Photosynthetic pathways and the ecological distribution of the chenopodiaceae in Isreal

Summary Fifty-four species of the Chenopodiaceae in Israel were examined for their anatomical features, ¹³C values, habitat and phytogeographical distribution. 17 species have ¹³C values between -20 and -30and non-Kranz anatomy (NK) and are therefore considered as C₃ plants. 37 species have ¹³C values between -10 and -18 and Kranz or C₄-Suaeda type anatomy and are therefore considered as C₄ plants. Some C₄ plants have leaf structure which seems to be intermediate between the Kranz and the C₄-Suaeda type of leaf anatomy.The segregation of the species into photosynthetic groups shows tribal and phytogeographical grouping. Most of the C₃ Chenopods are either mesoruderal plants or coastal halophytes, with a distribution area which covers the Euro-Siberian as well as the Mediterranean phytogeographical regions. The C₄ Chenopods are mainly desert or steppe xerohalophytes with a distribution area which includes the Saharo-Arabian and/or Irano-Turanian phytogeographical regions.     

On the possible role of organic melanoidin polymers as matrices for prebiotic activity

Summary One of the major diagenetic pathways of organic matter in recent sediments involves the condensation of cellular constituents, particularly amino acids and sugars, into insoluble melanoidin-type polymers. These polymers consist mainly of humic and fulvic acids and make up the major part of the organic carbon reservoir in recent sediments. We suggest that a similar set of reactions between abiotically formed amino acids and sugars, and more generally between aldehydes and amines, occurred on a large scale in the prebiotic hydrosphere. The rapid formation of this insoluble polymeric material would have removed the bulk of the dissolved organic carbon from the primitive oceans and would thus have prevented the formation of an "organic soup".Melanoidin polymers have several properties which make them attractive hypothetical precursors of contemporary oxidation-reduction coenzymes: 1. they contain heterocyclic nitrogen compounds similar to the nitrogenous bases; 2. they contain a high concentration of stable free radicals; and 3. they tend to concentrate those heavy metals which play prominent roles in contemporary enzymic redox processes. The prebiotic formation of similar polymers could, therefore, have provided the starting point for a basic class of biochemical reactions.We suggest that the prebiotic scenario involved chemical and protoenzymic reactions at the sediment-ocean interface in relatively shallow waters and under conditions not much different from those of the recent environment.On leave from the Isotope Department, Weizmann Institute of Sciences, Rehovot, Israel. This is the address for reprint requests.On leave from the Department of Cell and Molecular Biology, San Francisco State University, San Francisco, California.On leave from the Department of Biophysics, University of Houston, Houston, Texas.     

The microbiology and biogeochemistry of the Dead Sea

The Dead Sea is a hypersaline water body. Its total dissolved salts content is on the average 322.6 gm/liter. The dominant cation is Mg (40.7 gm/liter), followed by Na (39.2 gm/liter), Ca (17 gm/liter) and K (7 gm/liter). The major anion is Cl (212 gm/liter), followed by Br (5 gm/liter); SO₄ and HCO₃, are very minor. The lake contains a limited variety of microorganisms and no higher organisms. The number of recorded species is very low, but the total biomass is reasonably high (about 10⁵ bacteria/ml and 10⁴ algal cells/ml). The indigenous flora is comprised mainly of obligate halophylic bacteria, such as the pink, pleomorphicHalobacterium sp., aSarcina-like coccus, and the facultative halophilic green alga,Dunaliella. Sulfate reducers can be isolated from bottom sediments. Recently a unique obligate magnesiophile bacteria was isolated from Dead Sea sediment. Several of the Dead Sea organisms possess unusual properties. TheHalobacterium sp. has extremely high intercellular K⁺ concentration (up to 4.8M) and extraordinary specificity for K⁺ over Na. TheDunaliella has very high intracellular concentration of glycerol (up to 2.1M). The microorganisms exert marked influence on some biogeochemical processes occurring in the lake, such as the control of the sulfur cycle and the formation and diagenesis of organic matter in the sediments. The Dead Sea is an excellent example of the development of two different mechanisms for adjusting to a hostile environment. The algae adjust to the high salinity by developing a mechanism for the exclusion of salts from the intracellular fluid and using glycerol for osmotic regulation. On the other hand, the bacteria adapt to the environment by adjusting their internal inorganic ionic strength, but not composition, to that of the medium. The problem of population dynamics and limiting factors for algal and bacterial productivity are discussed in view of the total absence of zooplankton and other consumers other than bacteria.     

