On the production,elemental composition (C,N, P) and distribution of photosynthetic organic matter in the Southern Black Sea

Chemical oceanographic understanding of the southernBlack Sea has been improved by recent measurements ofthe optical transparency, phytoplankton biomass (interms of chlorophyll-a and particulate organic matter)and primary productivity. During the spring-autmunperiod of 1995–1996, light generally penetrated onlyinto the upper 15–40 m, with an attenuation coefficientvarying between 0.125 and 0.350 m^2122;1. The averagechlorophyll-a (Chl-a) concentrations for the euphoticzone ranged from 0.1 to 1.5 μg l^2122;1. Coherentsub-surface Chl-a maxima were formed near the base ofthe euphotic zone only in summer. Production rate variedbetween 247 and 1925 in the spring and between 405 and687 mgC m^2122;2 d^2122;1 in the summer-autumn period.The average POM concentrations in the euphotic zonevaried regionally and seasonally between 3.8 and28.6 μm for POC, 0.5 and 3.1 μm for PON and0.02 and 0.1 μm for PP. Atomic ratios of C/N, C/Pand N/P, derived from the regressions of POM data,ranged between 7.5 and 9.6, 109 and 165, and 11.2 and16.6, respectively. In the suboxic/anoxic interface,the elemental ratios change substantially due to anaccumulation of PP cohering to Fe and Mn oxides. Thechemocline boundaries and the distinct chemicalfeatures of the oxic/anoxic transition layer (the so-called suboxic zone) are all located at specificdensity surfaces; however, they exhibit remarkablespatial and temporal variations both in their positionand in their magnitude, which permit the definition of long-term changes in the biochemical properties of theBlack Sea upper layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal cycle of nitrogen and phytoplankton biomass in a well-mixed coastal system (Eastern English Channel)

The hydrological structure of the French coastal part of the eastern English Channel is strongly linked with tidal regimes and riverine input. Two distinct water masses are separated by a frontal area and drift along the coast in SW–NE direction. These two water masses are well-mixed during the entire year. We studied the seasonal dynamic of nitrogenous nutrients, chlorophyll a and organic particulate carbon and nitrogen at two stations, characteristic of these water masses, during the year 1994. Results show (i) a winter stock of nitrate and ammonium, (ii) a pre-bloom period corresponding to the use of ammonium, (iii) a high bloom period of short duration using nitrate, (iv) a post-bloom period with little phytoplanktonic activity probably limited by nutrients other than nitrogen and (v) an autumnal period of reconstitution of stock. The essential difference between the two stations is the importance of winter stock of nutrients and of bloom chlorophyll a concentration, with the coastal station richer than the offshore one. An assumption about the nitrogen available for new production in this area gives a value of 57% of the winter stock of inorganic nitrogen.     

Nutrients in the shadow-nutrients of substance

While the dietary importance of proteins, essential fatty acids, vitamins and trace elements has been well recognised, the role of shadow nutrients, a class of metabolites, which are biosynthesized in the body and serve vital functions, such as lipoic acid, choline, inositol, taurine and carnitine, has not been adequately appreciated. There are reasons to believe that during infancy and in ageing, biosynthesis of these metabolites may be limited. The objective of this review is to highlight the essentiality of these nutrients and the need for their supplementation in the diets of infants and in elderly people. Provision of shadow nutrients where the necessary biosynthetic machinery might not have developed to full stature or might have slowed down, is a new concept in nutrition which needs attention.     

Mineralization dynamics in fallow dryland wheat plots,Colorado

Summary There was a flush of mineralization in fallow wheat plots in the wet and warm summer of 1982 at Akron, Colorado. Peak mineralization rates and concentrations of N and P coincided with a 2.5-fold increase in protozoan biomass. No-till contained considerably more activity than stubble mulch plots, especially in the surface 2.5 cm and there was more water storage in no-till on all dates. Differential management of agricultural residues and the resultant effects upon the microbial community significantly altered patterns of nutrient cycling.     

Änderungen in der Stickstoffversorgung auf Dauerflächen im Brachland

Summary Starting in 1968 plant succession and nitrogen status in the top soil of an old field was investigated. The soil is a calcareous loam which was sterilized by heating. In the absence of human influence distinct successional stages with characteristic floristical and physiognomical features were observed. During the first six years vegetational development was characterized by competition between therophytes and hemicryptophytes. Agricultural treatments such as annual ploughing (spring, summer) and cutting (autumn) were found to change the trend of the succession.Five years after starting the experiment total nitrogen content in the top soil of the control area had increased slightly, while the ploughed plots persisted in their low values. A comparison of the nitrogen mineralisation between 1970 and 1974 showed decreasing amounts of mineral nitrogen in the later stage (1970: 67 kg N_min/ha/30 weeks; 33 kg N_min/ha/30 weeks). On the other hand, mineral nitrogen supply on the ploughed plots was not significantly different after the five-years-period. It is suggested that in old-field vegetation the external nitrogen cycle of the early therophyte stage changed to an internal one when long-lived hemicryptophytes, rhizome- and root-budding geophytes became dominant.Tables 1 to 4 show the vegetation development under different treatments; the figures represent average cover values per vegetation season using Londo's (1975) scale. Table 5 contains the total nitrogen concentration values in the uppermost of 10 cm of mineral soil, and Table 6 lists the values for soil volume, mean soil temperatures, average water content, and mineral nitrogen supplies for 1970 and 1974.

