Minimum Turnover Research Articles

Temporal Dynamics of Scout Release-Behavior of Termitophagous Ponerine ant, Megaponera Analis

AbstractMegaponera analis is an obligate termitophagous species endemic to sub-Saharan Africa. The species forages by sending out scouts to search for termites. Once termites are located, the scouts return to the nest and recruit nest mates. Scouts face unpredictable environmental conditions, including sudden flooding, temperature changes, high winds and predation by natural enemies. We observed 519 scouting trips from 18 different colonies over three years to determine how long it takes for the colony to replace a scout that has likely died while on scouting duty or is lost due to environmental perturbations. Study areas were at Maremani, Musina, Masebe and D’nyala Nature Reserves in the Limpopo Province of South Africa. We introduced definitions of scouting turnover, scouting trip, and scouting session. Scouting turnover is the time it takes a successive scout to leave the nest for a trip, whereas a scouting trip is the journey a scout takes from the nest in search of food. Since M. analis shows bimodal foraging behavior, the morning observations were recorded as the first scouting session, while the subsequent session, which starts in the afternoon, was recorded as the second scouting session. The mean scouting turnover for all 519 trips was 9.36 ± 0.64 (SD) minutes. When turnover was divided into sessions, the first scouting session lasted a mean of 7.77 ± 12.17 (SD) minutes, while the second had 10.34 ± 18.32 (SD) minutes. The minimum turnover was zero minutes, and the maximum was 124 minutes.

Developing an Entrepreneurial Spirit: Case Study of Entrepreneurial Vocational School Students in Jombang

This research investigates the phenomenon of students who are active in entrepreneurship, explaining the motivations behind their involvement, the obstacles they face, as well as the development of emerging aspects of entrepreneurship and ways to improve them. Qualitative methods with a case study approach were used in this research. Data were analyzed through reduction, display and inference, with triangulation to ensure validity. Respondents consisted of students who had been running a business for at least 1 year, with a minimum turnover of 2 million per month, and were actively involved as owners in business development. Research findings show that students' main motivation for entrepreneurship is earning income for living and tuition fees, optimizing time, and the desire to strengthen themselves and contribute to society. In addition, aspects of entrepreneurship that develop include leadership, independent work, hard work, collaboration, creativity, innovation, as well as courage in making decisions and facing risks.

ANALYSIS OF DEBT SHORT TERM AND RECEIVABLE TURNOVER ON THE PROFITABILITY OF MANUFACTURING COMPANIES

ABSTRACTBased on the survey results for the last 3 years, data on food companies and the minimum turnover of accounts receivable and debt has increased and this has an impact on taking profits in the form of assets. These things can have an impact on the investment invested in shareholders. The purpose of this study is to assess the effect of short-term debt and accounts receivable turnover on asset returns. The samples in this study were 8 companies in the 2015-2019 period. The results of t-test analysis partially show that short-term debt does not have a significant effect on profitability, receivables turnover has a significant effect on profitability. Keywords: short-term debt, accounts receivable turnover, profitability

Canopy management practices in mulberry: impact on fine and coarse roots

Canopy management practices viz. lopping, pruning, coppicing and pollarding in trees alter branch density, height, leaf area index and rooting pattern of the trees. The present study was conducted to quantify the impact of canopy management practices and intercropping on fine and coarse roots distribution in mulberry (Morus alba). In total, six treatments comprising of three management practices (pollarding, coppicing and lopping) and two cropping situations (intercropping and without intercropping) were evaluated. Vertical and lateral distribution of fine root biomass (FRB) was recorded through sequential core method in different seasons. Coarse root distribution and biomass was studied using excavation method. Results revealed that canopy management treatments viz., coppicing and pollarding reduced the FRB as compared to lopping treatment in both intercropped and non-intercropped situation. Results also revealed that majority of the fine root biomass (67.3%) was confined in 0–15 cm soil layer. All the canopy management treatments under non-intercropped plots showed higher production rate as compared to intercropped plots. Fine root turnover rate (yr−1) was highest (0.592) in lopping treatment in non-intercropped plots whereas, the minimum turnover rate was recorded in coppicing treatment (0.331) in non-intercropped plots. Coarse root biomass was highest in case of intercropped plots in all the three canopy management treatments. Pollarding + turmeric cultivation showed the maximum root biomass followed by lopping + turmeric intercropping treatment. The main and primary roots in all the treatments accounted for > 70% biomass except for coppicng + turmeric treatment, whereas secondary and tertiary roots contributed about 40% biomass. All the treatments showed a pronounced decrease in root biomass with increasing soil depth and 75–84% of the total root biomass (main + lateral roots) was allocated in the top 30 cm of the soil profile. From the study, it can be concluded that tree management practices have direct impact on fine and coarse root distribution and should be judiciously used for avoiding competition in intercropping situation.

