Routine metabolism of juvenile spot, Leiostomus xanthums (Lacépède), as a function of temperature, salinity and weight

Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums , were measured over a range of temperatures, salinities and fish weights. As predicted, Q O₂ increased with temperature and decreased with body weight. However, Q O₂ decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log₁₀ Q O₂ (mg O₂ g⁻¹ h⁻¹) = 0.129 log_lo salinity (%0) + 1.604 log₁₀ temperature (°C)-0.1401og₁₀(g)-2.767.     

MACROALGAE SURVIVE DIGESTION BY FISHES1

Small individuals (<15 cm long) of the clingfish Sicyases sanguineus consume as many as 18 seaweed species in Central Chile. Enteromorpha sp. was the only species able to survive digestion by fish recently collected from the field. Enteromorpha compressa and Gelidium chilense also survived by tissue regeneration when offered as food in the laboratory, but only E. compressa showed stimulation of swarmer production. In general, our results on a vertebrate species reproduce previous findings on diverse invertebrate species. Since fish are highly motile, their capacity to disperse algal species by defecation might be of great ecological importance.     

Effect of salinisation of soil on growth and macro- and micro-nutrient accumulation in seedlings of Acacia catechu (Mimosaceae)

The effects of salinisation of soil on Acacia catechu (Mimosaceae) were studied by means of emergence and growth of seedlings and pattern of mineral accumulation. A mixture of chlorides and sulphates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.1, 6.3, 8.2,10.1 and 12.2 dSm⁻¹. A negative relationship between proportion of seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.1 dSm⁻¹. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.1 dSm⁻¹, which suggests that this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. Among the tissues, young roots and stem were most tolerant to salt stress and were followed by old roots and leaves, successively. Leaf tissue exhibited maximum reduction in dry mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated “fine root turnover”, is of importance to the mechanisms of salt tolerance. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K was affected in response to salinity; it rapidly decreased in root tissues with increased salinisation. Nitrogen content decreased in all tissues (leaf, stem and root) in response to low water treatment and salinisation of soil. Phosphorus content significantly decreased, while Ca increased in leaves as soil salinity increased. Changes in tissue and whole plant accumulation patterns of the other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species during salinisation, are discussed.     

Factors influencing the effectiveness of an attracticide formulation against the Oriental fruit moth, Grapholita molesta

An attracticide formulation, LastCall?OFM, was tested against the Oriental fruit moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae) in replicated small plot field trials in apple, Malus domestica (Borkhausen), orchards in South‐eastern Pennsylvania, USA. Attracticide treatments were applied using a calibrated hand pump, and treated plots were compared to similar untreated plots. Male moth activity was monitored using virgin female‐baited traps, and the potential for reduction in mating activity was assessed using sentinel virgin females. A comparison of application rates showed that 1500 droplets per ha of the attracticide formulation was as effective as 3000 droplets per ha, and both application rates reduced captures in synthetic pheromone‐baited traps for prolonged periods. Droplets placed either at high or low positions within the canopy significantly reduced trap capture and mating with sentinel females. In addition, the only sentinel females that mated in the treated plots were located in the untreated portion of the tree canopy. Mate finding behaviour was equally disrupted by formulations with and without insecticide. Therefore, under the test conditions, the mechanism by which the attracticide formulation worked was by disruption of male orientation, and not by the removal of males due to insecticide poisoning. Two field cage experiments tested the impact of population density on the competitiveness of the attracticide formulation compared to virgin females. A significant proportion of males were captured in female‐baited traps at the highest female‐to‐droplet ratio tested. Equal proportions of males were captured in attracticide‐baited traps at male moth densities of 10, 20, 40, and 80 males per cage. These results clarify some of the factors influencing the effectiveness and possible mechanisms of an attracticide management tactic against the Oriental fruit moth.     