The Dead Sea — an economic resource for 10 000 years

The archaeological and historical record of the Dead Sea as an economic resource is longer than that of any other hypersaline lake. Although it is completely devoid of life, except for a few bacteria and algae, the climatic and geological conditions in the Dead Sea basin have produced circumstances which made this lake important for the economy of the area. The salt which was produced by evaporation of the water, or by quarrying from the salt diapir of Mt. Sodom, on the Dead Sea coast, is referred to in the Bible and in the Talmud. It was harvested until the 1930's. Potash has been extracted from the brine, by solar processes, since 1931 and today the Dead Sea is a major source of potash and bromine. The asphalt, which is found in seepages along the shores and in large blocks, occasionally found floating on the lake, has been used by the inhabitants of the area for waterproofing baskets and for decorative purpose, since the Pre-ceramic Neolithic Period, 10 000 years ago. Later, the asphalt became a major export item to Egypt. During the Early Bronze age, 4000 years ago, it was used mostly to glue flint implements to wooden handles and in the Graeco-Roman period it was used as one of the components in the embalming of Egyptian mummies. The area around the Dead Sea was the only source of balsam, perhaps the most important incense and medication of the Ancient World. Remains of a 7th century B.C. perfume factory, were found in Ein Gedi. During later periods, until the Arab conquest in the 7th century A.D., the growing of balsam was an imperial monopoly. The area of the Dead Sea was famous, for over 2000 years, for its dates and sugar. The therapeutical and medicinal properties of Dead Sea water and the hypersaline hot springs on its shore, were famous throughout the Ancient World. For example, King Herod the Great, 2000 years ago, used to visit the area to cure his many diseases. This practice continues today, and the lakes has become a major center for treatment of psoriasis. There is pictorial, archaeological and historical evidence to support the Dead Sea's importance as a trade artery for over 2300 years.     

Effect of water regime on carbon isotope composition of lichens

δ¹³C values of the lichens Ramalina duriaei and Teloschistes villosus collected in their natural habitat were repeatedly measured during 2 years. Results show variations in the stable carbon isotope ratios (¹³C/¹²C). Such variations are correlated to the seasonal rainfall, i.e. low values of δ¹³C of the lichens during the winter and high values of δ¹³C during the dry summer. Relatively low δ¹³C values were obtained also in laboratory experiments with lichens grown under controlled humid conditions and in lichens collected from humid habitats.     

Assessing changes to ecosystem structure and function following invasion by Spartina alterniflora and Phragmites australis: a meta-analysis

Biological invasions resulting from anthropogenic activities are one of the greatest threats to maintaining ecosystem functioning and native biodiversity. Invasions are especially problematic when the invading species behaves as an ecosystem engineer that is capable of transforming ecosystem structure, function, and community dynamics. Of particular concern is the spread of emergent wetland grasses whose root systems alter hydrology and structural stability of soils, modify ecosystem functions, and change community dynamics and species richness. To address the threats posed to ecosystems across the globe, management practices focus on the control and removal of invasive grasses. However, it remains unclear how severely invasive grasses alter ecosystem functions and whether alterations persist after invasive grass removal, limiting our ability to determine if management practices are truly sufficient to fully restore ecosystems. Here, we conducted a meta-analysis to quantify ecological alterations and the efficacy of management following the invasion of Spartina alterniflora and Phragmites australis, two common and pervasive invaders in coastal wetlands. Our results indicate that S. alterniflora and P. australis significantly alter measures of ecosystem functioning and organismal abundance. Invaded ecosystems had significant elevations in abiotic carbon and nitrogen fixation and uptake in areas with invasive grasses, with differential photosynthetic pathways of these two grass species further explaining carbon fluxes. Moreover, evidence from our analyses indicates that management practices may not adequately promote recovery from invasion, but more data are needed to fully assess management efficacy. We call for future studies to conduct pairwise comparisons between uninvaded, invaded, and managed systems and provide research priorities.