N‐Hydroxyphthalimide Anchored on Diamond Nanoparticles as a Selective Heterogeneous Metal‐free Oxidation Catalyst of Benzylic Hydrocarbons and Cyclic Alkenes by Molecular O2

AbstractN‐hydroxyphthalimide (NHPI) derived from trimellitic anhydride has been covalently anchored (4 wt %) through ester bonds to the surface of commercial diamond nanoparticles previously functionalized by chemical and thermal treatments (DH). IR spectroscopy of the NHPI/DH solid shows the presence of a characteristic peak at 1735 cm−1 attributable to the ester bond, while solid‐state MAS 13C NMR spectroscopy shows two broad bands corresponding to carbon atoms of carbonyl groups (167 ppm) and aromatic carbons (127 ppm). NHPI/DH promotes autoxidation of isobutylbenzene involving superoxide (O2.−) and hydroperoxide (HOO⋅) radicals; NHPI/DH can be reused at least three times and reach a minimum turnover number as high as 20 600, which is probably due to the inertness of the diamond surface, allowing free diffusion of reactive oxygen species. Analogous materials in which NHPI was anchored on activated carbon and multiwall carbon nanotubes were inefficient as autoxidation catalysts. NHPI/DH is able to promote also selective aerobic oxidation of other benzylic hydrocarbons and cycloalkenes.

Spectral Trends of Solar Bursts at Sub-THz Frequencies

Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 – 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 – 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

Biofilm scrubbing for restoration—algae community composition and succession in artificial streams

Photoautotrophic biofilms play a pivotal role in self-purification of rivers. We took advantage of the biofilm’s cleaning capacity by applying artificial stream mesocosms, called algae turf scrubberTM (ATS), to reduce the nutrient load of a highly eutrophicated backwater in Vienna (Austria). Since purification strongly depends on benthic algae on the ATS, we focused on the algae community composition and succession. Estimation of coverage, photographic documentation for micromapping, species identification and pigment analyses were carried out. Already one week after exposition, 20–30 different taxa were recorded, suggesting a rapid colonization of the substrate. In total around 200 taxa were identified, mainly belonging to Chlorophyta, Bacillariophyceae and Cyanoprokaryota. Nonmetric multidimensional scaling implied that season and succession strongly influenced species composition on the ATS and a minimum turnover of 0.28 indicates a development towards a more stable community at the end of experiments. We measured maximum biomass production of ~250 g m−2 in June and August and during a period of 5 months nearly 19 kg ha−1 phosphorus could be removed. ATS systems proved to retain nutrients and produce algae biomass in an environmentally friendly and cost effective way and thus support restoration of highly eutrophicated water bodies.

Minimum Turnover Analysis in Turkish Tourism Sector

The main purpose of this study is to detect and analyze the minimum turnover in Turkish tourism sector regarding sociodemographic, professional, business and geography specialties of the workers. The ratio of the sum of the staff who changes only once in a year in one position in one business and the total number of the staff who work during the same period is expressed with minimum turnover rate and a new perspective is introduced to the literature. In the study, data belonging to a total of 5764 wageworkers who work at lodging companies, travel agencies and tour operators with food and beveragefirms are used. Data are imported from the data set of 2011 Household Labor Survey (HLS) from Turkish Statistical Institute and are subjected to Cross-tabs, Chi-Square, Annova and T-test analysis by SPSS software program. It is found that there are significantdifferences between turnover rate and sociodemographic, professional, business and geographical characteristics.