Contribution to the Symposium of the Working Group for Succession Research on Permanent Plots, held at Yerseke, the Netherlands, October 1975.     

Seasonal succession of planktonic and epiphytic algae in a canal in Southern England

The standing crop of phytoplankton in a canal in southern England remained low during 1973 and 1974, seldom exceeding 5 × 10⁴ cells/1. Since phosphorus, nitrogen and silicon occurred abundantly in the water, competition with higher plants for some other substance must have limited development. Although the standing crop of epiphytic algae associated withNasturtium officinale andGroenlandia densa seemed to be limited by the number of attachment sites, this factor was of little importance in the case of algae attached toCladophora glomerata. Achnanthes minutissima v.cryptocephala was always predominant in the epiphytic assemblages, representing 50–8o% by numbers of the flora. The limited pool of predominant epiphytic taxa may have restricted the communities' ability to adapt to fluctuations in environmental conditions. The grazing of isopods, amphipods and molluscs probably never limited algal densities.     

Total nitrogen and phosphorus balance sheet in a typic ustochrept soil under intensive cropping and fertilizer use

Summary Balance sheets were computed for total nitrogen and phosphorus in plough layer (0–15 cm) of a Typic Ustochrept soil under continuous multiple cropping for seven years (1971–72 to 1977–78) with a fixed rotation of pearl millet (Pennisetum typhoideum L.) wheat (Triticum aestivum L.) (Vigna sinensis Savi.) The treatments considered of soil test-based rates of N, P and K, applied both singly and in combinations together with farm yard manure, sulphur and zinc superimposed over optimum rates (100%) of NPK. Heavy, losses of N (762–899 kg ha⁻¹) occurred in the plots which received high rates of Nviz. 150% of recommended NPK and 100% NPK plus FYM. Application of N alone accelerated N losses whereas addition of P, PK, PKS to N minimised such losses. Enrichment of P (66 to 198 kg ha⁻¹) occurred in all phosphate-treated plots. A marginal net decrease (29–54 kg ha⁻¹) in P levels was observed in control and N alone treatments.     

EFFECTS OF NITRATE CONCENTRATION ON THE GROWTH AND PHYSIOLOGY OF LAMINARIA SACCHARINA (PHAEOPHYTA) IN CULTURE1,2

Laminaria saccharina Lamour. sporophytes were grown in enriched and synthetic media through a range of nitrate concentrations, There was an approximately linear relationship between growth and nutrient concentration up to 10 μ substrate concentration. The half-saturation constant (K_{2) was ca. 1.4 μ NO3-. The internal levels of NO3- increased at substrate concentrations above 10 μM b>3- and reached levels several thousand times higher than the surrounding medium. Thus there is evidence for luxury consumption of NOsb>3}^-. The chlorophyll content and photosynthetic capacities of plants also increased with increasing external NO₃^- The ecological implications of this work are considered.     

Determination of enzyme activities of energy metabolism in the maturing rat oocyte.

Enzyme activities were determined quantitatively in individual rat oocytes to study their energy metabolism during maturation. Low hexokinase activity and high activities of lactate dehydrogenase and enzymes in the phosphate pathway, i.e., glucose 6-P and 6-P gluconate dehydrogenases, were characteristic of immature oocytes. Hexokinase may be a rate-limiting enzyme that enables oocytes to use glucose as an energy source. During maturation, the activities of hexokinase, phosphofructokinase, and malate dehydrogenase increased significantly, suggesting that the glycolytic pathway, as well as the tricarboxylic acid cycle, developed as the first meiotic division proceeded. In contrast, the activities of glucose 6-P and 6-P gluconate dehydrogenases decreased in maturing oocytes. The observation that the enzyme pattern in mature oocytes resembles more closely that in somatic cells appears to be significant, especially in light of previous studies showing this developmental trend in preimplantation embryos.     

The influence of light and nutrient addition upon the sediment chemistry of iron in an arctic lake

The geochemical response of sediments to increased nutrient input to an Alaskan, arctic lake was examined using direct measurements of sediment-water chemical fluxes. An unexpected increase in Fe flux occurred when sediments were exposed to high incident radiation and nutrient concentrations. Correlation between light and acid-soluble Fe concentrations suggests that photoreduction of Fe(III) oxides may occur, but nutrient addition enhanced the effect indicating that primary productivity was also important. The processes controlling the flux of Fe from sediments in this lake were complex and included the redox potential (dissolved oxygen concentration) of the water, quality of organic matter present in the sediment, light, and nutrients supplied from the sediments and/or water column. These four factors together with the possibility of direct uptake of Fe by phytoplankton and the possible release of algal reductants may contribute to Fe cycling in this lake.