Summer Epidemics of Apple Scab: The Relationship between Measurements and their Implications for the Development of Predictive Models and Threshold Levels under Different Disease Control Regimes

A 2‐year study on epidemic progress of apple scab was conducted at Randwijk, the Netherlands, in 1998 and 1999. The summer epidemic caused by conidia was studied instead of the well‐described spring season epidemic originating from ascospores. The aim was to investigate relationships between disease measurements, i.e. disease incidence and severity measures of apple scab, and their implications for the development of predictive models and threshold levels. The study characterized good relationships between the measurements on cultivar Jonagold using regression analyses in three disease control regimes (untreated, organic and integrated). For fruit quality prediction, the relationship between fruit incidence (I_f) and leaf incidence (I_l) in the organic control regime was given by I_f = 1.966 + 0.402 × (I_l) (R² = 0.92). As a result of low level of disease in the integrated control regime, shoot incidence (I_s), with higher values than leaf incidence, was better suited for prediction. The relationship was given by I_f = ?0.162 + 0.028 × (I_s) (R² = 0.91). For the integrated control regime, disease threshold levels were constructed for timing of the final fungicide application. If an apple grower wants to keep fruit infection under 1% incidence (harvest scab threshold), the timing of the final fungicide application (action threshold) should correspond to 4% shoot scab incidence at the beginning of August. The results are compared with similar studies and their biological interpretation is discussed.     

Soil-surface carbon dioxide efflux and microbial biomass in relation to tree density 13 years after a stand replacing fire in a lodgepole pine ecosystem

The effects of fire on soil‐surface carbon dioxide (CO₂) efflux, F_S, and microbial biomass carbon, C_mic, were studied in a wildland setting by examining 13‐year‐old postfire stands of lodgepole pine differing in tree density (< 500 to > 500 000 trees ha^?1) in Yellowstone National Park (YNP). In addition, young stands were compared to mature lodgepole pine stands (～110‐year‐old) in order to estimate ecosystem recovery 13 years after a stand replacing fire. Growing season F_S increased with tree density in young stands (1.0 µmol CO₂ m^?2 s^?1 in low‐density stands, 1.8 µmol CO₂ m^?2 s^?1 in moderate‐density stands and 2.1 µmol CO₂ m^?2 s^?1 in high‐density stands) and with stand age (2.7 µmol CO₂ m^?2 s^?1 in mature stands). Microbial biomass carbon in young stands did not differ with tree density and ranged from 0.2 to 0.5 mg C g^?1 dry soil over the growing season; C_mic was significantly greater in mature stands (0.5–0.8 mg C g^?1 dry soil). Soil‐surface CO₂ efflux in young stands was correlated with biotic variables (above‐ground, below‐ground and microbial biomass), but not with abiotic variables (litter and mineral soil C and N content, bulk density and soil texture). Microbial biomass carbon was correlated with below‐ground plant biomass and not with soil carbon and nitrogen, indicating that plant activity controls not only root respiration, but C_mic pools and overall F_S rates as well. These findings support recent studies that have demonstrated the prevailing importance of plants in controlling rates of F_S and suggest that decomposition of older, recalcitrant soil C pools in this ecosystem is relatively unimportant 13 years after a stand replacing fire. Our results also indicate that realistic predictions and modeling of terrestrial C cycling must account for the variability in tree density and stand age that exists across the landscape as a result of natural disturbances.     