Prometheus’s heart: what lies beneath

A heart attack kills off many cells in the heart. Parts of the heart become thin and fail to contract properly following the replacement of lost cells by scar tissue. However, the notion that the same adult cardiomyocytes beat throughout the lifespan of the organ and organism, without the need for a minimum turnover, gives way to a fascinating investigations. Since the late 1800s, scientists and cardiologists wanted to demonstrate that the cardiomyocytes cannot be generated after the perinatal period in human beings. This curiosity has been passed down in subsequent years and has motivated more and more accurate studies in an attempt to exclude the presence of renewed cardiomyocytes in the tissue bordering the ischaemic area, and then to confirm the dogma of the heart as terminally differentiated organ. Conversely, peri-lesional mitosis of cardiomyocytes were discovered initially by light microscopy and subsequently confirmed by more sophisticated technologies. Controversial evidence of mechanisms underlying myocardial regeneration has shown that adult cardiomyocytes are renewed through a slow turnover, even in the absence of damage. This turnover is ensured by the activation of rare clusters of progenitor cells interspersed among the cardiac cells functionally mature. Cardiac progenitor cells continuously interact with each other, with the cells circulating in the vessels of the coronary microcirculation and myocardial cells in auto-/paracrine manner. Much remains to be understood; however, the limited functional recovery in human beings after myocardial injury clearly demonstrates weak regenerative potential of cardiomyocytes and encourages the development of new approaches to stimulate this process.

Decadal changes in climate and ecosystems in the North Atlantic Ocean and adjacent seas

Climate change is unambiguous and its effects are clearly detected in all functional units of the Earth system. This study presents new analyses of sea-surface temperature changes and show that climate change is affecting ecosystems of the North Atlantic. Changes are seen from phytoplankton to zooplankton to fish and are modifying the dominance of species and the structure, the diversity and the functioning of marine ecosystems. Changes also range from phenological to biogeographical shifts and have involved in some regions of the Atlantic abrupt ecosystem shifts. These alterations reflect a response of pelagic ecosystems to a warmer temperature regime. Mechanisms are complex because they are nonlinear exhibiting tipping points and varying in space and time. Sensitivity of organisms to temperature changes is high, implicating that a small temperature modification can have sustained ecosystem effects. Implications of these changes for biogeochemical cycles are discussed. Two observed changes detected in the North Sea that could have opposite effects on carbon cycle are discussed. Increase in phytoplankton, as inferred from the phytoplankton colour index derived from the Continuous Plankton Recorder (CPR) survey, has been detected in the North Sea. This pattern has been accompanied by a reduction in the abundance of the herbivorous species Calanus finmarchicus. This might have reduced the grazing pressure and increase diatomaceous ‘fluff’, therefore carbon export in the North Sea. Therefore, it could be argued that the biological carbon pump might increase in this region with sea warming. In the meantime, however, the mean size of organisms (calanoid copepods) has dropped. Such changes have implications for the turnover time of biogenic carbon in plankton organisms and the mean residence time of particulate carbon they produce. The system characterising the warmer period is more based on recycling and less on export. The increase in the minimum turnover time indicates an increase in the ecosystem metabolism, which can be considered as a response of the pelagic ecosystems to climate warming. This phenomenon could reduce carbon export. These two opposite patterns of change are examples of the diversity of mechanisms and pathways the ecosystems may exhibit with climate change. Oversimplification of current biogeochemical models, often due to lack of data and biological understanding, could lead to wrong projection on the direction ecosystems and therefore some biogeochemical cycles might take in a warmer world.