     

Nutrients in pore waters from Dead Sea sediments

Pore waters were separated from 50 cm-long cores of Dead Sea sediments raised from waters depths of 25, 30 and 318 m. The salinity of the pore water is close to that of the overlying water at 225–230 g l^–1 chloride. The titration alkalinity of the pore water is about 60 % of the overlying water, and sulfate is also depleted. Ammonia and phosphate concentrations are higher than those of the water column with up to 50 mg l^–1 N-NH₃ (ten times increase) and 350 µg l^–1 P-PO _inf4 ^sup3– (four to eight times increase). Early diagenetic reactions are a result of decomposition of organic matter and of water-sediment interactions, resulting in aragonite precipitation, phosphate removal to the sediments, probably by absorption on iron-oxyhydroxides followed by remobilization, reduction of sulfate and formation of iron sulfides and accumulation of ammonia. Mass balance calculations show that pore water contribute about 80% of the ammonia and 30% of the phosphate input into the Dead Sea water column. On the other hand, the sediments act as a sink for carbonate and sulfate.     

Scavenging of soluble organic matter from the prebiotic oceans.

The existence of hot or cold "nutrient broth" or "primeval soup" is challenged on the basis of the recent geochemistry of soluble organic carbon in the oceans. Most of the dissolved organic carbon is recycled quickly by organisms, but the residual, biologically refractive, organic matter is efficiently scavenged from the oceans (residence time of 1000 to 3500 years) by nonbiologically mediated chemical and physical processes, such as adsorption on sinking minerals, polymerization and aggregation to humic type polymers or by aggregation to particulate matter through bubbling and sinking of this material to the ocean bottom. Since there is no reason to believe that such nonbiological scavenging was not operative in the prebiotic oceans as well, then the prolonged existence of "organic soup" is very doubtful. The question of the origin of life is thus assumed to be related to solid-liquid interfacial activity, and the answer may be associated with sediment-water interaction rather than with solution chemistry.     

Behind the discovery of "Nissenbaum's fixative"

The author describes the serendipitous discovery, conception, development, and history of Nissenbaum's Fixative while an undergraduate biology major in the early 1950s. The subsequent uses, applications, and modifications over the past forty-seven years are also described. Some of the modifications omitted from his short original paper are mentioned. Highlights of his subsequent career in the field of medicine are noted.     

Scavenging of soluble organic matter from the prebiotic oceans

The existence of hot or cold nutrient broth or primeval soup is challenged on the basis of the recent geochemistry of soluble organic carbon in the oceans. Most of the dissolved organic carbon is recycled quickly by organisms, but the residual, biologically refractive, organic matter is efficiently scavenged from the oceans (residence time of 1000 to 3500 years) by nonbiologically mediated chemical and physical processes, such as adsorption on sinking minerals, polymerization and aggregation to humic type polymers or by aggregation to particulate matter through bubbling ans sinking of this material to the ocean bottom. Since there is no reason to believe that such nonbiological scavenging was not operative in the prebiotic oceans as well, then the prolonged existence of organic soup is very doubtful. The question of the orgin of life is thus assumed to be related to solid-liquid interfacial activity, and the answer may be associated with sediment-water interaction rather than with solution chemistry.