A New Stromatolitic Mat Builder Discovered from Late Precambrian in Northern China

Abundant and preserved chain algal microfossils have been discovered in cherty stromatolitic mats from the second member of Gaoyuzhuang Formation (about 1,500 Ma old), Ling-qiu county of Shanxi province, China. They are described as Veteronostocale moniliforme Xu et Gao sp. nov.. The small diametral trichomes resemble the Family Nostocaceae in possessing specilized cells resembling the classic heterocysts and akinetes. This paper gives emphasis to the following remark: (1) The Gaoyuzhuang stromatolitic mats were products of microbial (Veteronostocale moniliforme) activity and the plant Nostocaceae was one of the main stromatolitic builders as both modern and Precambrian stromatolite-forming microorganisms; (2) Based on the fact that the chain fossils are preserved perpendicularly to the laminations the rates of sedimentation and algal growth were probably equal and each small sedimentary rhythm could be completed in about one or two months; (3) According to the environment and habits of living Nostoc Precambrian hydrosphere might be of a fresh water type.     

Dispersal and recruitment of a canopy-forming intertidal alga: the relative roles of propagule availability and post-settlement processes

The daily settlement of eggs and zygotes of the monoecious brown alga Pelvetia compressa (J. Agardh) De Toni was measured on artificial substrata in areas inside and outside patches of adults in the high intertidal zone of central California. Settlement was generally 1–2 orders of magnitude higher under the adult canopy. This pattern seems to be due to the synchronous release of gametes during the daytime low tide. The release of gametes also appears periodic over longer time scales (e.g., 3- and 14-day cycles). In spite of the high availability of propagules under the adult canopy, juveniles were most abundant outside patches, where propagule availability was lower. In both areas, juveniles were disproportionately associated with patches of a red algal turf [primarily Endocladia muricata (Postels & Ruprecht) J. Agardh and Masticarpus papillata (C. Agardh) Kützing]. The turf, which is less common under the P. compressa canopy, may offer protection from dislodgment, grazing, and/or desiccation and thus facilitate recruitment at this site. Overall, post-settlement processes appear more important in determining population structure than does the availability of propagules in areas in and around patches of adults. However, the apparent small range of dispersal of P. compressa may make propagule availability an important limitation to the establishment of new populations and may restrict gene flow between populations. Received: 31 October 1997 / Accepted: 31 August 1998     

5-Aminolevulinic acid production by Chlorella sp. during heterotrophic cultivation in the dark

5-Aminolevulinic acid (ALA) was produced aerobically in the dark during growth on glucose by a newly isolated Chlorella sp. When levulinic acid (20 mM), a competitive inhibitor of ALA dehydratase, was added repeatedly to the medium, about 1.5 mM of ALA was produced extracellularly. Glutamate (30 mM) added with levulinic acid (20 mM, given repeatedly) enhanced ALA production up to 1.9 mM, indicating that ALA might be synthesized via the C-5 pathway.K. Sasaki was with the Hiroshima-Denki Institute of Technology, 6-20-1, Nakano, Akiku, Hiroshima, 739-03, Japan; and is now with the Department of Biotechnology. The University of New South Wales, Sydney, NSW, 2052, Australia; K. Watanabe, T. Tanaka and Y. Hotta are with the Cosmo Research Institute, 1134-2, Gongendo, Satte, Saitama, 340-01, Japan. S. Nagai is with the Department of Fermentation Technology, Faculty of Engineering, Hiroshima University, 4-1, Kagamiyama 1 chome, Higashi-Hiroshima, 724. Japan.     

Germination and Photosynthetic Responses to Salinity and Alkalinity in <i>Avicenna marina</i> Propagules

Avicenna marina (Forssk.) Vierh is a halophytic mangrove. The reproductive unit is green and has photosynthetic propagules. Mangroves are naturally exposed to fluctuations in some abiotic factors at the soil surface, including salinity and alkalinity. The objective of this study was to determine the effects of two salts including NaCl and NaHCO₃ on germination processes and discuss the relationships between cotyledon photosynthesis and embryo axis growth in A. marina propagules. These propagules came from Al Birk, located on the shoreline of the Saudi Red Sea. The results showed that the studied salts did not affect neither the final germination percentage nor the embryo axis growth. However, rooting and root growth were delayed by both salts at 300 mM and were strongly inhibited by 600 mM NaHCO₃. Both NaCl and NaHCO₃ reduced the photosynthetic activity. These two salts did not affect the other photosynthetic parameters, including stomatal conductance, net transpiration, and intercellular CO₂. Thereafter, the reduction in net photosynthesis was not related to any limitation of stomatal conductance. The early germination phase was independent of cotyledon photosynthesis, whereas rooting and root growth may be limited by reduced photosynthesis under NaCl and NaHCO₃.     

The Role of Propagule Banks from Drainage Ditches Dominated by Free‐Floating or Submerged Plants in Vegetation Restoration

Dominance by free‐floating plants results in a loss of plant species in many waters. An important source for re‐establishment of non‐floating aquatic plants can be the propagule bank. This study focuses on whether the propagule bank of free‐floating plant–dominated ditch sediments can serve as potential source for recovery of a diverse plant community. The first objective was to determine differences in propagule germination from sediments of ditches in the Netherlands that differ in vegetation composition through a seedling‐emergence experiment. The second objective was to analyze the effect of sediment disturbance on the number of germinating propagules. The results show that, compared to sediments from ditches with submerged vegetation, sediments from free‐floating plant–dominated ditches produced significantly lower numbers of individuals and species of submerged and emergent plants, while numbers of individuals and species of free‐floating plants were higher. These results suggest that sediments from free‐floating plant–dominated ditches have lower potential to recover a diverse plant community probably resulting from positive feedback mechanisms caused by the vegetation present, maintaining the free‐floating plant–dominated state. Sediment disturbance strongly favors the germination of free‐floating plant propagules, especially from free‐floating plant–dominated ditch sediments. Ditch maintenance activities such as mowing and dredging will therefore likely favor persistence of the free‐floating plant–dominated state. To shift from dominance by free‐floating plants to a more diverse plant community, alternative maintenance methods should be considered that cause less sediment disturbance together with measures that promote colonization such as temporary drawdown or re‐introduction of species.     

Seed dispersal by waterbirds in southern Africa: comparing the roles of ectozoochory and endozoochory

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