Origin and turnover of ECM proteins from the inner limiting membrane and vitreous body

The inner limiting membrane (ILM) and the vitreous body (VB) are two major extracellular matrix (ECM) structures that are essential for early eye development. The ILM is considered to be the basement membrane of the retinal neuroepithelium, yet in situ hybridization and chick/quail transplant experiments in organ-cultured eyes showed that all components critical for ILM assembly, such as laminin or collagen IV, are not synthesized by the retina. Rather, ILM proteins, with the exception of agrin, originate from the lens or (and) ciliary body and are shed into the vitreous. The VB serves as a reservoir providing high concentrations of ILM proteins for the instant assembly of new ILM during rapid embryonic eye growth. The function of the retina in ILM assembly is to provide the cellular receptor proteins for the binding of the ILM proteins from the vitreous. The VB is a gelatinous ECM structure that fills the vitreous cavity of the eye. Its major structural proteins, collagen II and fibrillin, originate primarily from the ciliary body. Reverse transcription-PCR and western blotting show that the rate of synthesis of structural, monomeric ILM and VB proteins, such as laminin, collagen IV and II is very high during embryogenesis and very low in the adult. The downregulation of ILM and VB protein synthesis occurs during early postnatal life, and both ILM and VB are from then on maintained throughout life with minimum turnover. Our data explain why ILM and VB do not regenerate after vitrectomy and ILM peeling.

Embryonic Synthesis of the Inner Limiting Membrane and Vitreous Body

The inner limiting membrane (ILM) and the vitreous body (VB) are major parts of the extracellular matrix of the eye. The present study was undertaken to investigate the synthesis and turnover of the ILM and VB in chick and human embryonic and postembryonic eye development. The abundance of ILM and VB proteins was determined by Western blot analysis using samples from chick and human VB of different ages. The mRNA expression of the ILM proteins in lens was determined by in situ hybridization and RT-PCR. Based on the abundance of mRNA expression, the prominent sources of ILM and VB proteins in chick eyes are the lens and ciliary body. In chick, ILM and VB matrix proteins were most abundant in embryonic VB, and their concentration declined precipitously after hatching. Most ILM and VB proteins were no longer detectable in the adult VB. In humans, a similar developmentally regulated expression of ILM and VB proteins in VB was detected: The highest concentrations of ILM and VB proteins were detected in fetal VB, the lowest in the adult VB. The decline in ILM and VB protein synthesis occurred within the first 2 years of life. The abundance of ILM and VB proteins in the embryonic VB, their sharp decline at postembryonic stages, and their very low abundance in the adult VB show that ILM and VB are assembled during embryogenesis and are maintained throughout life with minimum turnover.

Direct experimental evidence for alternative stable states: a review

A large number of studies have presented empirical arguments for the existence of alternative stable states (ASS) in a wide range of ecological systems. However, most of these studies have used non‐manipulative, indirect methods, which findings remain open for alternative explanations. Here, we review the direct evidence for ASS resulting from manipulation experiments. We distinguish four conclusive experimental approaches which test for predictions made by the hysteresis effect: (1) discontinuity in the response to an environmental driving parameter, (2) lack of recovery potential after a perturbation, (3) divergence due to different initial conditions and (4) random divergence. Based on an extensive literature search we found 35 corresponding experiments. We assessed the ecological stability of the reported contrasting states using the minimum turnover of individuals in terms of life span and classified the studies according to 4 categories: (1) experimental system, (2) habitat type, (3) involved organisms and (4) theoretical framework. 13 experiments have directly demonstrated the existence of alternative stable states while 8 showed the absence of ASS in other cases. 14 experiments did not fulfil the requirements of a conclusive test, mostly because they applied a too short time scale. We found a bias towards laboratory experiments compared to field experiments in demonstrating bistability. There was no clear pattern of the distribution of ASS over categories. The absence of ASS in 38% of the tested systems indicates that ASS are just one possibility of how ecological systems can behave. The relevance of the concept of ASS for natural systems is discussed, in particular under consideration of the observed laboratory bias, perturbation frequency and variable environments. It is argued, that even for a permanently transient system, alternative attractors may still be of relevance.

