Evidence for top predator control of a grazing ecosystem

The importance of top predators in controlling ecological processes in large, intact ecosystems is unclear. In grasslands that support abundant ungulates, top–down control by predators may be particularly important, because of the tight biogeochemical linkages of ungulate prey with plants and soil microbes. Here, I examined the effects of the recent reintroduction of the gray wolf Canis lupus on ecosystem processes in Yellowstone National Park, where herds of grazing ungulates previously have been shown to stimulate several processes, including soil net nitrogen (N) mineralization. Rates of ungulate grazing intensity and soil net N mineralization were compared before and after wolf reintroduction in grasslands ranging five‐fold in aboveground production. Grazing intensity and grassland net N mineralization declined after wolf reintroduction, a likely partial function of fewer ungulates; wolf predation has been one of several factors implicated in causing the decline in Yellowstone ungulates. In addition, the spatial pattern of grazing and net N mineralization changed after reintroduction. A shift in the spatial patterns of grazer‐associated processes is consistent with a growing body of work indicating that wolves have changed habitat use patterns of ungulates in Yellowstone National Park. These findings suggest widespread wolf effects on ungulate prey, plants, and microbial activity that have spatially reorganized grassland energy and nutrient dynamics in Yellowstone Park.     

Physiological responses of Sargasso Sea picoplankton to nanomolar nitrate perturbations

A study was conducted in July 1989 at three stations in thenorthern Sargasso Sea, where picoplankton (<1 µm)provided approximately half of the standing crop of chlorophyll.Temporal changes in the position of the nitracline at a singlelocation indicated that the vertical supply of nitrate was notat ‘steady-state’ and phytoplankton distributionstracked the nitracline. Our main experimental objective wasto examine the short-term effects of ecologically significantnitrate perturbations (+20 and +100 nM) on the physiologyof <1 µm communities growing at low (nanomolar)ambient nitrate concentrations. A chemiluminescent nitrate methodwas used to measure the time course (up to 4 h) of nitratedisappearance at in situ irradiance, in parallel with measurementsof photosynthetic ¹⁴CO₂ assimilation. Picoplankton growing at<60 nM nitrate rapidly responded to nanomolar nitratesupplements with luxury consumption and enhanced photosynthesisin proportion to their ambient nitrate environment. Light-saturatedSynechococcus populations from the most nitrate-depleted waters(13 nM) had doubled their cellular rate of photosynthesisafter 4 h, in response to a 20 nM nitrate pulse.     

Biochemical Evidence for Formate Transfer in Syntrophic Propionate-Oxidizing Cocultures of Syntrophobacter fumaroxidans and Methanospirillum hungatei

The hydrogenase and formate dehydrogenase levels in Syntrophobacter fumaroxidans and Methanospirillum hungatei were studied in syntrophic propionate-oxidizing cultures and compared to the levels in axenic cultures of both organisms. Cells grown syntrophically were separated from each other by Percoll gradient centrifugation. In S. fumaroxidans both formate dehydrogenase and hydrogenase levels were highest in cells which were grown syntrophically, while the formate-H₂ lyase activities were comparable under the conditions tested. In M. hungatei the formate dehydrogenase and formate-H₂ lyase levels were highest in cells grown syntrophically, while the hydrogenase levels in syntrophically grown cells were comparable to those in cells grown on formate. Reconstituted syntrophic cultures from axenic cultures immediately resumed syntrophic growth, and the calculated growth rates of these cultures were highest for cells which were inoculated from the axenic S. fumaroxidans cultures that exhibited the highest formate dehydrogenase activities. The results suggest that formate is the preferred electron carrier in syntrophic propionate-oxidizing cocultures of S. fumaroxidans and M. hungatei.     

Growth inhibition of putrefactive anaerobe 3679 caused by stringent-type response induced by protonophoric activity of sorbic acid

The inhibitory effects of potassium sorbate on the bioenergetics, phenylalanine uptake, protein synthesis, and certain aspects of cell regulation were examined in putrefactive anaerobe 3679. Undissociated sorbic acid appeared to act as a protonophore by lowering the intracellular pH and dissipating the proton motive force of the membrane. Sorbate inhibited the uptake of phenylalanine, decreased the rate of protein synthesis, and altered patterns of phosphorylated nucleotide accumulation, resulting in increased intracellular concentrations of GTP, ppGpp, and an unidentified compound (possibly pppGpp). The addition of a noninhibitory amount of tetracycline released the inhibition of growth by sorbate. Based on these results, we concluded that the inhibition of putrefactive anaerobe 3679 by sorbate resulted from a stringent-type regulatory response induced by the protonophoric activity of sorbic acid.     

Evolutionary ecology of aeolian and subterranean habitats in Hawaii

Inhospitable lava flows, high altitude stone deserts and subterranean habitats in the Hawaiian islands are now known to support a considerable variety of endemic arthropod species. Current studies of these organisms are revealing a remarkable range of morphological, behavioral and physiological adaptations to the physically extreme environments they inhabit.     

