bluuebunny/crossref_metadata_2025_split huggingface dataset:
On-Farm Testing of the pnutGRO Crop Growth Model in Florida1
Authors: Gilbert R. A. , Boote K. J. , Bennett J. M. 
Published: April 2010

Abstract
pnutGRO is a peanut crop growth simulation model which calculates crop carbon, nitrogen and water balances at the process level. An on-farm evaluation of pnutGRO v1.02 was conducted at 15 field sites in two Florida counties during the 1990 and 1991 cropping seasons. Independent crop and soil data sets were collected to evaluate pnutGRO simulations. The accuracy of the pnutGRO simulations was affected by year and location. Sites where peanut (Arachis hypogaea L.) was grown in rotations following bahiagrass (Paspalum notatum Fleuge) (Levy County, 1990) had low disease pressure, high pod yields (5260 kg/ha), and the best model fit (pnutGRO simulations were within 9% of observed yield data). Sites where peanut followed other row crops often showed high infestation levels of root-knot nematode [Meloidogyne arenaria (Neal) Chitwood] or stem rot (Sclerotium rolfsii Sacc.) (Jackson County, 1991). This resulted in reduced pod yields (3260 kg/ha) and poorer model fit (pnutGRO simulations were 44% above observed yields). pnutGRO correctly predicted relative yield decreases due to drought. Overall, pnutGRO v1.02 appears to be most useful as a predictor of optimal peanut yield for specific cultivars under given soil and weather conditions. Inclusion of pest and disease damage functions would improve model accuracy for farms where biotic stress reduces potential peanut yield.
A method for determining exoproteolytic activity in natural waters
Authors: Somville Martine , Billen Gilles 
Published: April 2010

A very sensitive method allowing determination of exoproteolytic activity in natural water is based on the use of aminoacyl‐β‐naphthylamide, which gives rise to a fluorescent product upon hydrolysis of its peptidelike bond by filtered or unfiltered water samples. Specificity of the method to exoproteases is demonstrated by a strong competitive inhibition effect of added proteins.A good correlation is found between exoproteolytic activity and the rate of amino acid utilization by microheterotrophs in various aquatic environments.
Factors influencing Diaptomus distributions: An experimental study in subtropical Florida1
Authors: Elmore J. L. 
Published: April 2010

In central and southern Florida Diaptomus dorsalis is the sole diaptomid in most eutrophic lakes whereas Diaptomus floridanus and Diaptomus mississippiensis co‐occur in oligotrophic and mesotrophic lakes. The importance of food availability and water quality in determining the species distributions of Diaptomus was ascertained by culturing the three species in water from a lake of each type with its natural phytoplankton present and with the natural phytoplankton removed and Chlamydomonas added at a concentration above feeding saturation.The experimental evidence indicated that neither food availability nor water quality is important in excluding D. floridanus and D. mississippiensis from the eutrophic lakes. Additional data suggested that strong predation pressure may prevent these two species from occupying lakes of this type. However, low food availability seemed of major importance in excluding D. dorsalis from the oligotrophic and mesotrophic lakes. Competition is likely because food levels are always limiting and a potential competitor is present in the form of D. floridanus—in the same subgenus and close to the same size. Additional evidence suggests that predation is probably of lesser importance to the zooplankton in lakes of these types.
Methodological problems in the simultaneous assessment of photosynthesis and nutrient uptake in phytoplankton as functions of light intensity and cell size
Authors: Nalewajko C. , Garside C. 
Published: April 2010

The processes of nitrate, ammonia, and phosphate uptake in marine phytoplankton differed in the extent of dependence on light. Phosphate uptake in the 3–8‐µm size class, but not in the whole population, showed a saturation‐type relationship to light. Biomass‐specific photosynthesis and nutrient uptake rates were highest in the smallest, 0.2–3‐µm, size class, and decreased in the 3–8‐µm, and in the >8‐µm classes.C:N:P uptake ratios at ambient light were different in the 0.2–3‐µm, 3–8‐µm, and >8‐µm size classes. In the whole population, uptake ratios at ambient light differed from ratios based on light‐optimized data. However, the measurements are subject to many problems which preclude an assessment of the accuracy of the ratios.
The trophic role of colonial Radiolaria in oligotrophic oceanic environments1,2
Authors: Swanberg Neil R. 
Published: April 2010