Photooxygenation in Polystyrene Beads with Covalently and Non‐Covalently Bound Tetraarylporphyrin Sensitizers

AbstractTwo reaction protocols are described which involve the use of polymer supports as reaction media for photooxygenation processes: 1) The use of polystyrene beads (PS) loaded with tetraphenyl‐ (TPP) or tetratolylporphyrin (TTP), swollen with the substrate in an appropriate organic solvent and subsequent irradiation under air. Products were isolated simply by dissolution in alcoholic solvents and filtration. 2) Covalently linked tetrastyrylporphyrin in polystyrene‐divinylbenzene beads were synthesized by emulsifier‐free emulsion polymerization and directly used for the photooxygenation protocol described above. The latter alternative allows also the use of less polar solvents for the extraction of the oxygenation products from the polymer beads. From the sensitizer loading degree, an optimal substrate/sensitizer molar ratio of 1,000–2,000 was determined and recyclization is possible for at least five times resulting in a minimum turnover number (with respect to the sensitizer TTP) of 5×104 (after five cycles). Both approaches were applied to the ene reaction of singlet oxygen with citronellol (1), the regioisomeric pinenes 3 and 5, and the allylic alcohols 9a–c, respectively, as well as to the [4+2]‐cycloadditions of singlet oxygen to sorbinol (7) and the chiral diene 11.

δ 13C values of soil organic matter in semiarid grassland with mesquite ( Prosopis) encroachment in southeastern Arizona

Over the past century, C3 woody plants and trees have increased in abundance in many semiarid ecosystems, displacing native C4 grasses. Livestock grazing, climatic fluctuations, and fire suppression are several reasons proposed for this shift. Soil carbon isotopic signatures are an ideal technique to evaluate carbon turnover rates in such ecosystems. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established on homogeneous granitic alluvium to investigate the effects of fire frequency on δ 13C values in surface soil organic matter (SOM). These ranges have had no livestock grazing for 50 years and a well-documented history of fires. Prosopis velutina Woot. (mesquite) trees have altered SOM δ 13C pools by the concentration of plant nutrients and the addition of isotopically light litter. These soil carbon changes do not extend beyond canopy margins. Elevated total organic carbon (TOC), plant nutrient (N and P) concentrations, and depleted SOM δ 13C values are associated with C3 Prosopis on an unburned plot, which enables recognition of former Prosopis-occupied sites on plots with recent fire histories. Elevated nutrient concentrations associated with former Prosopis are retained in SOM for many decades. Surface SOM δ 13C values indicate the estimated minimum turnover time of C4-derived carbon beneath large mature Prosopis is about 100–300 years. In contrast, complete turnover of original C3 carbon to C4 carbon under grasslands is estimated to take a minimum of 150–500 years. Our study confirms that C4 grass cover has declined over the past 100 years, although isolated C3 trees or shrubs were not uncommon on the historic C4-dominated grasslands. We find evidence in surface soil layers for a modern C3 plant expansion reflected in the substantial shift of SOM δ 13C values from C4 grasses to C3 shrublands.

Phylogenetic relationships among social parasites and their hosts in the ant tribe Tetramoriini (Hymenoptera: Formicidae)

The phylogenetic relationships among Palaearctic species of the ant genus Tetramorium and its social parasites of the genera Strongylognathtus, Anergates and Teletomyrmex, were investigated electrophoretically at 21 presumptive enzyme loci. The data set comprising 33 species was analysed with distance (UPGMA, Neighbor-joining and least squares statistics) and parsimony methods (independent allele, minimum turnover and mutation coding) in order to rule out analysis-dependent effects. Several groupings were consistently resolved by all procedures. Observed branching patterns support the placement of the three parasite genera and their hosts into the Palaearctic species group of Tetramorium (tribe Tetramoriini). The genus Strongylognathus forms a monophyletic group in which the slave-makers of the S. huberi group constitute the sister group of the inquilines S. testaceus and S. karawajewi (S. testaceus group). Most species of the S. huberi group show very low genetic differentiation. However, little consensus has been found with regard to which Tetramorium species are the closest relatives of Strongylognathus.According to the electrophoretic data, social parasitism in Palaearctic tetramoriine ants has evolved independently at least twice. Though inquilinism once arose from slave-making ancestors in Strongylognathus, the extreme inquilines Anergates atratulus and Teleutomyrmex schneideri are clearly set apart from the Strongylognathus clade in phylogenetic analyses. Thus, extreme inquilinism cannot be regarded as the endpoint of a single parasitic lineage in the Tetramoriini. In these highly advanced inquilines, evolutionary rates at allozyme loci appear to be higher than those of their Tetramorium hosts. The results do not unambiguously reveal whether Anergates and Teleutomyrmex arose jointly or independently from Tetramorium ancestors. However, a combined analysis using all available evidence supports the former hypothesis. The finding that the Tetramorium parasites are not the closest relatives of their respective host species is discussed in relation to current theories for the evolution of social parasitism.

