally remote, passive adjustments. For growth analyses, plants were used approximately 30 days after germination and 16 days after transfer to solution culture. Random harvests were made at hourly invervals, and after 12 h, one-half of the plants were transferred to cultures without N or P. Tissue analyses were used to calculate relative growth rates, relative accumulation rates and net uptake rates. For comparison, isotope uptake studies using ⁴²K⁺ and ²²Na⁺ were conducted at 12, 36 and 60 h after deprivation. The effects on growth and biomass allocation were very rapid, detectable within 13 h. K⁺ transport also responded quickly, and from the beginning of the study, there was essentially no net translocation of K⁺ to the shoot. Isotope studies confirmed the responsiveness, with translocation reduced 33 and 90% after 12 and 36 h, respectively. Though Na⁺ adjustments were slower, they were coordinated with growth such that tissue concentrations in the N and P-deprived plants were comparable to those in the controls. We conclude that N and C are insufficient elements on which to build mathematical models useful to environmental physiologists. At a minimum, the incorporation of K⁺ relations in growth models would both allow the development of the osmotic potential needed to drive cell expansion, and provide a means to probe –experimentally as well as mathematically – the coordinating mechanisms of plant growth and resource management.     

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.     

PHYLOGENETIC AFFINITIES OF THE SARCINOCHRYSIDALES AND CHRYSOMERIDALES (HETEROKONTA) BASED ON ANALYSES OF MOLECULAR AND COMBINED DATA1

Small-subunit ribosomal RNA nucleotide sequences were inferred for Giraudyopsis stellifera Dangeard (Chrysomeridales), as well as for Pulvinaria sp. and Sarcinochrysis marina Geitler (Sarcinochrysidales,). Phylogenetic analyses of the molecular data indicate that the former is weakly related to the Phaeophyceae/Xanthophyceae clade, whereas the latter two have affinities to the Pelagophyceae, and the Sarcinochrysidales sensu stricto is transferred to this class. A recent study proposed that the Pelagophyceae belongs to a larger assemblage of chromophytic species characterized by reduced flagellar apparatuses. Although the flagellar apparatus characterizing the Sarcinochrysidales is reduced relative to the Chysomeridaels and some other chromophytes, it is the most complicated to be associated with “the reduced flagellar apparatus” lineage. Cladistic analyses of a traditional data set (largely ultrastructural features of the flagellar apparatus) and a combined traditional/molecular data set were used to assess the evolutionary trends of reduction in the flagellar apparatus within the heterokont chromophytes.     

江苏省不同种植年限的西/甜瓜农田土壤线虫群落特征

在江苏省主要西/甜瓜产区,采集不同种植年限的西/甜瓜农田土壤,采用线虫形态学的鉴定方法,分析了不同种植年限西/甜瓜农田土壤线虫的数量、群落结构及相关生态指数的变化。结果表明:所有调查样点中,共发现土壤线虫54属,平均682条·100 g^-1干土,其中原杆属线虫、拟丽突属线虫和矮化属线虫在不同种植年限的西/甜瓜农田土壤中均为优势属;随着种植年限的增加,土壤线虫的总数量虽无显著变化,但其中食细菌类线虫和杂食-捕食类线虫数量显著减少,而植物寄生类线虫数量显著增加;植物寄生类线虫中的矮化属、根结属线虫数量不断增加;随着种植年限的增加,土壤线虫的多样性指数(H)、瓦斯乐斯卡指数(WI)、自由生活线虫成熟度指数(MI)显著降低,线虫通道指数(NCR)、植物寄生线虫成熟度指数(PPI)、PPI/MI显著升高,其他指数无显著变化;相关性分析结果显示,土壤线虫数量与土壤pH、速效磷、有效锌和有效硼均呈显著正相关;土壤p H、有机质、全氮、速效钾、有效硼和有效锌对土壤优势属线虫的影响较大;连续种植西/甜瓜会增加土壤植物寄生类线虫数量,进而可能造成西/甜瓜连作障碍的发生;连续种植6~10年,土壤线虫的多样性最低、稳定性最差,土壤环境已趋于恶化。