Five species of colonial Radiolaria collected by divers on 27 cruises were used for experimental metabolic measurements. Carbon content as an indicator of colony size correlated well with cell number in three species, with approximately 50, 100, and 200 ng C per cell. Chlorophyll a per radiolarian cell (from symbiotic dinoflagellates) varied widely between colonies and could not be predicted from colony size by better than a factor of 2. Photosynthetic carbon incorporation at high levels of natural light ranged from 10 to 76 pmol C · cell−1 · h−1. Mean respiration in two species was 5.3–5.5 µl O2 · mg C−1 · h−1. Respiration is probably balanced by photosynthesis under normal light conditions.Colonial Radiolaria were present at 92% of 268 oceanic stations and very abundant at 34%. Measured abundances ranged from 0.04 to 14 colonies · m−3 in the water column and reached 540 colonies · m−3 in patches at the surface. Because the primary productivity of their symbionts is probably consumed in maintenance metabolism, colonial Radiolaria may be most important to the epipelagic oligotrophic ecosystem as gelatinous predators.
Carboxylating enzyme activity and photosynthetic end products of phytoplankton in the shallow and deep chlorophyll layers of Castle Lake1
Authors: Priscu John C. , Goldman Charles R. 
Published: April 2010

The patterns of carbon assimilation of the Castle Lake phytoplankton were measured under various environmental conditions. The flow of carbon into polysaccharides and lipids plus low molecular weight metabolites was generally highest at low temperatures and low light (i.e, under‐ice and deep‐water populations). Enrichment with nitrogen to nitrogen‐deficient algae did not significantly alter the patterns of carbon assimilation during time‐series experiments. However, the relative rates of polysaccharide and protein synthesis were increased when the entire epilimnion of the lake was fertilized with nitrogen.On the average about 15% more carbon could potentially be fixed by the anaplerotic enzyme phosphoenolpyruvate carboxylase (PEPCase) than the Calvin Cycle enzyme ribulose‐1,5‐biphosphate carboxylase (RuBPCase). The parameter, RuBPCase : PEPCase/photon saturated in vivo photosynthesis (Pmax), was consistently >1.0 liter ·h‒1·µg‒1 C and showed significant differences between the 3‐m and 20‐m algal populations, indicating that they may be physiologically distinct with respect to carbon metabolism.The proportion of 14C incorporated into protein increased as the ratio of RuBPCase to PEPCase increased. The converse was true for the relative synthesis of lipid + low molecular weight (LMW) compounds while the proportion of 14C incorporated into polysaccharide varied little with RuBPCase : PEPCase. These findings and others from the literature do not corroborate existing simple biochemical models for this relationship, implying that other carboxylating enzymes may be important in the carbon metabolism of certain algae.
Porewater evidence for a dynamic sedimentary iron cycle in salt marshes1
Authors: Giblin Anne E. , Howarth Robert W. 
Published: April 2010

Dynamic transformations of iron occur seasonally at Great Sippewissett Marsh, Massachusetts. Small changes in the dissolved iron concentration in porewater represent only a small fraction of the iron involved in transformation reactions during the year. During the growing season, salt marsh grasses oxidize the sediment, and a large percentage of sedimentary pyrite is converted to an oxidized iron mineral. Over the fall and winter there is a net increase in pyrite as the grass is anaerobically decomposed.When oxidation rates in summer are high enough to neutralize the alkalinity produced by sulfate reduction and substantially lower the pH, oxidized iron minerals become increasingly soluble and iron levels in the porewater increase. If large amounts of soluble iron are lost by tidal flushing, iron availability may limit pyrite formation in later years. Sulfide concentrations in the porewater would then increase, leading to depressed growth of Spartina alterniflora.For most of the year the porewaters of Great Sippewissett were undersaturated with respect to all iron monosulfide minerals and supersaturated with respect to pyrite (FeS2). Thus pyrite formation at Great Sippewissett probably occurs directly by reaction of polysulfides with iron and not by reactions of FeS with elemental sulfur. Porewaters were always undersaturated with respect to manganese minerals. Porewaters taken from marshes at Sapelo Island, Georgia, in fall were supersaturated with respect to pyrite at all depths and appear to be saturated for iron monosulfides below 12 cm at all sites.
Effects of flow rate on fluorescence in vivo during continuous measurements on Gulf of Mexico surface water1
Authors: Sweet Stephen T. , Guinasso Norman L. 
Published: April 2010