Analysis of teleost hemoglobin by Adair and Monod-Wyman-Changeux models

Summary The allosteric effects of the erythrocytic nucleoside triphosphates (NTP) and of proton concentrations were investigated by precise measurement of Hb–O₂ equilibria of tench hemoglobin (including extreme, high and low saturation ranges) and analysed in terms of the MWC two state model and the Adair four step oxygenation theory.At low concentrations (NTP/Hb ratio=1.0, and pH>7.3) ATP, GTP and protons decrease Hb–O₂ affinity by increasing the allosteric constantL and reducingK _T, the association constant¹ of the deoxy, tense state of the Hb, without significantly affecting that (K _R) of the oxy state, increasing the free energy of cooperativity (G). High concentrations of these effectors, however, also reduceK _R. The greater sensitivity of the half-saturation O₂ tension (P ₅₀) of the Hb to GTP than to ATP at the same concentration, correlates with greater effects of GTP on bothK _T andK _R. The pH and NTP dependence of the four Adair association constants and the calculated fractional populations of Hb molecules in different stages of oxygenation show that the autochthonous NTP effectors and protons stabilize the T structure and postpone the TR transition basic to cooperativity in fish Hb.The possible implications of the findings for aquatic respiration are discussed.Abbreviations ATP adenosine triphosphate - DPG 2,3-diphosphoglycerate (glycerate-2,3-bisphosphate) - GTP guanosine triphosphate - IHP inositol hexaphosphate - NTP nucleoside triphosphates In this paperK _T andK _R are defined as theassociation equilibrium constants instead of dissociation constants (as originally defined by Monod et al. 1965) to facilitate comparison with the Adair constants     

Influences of exercise-stress and adrenaline upon intra- and extracellular acid-base status,electrolyte composition and respiratory properties of blood in tench (Tinca tinca) at different seasons

Summary Exercise-stress in tench resulted in severe acidoses in both the red cells and the extracellular fluid in vivo. These coincident pH decreases conformed to the in vitro pH_i-pH_e relationship for tench blood in the oxygenated state. The extracellular acidosis was primarily respiratory in winter and metabolic in spring and summer. This was due to more effective buffering of metabolic protons in winter by an elevation in [HCO ₃ ^– ] levels, rather than to differences in the lactic- and carbonic acid loads. A good correspondence was found between buffered metabolic protons and increases in [lactate].There was no evidence for -adrenergic red cell swelling and associated red cell pH changes in tench both after exercise and adrenaline infusion. Arterial O₂ transport was, however, improved in exercise by pronounced increases in .Large increases in plasma potassium concentration and small elevations of chloride and calcium levels occurred in exercise. Hematocrit and blood [Hb] also increased, probably due to an adrenergic release of erythrocytes from the spleen, but these increases were small and appeared unimportant for blood O₂ transport.Seasonal differences were found in exercise-induced changes in [lactate], in the magnitude of electrolyte and changes, as well as in resting values for pH_e, pH_i, [HCO ₃ ^– ], [Cl^–] and [Ca⁺⁺]. The origin and importance of these are discussed.     

Thermodynamic analysis of precisely measured oxygen equilibria of tench (Tinca tinca) hemoglobin and their dependence on ATP and protons

Summary Precise oxygen equilibria including extreme, high and low saturation values were determined for hemoglobin (Hb) from the freshwater teleostTinca tinca at three temperatures, each at two pH levels and in the presence and absence of the erythrocytic cofactor ATP, at twofold molar excess over Hb.Analysis of the data in terms of Adair's successive oxygenation theory shows that in the absence of ATP, each of the four oxygenation steps are exothermic, but that net heat release decreases as pH falls from 8.2 to 7.4. ATP greatly depresses the temperature sensitivity of oxygenation particularly at physiological erythrocytic pH, where endothermic cofactor dissociation finds expression in a reverse temperature sensitivity for binding of the 3^rd oxygen molecule to the tetrameric Hb.Enthalpy (H _i) and entropy (S _i) changes of oxygenation vary with oxygenation step, i, as well as with pH and ATP addition, but the variations of H _i are similar to those of S _i reflecting enthalpy-entropy compensation.The data show that the cooperative effects in tench Hb can be dominated either by entropic or enthalpic contributions, depending on the experimental condition and the oxygenation step.     

Novel stabilization of phenylalanine ammonia-lyase catalyst during bioconversion of trans-cinnamic acid to l-phenylalanine

Summary Production of l-phenylalanine from trans-cinnamic acid using isolate SPA10 cells was reduced to 26% of that observed initially when cells were reacted a second time with fresh substrate mixture. The stability (reuseability) of Phenylalanine Ammonia-Lyase (PAL) containing cells was significantly influenced by both the trans-cinnamate concentration and initial reaction pH. Using 2% t-cinnamate, l-phenylalanine production was 7-fold greater after 3 successive runs at pH 9.0 than at the optimum of pH 10.2. Cells reacted in the presence of 5% t-cinnamate were relatively unstable. Permeabilising agents, such as toluene and xylene, stimulated l-phenylalanine production but also enhanced instability of the catalyst. Several effectors were shown to stimulate the initial rate of the PAL bioconversion, but only sorbitol, alginate, glutaraldehyde, polyethylene glycol and glycerol conferred any significant degree of stability. Sparging of cultures and bioreactors with various gases revealed that oxygen enhanced PAL inactivation, CO₂ had little effect and nitrogen conferred remarkable stability on PAL activity for several weeks in culture medium. The presence of chloride ions (from HCl) and aeration of substrate mixtures resulted in poor reuseability of catalyst. A combination of H₂SO₄ substitution for HCl and N₂-sparging resulted in excellent initial conversions and good catalyst stability at 26°C but less at 30°C. The inclusion of 1.5 M sorbitol in reaction mixtures maintained PAL stability over several successive incubations.