ESTIMATING PUP PRODUCTION OF HARP SEALS, PAGOPHILUS GROENLANDICUS, IN THE NORTHWEST ATLANTIC

Photographic and visual aerial surveys to determine current pup production of Northwest Atlantic harp seals were conducted off Newfoundland and in the Gulf of St. Lawrence during March 1999-Photographic surveys were conducted on all whelping concentrations between 14 and 24 March, whereas a visual survey was made of the southern Gulf concentrations on 14 March. Pup production was estimated to be 739,100 (SE = 96,300, CV = 13.0%) at the Front, 82,600 (SE = 22,500, CV = 27.2%) in the northern Gulf, and 176,200 (SE = 25,400, CV = 14.4%) in the southern Gulf (Magdalen Island) for a total of 997,900 (SE = 102,100, 10.2%). Changes in aerial survey estimates indicate that pup production has increased since 1994. A new method to correct for the temporal change in the proportion of pups present on the ice was examined by fitting the percentage of pups observed in three age-dependent stages to a Normal distribution. The results were compared to those obtained from a more complex model used previously. The Simple model produced slightly higher, and hence more conservative, estimates of the proportion of births that had occurred before the time of the survey than the Complex model. When using the Simple model fewer assumptions regarding the start date of pupping and the proportion of older pups remaining on the ice were required, the herd had to be followed for a shorter period, and a more convenient means of calculating confidence limits was available.     

STRUCTURE AND REPRODUCTION OF AMANSIA AND MELANAMANSIA GEN. NOV. (RHODOPHYTA,RHODOMELACEAE) ON THE SOUTHEASTERN AFRICAN COAST1

Four species of Amansia Lamouroux were initially found in Natal. More Complete studies on these species revealed a new genus, Melanamansia, Which is described on the basis of presence of two dorsal pseudopericentral cells in two new species from Natal (M. seagriefii sp. nov. & M. fimbrifolia sp. nov.) in addition to other structural characters and features of pigmentation and reproduction. Pseudopericentral cells are not present in the type species of Amansia, A. multifida Lamouroux. The other two species of Amansia occurring in Natal, A. glomerata C. Agardh & A. loriformis sp. nov., have characters similar to the type species. Comparison of species from other regions of the world has shown that eight additional species, previously assigned to Amansia, belong to the new genus.     

Penicillin acylase-catalyzed synthesis of β-lactam antibiotics in water-methanol mixtures: effect of cosolvent content and chemical nature of substrate on reaction rates and yields

The synthesis of four β-lactam antibiotics (penicillin G, pivaloyloxymethyl ester of penicillin G, ampicillin and pivampicillin) catalyzed byEscherichia coli penicillin acylase has been investigated in water-methanol mixtures. The enzyme reactions were either thermodynamically or kinetically controlled at the same conditions using phenylacetic acid andd--phenylglycine methyl ester as acyl donors and 6-aminopenicillanic acid and pivaloyloxymethyl 6-aminopenicillanic acid as acyl acceptors. It has been found that the influences of the cosolvent content on the reaction rates and synthetic yields are significantly different depending on the substrates used in the experiments. On the other hand, within certain ranges of the methanol content (up to ca. 40% (v/v) the residual activities of the enzymes in water-methanol mixtures were only slightly lower than those in aqueous media. To analyze the factors that determine the reaction rate in water-cosolvent mixtures, the effect of methanol on the apparent pK values of the substrates has been investigated, and a mathematical model has been developed on the basis of the assumption that the enzyme binds non-ionized substrates. Model simulation results indicate that the solvent effect on reaction rates is mainly attributed to the kinetic effects of changes in apparent pK values.     

Root productivity in a lowland tropical rain forest in Mexico

Fine root productivity was estimated in a lowland tropical rain forest at Los Tuxtlas (SE Mexico) and examined in relation to climatic factors. Two root diameter classes were defined (class I,<1 mm; class II, 1–3 mm). Total root productivity was estimated to 1.95 t ha^–1 year^–1, a value which is lower than those reported from other rain forest sites. Significant differences in root dry weight were found among months and between diameter classes throughout the year. Class I monthly means formed two groups: one corresponding to the months of highest precipitation, and the other to the relatively dry season. Class II monthly means also formed two groups, although these were unrelated to the regional precipitation pattern. A multiplicative regression model of productivity on precipitation was significant for both root classes when rainfall data of the previous month were used, while a linear regression model was significant only for class I roots when temperature data of two months before were used; these results suggest a delay in the effect of climatic conditions on root productivity. While the seasonal pattern of root productivity is clearly related to the annual rainfall distribution, the low total annual productivity may be related to the very high soil fertility at Los Tuxtlas.