The intensity of in vivo fluorescence changed with the rate of sample flow during continuous measurements made in the Gulf of Mexico. Most previous measurements have indicated no relationship between fluorescence intensity and sample flow rate.The effect was not observed at flow rates between 0 and 250 cm3·min‒1; however, above 500 cm3·min‒1 fluorescence increased promptly when flow rate increased. Residence time of sample in the illuminated zone of the fluorometer ranged from 0.29 s (at 1,500 cm3·min‒1) to 1.7 s (at 250 cm3·min‒1). This flow rate effect implies that phytoplankton fluoresce with an intensity which varies as a function of illumination time. The Kautsky induction effect may provide an explanation for the observed variation.
Combined autoradiography and immunofluorescence for estimation of single cell activity by ammonium‐oxidizing bacteria1,2
Authors: Ward B. B. 
Published: April 2010

Immunofluorescence and 14CO2 autoradiography were used for simultaneously enumerating and assaying the autotrophic activity of ammonium‐oxidizing bacteria in seawater. Relative activity (14CO2 assimilation as measured by autoradiography) and abundance were measured in simulated in situ incubations at seven stations in the primary NO2‒ maximum region of the Northeast Pacific Ocean. More than 104 cells· liter were present; relative activity often showed a peak near the surface and an increase in the NO2‒ max region below the photic zone. The method permits assessment of individual cell activity; most cells at all depths were active in CO2 assimilation, usually at low and quite variable levels. There were no differences in relative activity between samples incubated under simulated in situ conditions and in the dark.Relative activity was positively correlated with the abundance of ammonium‐oxidizing bacteria, temperature, total dark CO2 assimilation (as measured by liquid scintillation counting of replicate samples), and pheopigment concentration, and negatively correlated with oxygen concentration.
Temporal and spatial variability of phytoplankton in a subtropical ecosystem1,2
Authors: Bienfang P. K. , Szyper J. P. , Okamoto M. Y. , Noda E. K. 
Published: April 2010

Phytoplankton conditions were examined at two stations off the leeward coast of Oahu, Hawaii. Significant temporal variability was observed in the chlorophyll and pheopigment data. Significant temporal and spatial variability was observed in the ATP and productivity data. Most (60–80%) of the microbial biomass occurred in the <3‐µm fraction. Pigment profiles showed distinct subsurface maxima at 90 m. Annual primary production was estimated at 60.4 g C·m‒2·yr‒1, and low nutrient levels and P:B ratios indicated persistent nutrient limitation.Dissimilar inflection depths for nitrate, phosphate, and silicate indicated nitrate availability and phosphate limitation in the lower photic zone. Production between January and May was 11 × that between May and November; productivity below 44 m accounted for most of this variation. Biological and physical analyses indicate that variations in vertical nutrient supply, related to differences in current shear, caused this temporal variation.
Radium in the Dead Sea: A possible tracer for the duration of meromixis1
Authors: Stiller M. , Chung Y. C. 
Published: April 2010

Three profiles of 226Ra in the meromictic Dead Sea measured during 1963–1978 indicate that the radium activities in the upper water mass were higher than in the lower water mass. All three profiles indicate a similar radium inventory. The Jordan inflow is not the primary source of radium to the Dead Sea. Mineral springs and submerged seepages are probably more important contributors.The age of the meromictic structure is estimated by a model which requires that the radium inventory of the lake be at a steady state, that sometime in the past the radium profile of the lake had been uniform (when either the lake was monomictic or an overturn had ended an earlier meromictic phase) and that the contemporaneous profiles of radium have been built up by inflows of radium solely into the upper water mass, while the monimolimnion is relict, isolated, and loses radium only by radioactive decay. Supporting evidence is presented suggesting that the above conditions may be fulfilled. Thus, it is possible to estimate that the Dead Sea was meromictic for about 300 years before the turnover in 1979.From tentative balances of the Dead Sea dissolved salts it is shown that a previous overturn might have occurred at a lower lake level than in 1979.
The long and short term feeding condition in field‐caught Calanus pacificus, as determined from the lipid content
Authors: Hakanson John L. 
Published: April 2010

The wax ester and triglyceride contents of Calanus pacificus were measured as indices of feeding condition. The copepod was reared to copepodite V on 100, 300, and 900 µg C·liter‒1 of the diatom Thalassiosira weissflogii and also subjected to changing food concentrations at the fifth copepodite stage. The resulting lipid content was measured. The naupliar stages did not appear to benefit from a food concentration higher than 100 µg C·liter‒1 although there was an increasing difference in wax ester content after C III among the three food concentrations. The triglyceride content seemed a good indicator of recent feeding, being completely lost after 3 days of starvation. The wax ester content was a good indicator of feeding over a period of a week.Field samples were collected on six occasions off San Diego, in summer 1982 and spring 1983. At five of the six stations the field‐caught animals were very well fed, having a much higher wax ester content than at 300 µg C·liter‒1 of T. weissflogii in the laboratory. On one occasion the wax ester and triglyceride contents indicated that the field population was more poorly fed. The variability in lipid content was measured at each station.Data are shown to suggest that quality of food is very important and that Chl a or particulate carbon are poor indicators of food for late stage C. pacificus.
A nitrogen‐15 isotope dilution study of ammonium production and consumption in a marsh sediment1
Authors: Bowden William B. 
Published: April 2010

Gross rates of ammonium production and consumption by microbes were estimated from isotope dilution of extractable 15NH4+ in surface sediment samples from a tidal freshwater marsh in Massachusetts. At 13°C gross ammonium production was 11.6 ± 2.9 nmol N · (cm3 fresh sediment)−1 · h−1. This rate equaled or exceeded gross ammonium consumption in the absence of plant root uptake [6.4 ± 4.0 nmol N ·( cm3 fresh sediment)−1 · h−1] so that ammonium accumulated linearly for 50–70 h in the sediment samples [5.2 ± 1.6 nmol N · (cm3 fresh sediment)−1 ·h−1]. In the field, this excess ammonium is presumably available for plant uptake. Ammonium production and consumption rates were highest in surface sediments and fell rapidly with depth. Temperature has a strong influence on both rates (Q10 = 2.6). Substrate quality and availability, both of which generally decrease with sediment age or depth, are probably more important than end‐product inhibition as rate‐controlling factors in these sediments. In particular, the relationship between ammonium production and consumption rates at different depths and sediment ligin content is clearer than between these rates and dry weight or ash‐free dry weight sediment.The annual, net rate of ammonium production in the top 10 cm of unmixed, surface sediments was estimated from short term ammonium accumulation rates to be about 1.7 mol N · m−2. However, net ammonium production severely overestimated the true turnover time of ammonium as estimated by isotope dilution (5 days). Most important, while isotope dilution of ammonium is a good indicator of ammonium turnover rates, it may be a poor indicator of total nitrogen turnover in sediments (and so of total microbial activity) because it is insensitive to the nitrogen that microbes assimilate directly from the solid substrates to which they adhere.
Needlelike projectiles observed issuing from lysing Trichodesmium (Cyanophyta) cells1
Authors: Borstad Gary A. , Borstad Lorraine E. 
Published: April 2010

During cell lysis of the filamentouscyanophyte Trichodesmium (=Oscillatoria), some cells (5–12 µm) produce 60‐µm‐long needlelike projectiles that exit the cells at rates up to 50 µm · s−1. We can offer no explanation for this previously unreported phenomenon but feel that it may be related to the fragility of the organism and the difficulty of culturing it.
Tritiated thymidine incorporation and the growth of heterotrophic bacteria in warm core rings1
Authors: Ducklow Hugh W. , Hill Suzanne M. 
Published: April 2010

The time‐course of the incorporation rate of [methyl‐3H]thymidine ([3H]TdR) was established during 6–12‐h incubations of natural bacterial populations sampled from the surface layers of warm core Gulf Stream rings. Parallel estimates of changes in cell numbers were made in order to examine the relationships between TdR incorporation and population growth for oceanic bacterial populations. Our results indicate that a conversion factor of 4 × 1018 cells produced per mole of [3H]TdR incorporated yielded estimates of bacterial production which were within a factor of 2 or 3 of production estimates derived from changes in cell numbers in seawater cultures. We observed a significant, direct relationship between the initial rates of TdR incorporation per cell and specific growth rates and conclude that initial short term (15–45 min) assays of TdR incorporation are a valuable tool for studying bacterial production in oceanic waters.In most incubations, the rate of TdR incorporation increased more rapidly than did cell numbers. Analyses of the time‐courses of TdR incorporation rates yielded estimates of specific growth rates for the actively dividing bacteria ranging from 0.08 to 0.51 h−1. Very large conversion factor values were derived from these data. The discrepancy between “growth” determined from TdR incorporation rates and total bacterial numbers in seawater cultures has not been observed in previous studies of coastal, estuarine, or lacustrine bacteria, but was a consistent feature of our studies on oceanic populations. We suggest that this may reflect the opportunistic character of oligotrophic bacteria. Rapid enhancement of TdR incorporation may indicate the capability of oligotrophs to grow rapidly when favorable conditions arise.
The life cycle and productivity of the amphipod Gammarus mucronatus on a northern Massachusetts salt marsh
Authors: LaFrance Katherine , Ruber Ernest 
Published: April 2010

Gammarus mucronatus was the dominant amphipod found in the salt marsh pools of the Parker River National Wildlife Refuge. Densities were positively and highly associated with the presence of floating algal mat dominated by Cladophora spp.Gammarus mucronatus is multivoltine with some overlap of cohorts. The first juveniles appeared in April, first adults matured in May at 3.5–4.5‐mm length (77% mature at 4.5 mm). Individuals from the last cohort, which began in November, matured at larger sizes (15% at 4.5 mm, 100% at 6.5 mm). The equation of egg number (N) against length of female (L) was N = 9.00L – 36.31 for overwintered females and N = 3.05L – 3.38 for the smaller summer females. Egg production was equivalent to 2.5 kcal m−2 yr−1.The mean cohort interval was 112 days and mean cohort turnover rate (P : B) was 4.3. The two midsummer cohorts had the lowest growth efficiencies, 0.34 and 0.37. The first cohort, spanning 77 days (21 April–9 July), contributed the highest daily rates, more than half the annual production (8.7 g m−2), and the highest growth efficiency, 0.56. Several approaches to the calculation of annual production yielded a range of 12.4–15.8 g m−2 yr−1 dry wt with turnover rates also from 12.4 to 15.8.Mean annual production was equivalent to 64.1 and respiration to 67.0 kcal m−2. When coupled with egg production this gave a mean growth efficiency of 0.50. When the values for respiration, growth, and reproduction are summed, the energy flow through G. mucronatus is equivalent to 5.8% of the net annual primary production in these pools.
Sulfur constituents and cycling in waters, seston, and sediments of an oligotrophic lake
Authors: David Mark B. , Mitchell Myron J. 
Published: April 2010

Organic and inorganic sulfur constituents in streams, the water column, seston, and sediments of an oligotrophic Adirondack lake were measured for 2 years (1981–1983). Soluble organic S constituents (C‐bonded S and ester sulfate) were 1–18% of total S in streams, the water column, and lake outlet. Seston S (0.3–1.2% dry mass) in South Lake consisted of ester sulfate (44–59%), C‐bonded S (32–43%), sulfate (10–16%), and nonsulfate inorganic S (<2%). Rates of S deposition measured in sediment traps were highest after spring turnover. The organic matter content (52– 81% dry mass) of traps at 5, 8, and 15.5 m showed no significant differences.Net mineralization of seston inputs was 26% based on mass balance calculations, with 43% of the ester sulfate input mineralized. Because most of the S input to the sediments was not mineralized, organic S accumulated and constituted the major (74% of total S) S component of the sediment.
Vertical flux and biogeochemical turnover regulate nutrient limitation of net organic production in the North Pacific Gyre
Authors: Smith S. V. , Kimmerer W. J. , Walsh T. W. 
Published: April 2010

Water samples collected at a station in the North Pacific Gyre near Hawaii precisely define the temporal average vertical profile of dissolved inorganic and organic N and P (DON and DOP). DON and DOP concentrations decrease with depth. As shown by other studies, the regression of NO3− (with or without NH4−) vs. PO43− yields an approximately Redfield slope and a negative nitrogen intercept. If DON and DOP are included in the regression equation, the intercept approaches 0.Vertical flux ratios of dissolved materials are calculated with a one‐dimensional diffusion model. Downward mixing of DON offsets about 6% of the upward NO3− flux; downward DOP mixing offsets only about 4% of the upward PO43− flux. Net production of particulate organic matter in the euphotic zone is N limited because of slow biochemical turnover of dissolved organic N relative to that of dissolved organic P and to downward mixing.