Isotope hydrological study of Pulau Langkawi, Malaysia

A survey on the stable isotopes and radioisotopes of Pulau Langkawi have been carried out between 1985 and 1989. Groundwater, river water, spring water and sea water were sampled every year whereas rain water was sampled on a monthly basis. The monthly rainwater showed variation in stable isotopes content. But the groundwater response to this variation is very slow with an average 18 0 value of -6.5%0. From the prepared models and based on the 18 0 value, the global minimum turnover time for Pulau Langkawi is between eight to ten months. The Meteoric Water Line for Langkawi was established as oD = 8.0 18 0 + 13 .7. Based on the stable isotopes and physico-chemical data, the wells are locally recharged by rainwater. Some of the wells are also recharged by nearby rivers. At the present rate of pumping there would be no intrusion of sea water into the studied aquifers. The h igh chloride content in some wells are of local feature, due to evaporation. The chloride content at hot springs may originate from mixing with sea water.

Scanning Force Microscopy Images of Cytochrome c Oxidase Immobilized in an Electrode-Supported Lipid Bilayer Membrane

Scanning force microscopic images of cytochrome c oxidase immobilized within an electrode-supported lipid bilayer membrane are reported. These images represent the first direct evidence that the microscopic architecture of this important model system effectively mimics the microstructure proposed for the inner mitochondrial membrane. The images reveal (1) that the oxidase is present as monomers and small aggregates within the supported membrane and (2) that the oxidase constitutes ∼20% of the lipid bilayer membrane. The latter finding allows an estimation of the lower limit for the minimum turnover rate (∼0.5 electrons/s) required for the transition of the oxidase from its resting to pulsed kinetic state.

THE ROLE OF NITROGEN NUTRITION IN HIGH‐TEMPERATURE TOLERANCE OF THE KELP, LAMINARIA SACCHARINA (CHROMOPHYTA)1

ABSTRACTMechanisms of high‐temperature tolerance in the kelp Laminaria saccharina (L.) Lamour. were examined by comparing a heat‐tolerant ecotype from Long Island Sound (LIS), New York, and a population from the Atlantic (ATL) coast of Maine. Greater heat tolerance was not attributable to greater thermal stability of the photosynthetic apparatus: LIS and ATL plants exhibited similar short‐term effects of high temperature on photosynthetic capacity (Pmax) and quantum yield (estimated as the ratio of variable to maximum chlorophyll fluorescence, Fv/Fm. As LIS plants had consistently higher N and protein content than ATL plants, the interaction between nitrogen nutrition and high‐temperature tolerance was examined. When grown under high N supply and optimal temperature (12° C), LIS plants had a higher density of photosystem II reaction centers (RCII), higher activity of two Calvin cycle enzymes (ribulose bisphosphate carboxylase oxygenase [RUBISCO] and NADP‐dependent glyceraldehyde‐3‐phosphate dehydrogenase [G3PDH]), and higher Pmax and Fv/Fm than ATL plants. Individual ATL plants, furthermore, exhibited close correlations of RCII density and enzyme activity with N and/or protein content. Variation in RCII density and enzyme activity, in turn, largely accounted for plant‐to‐plant differences in Pmax and Fv/Fm. Relationships among these parameters were generally weak or lacking among individual LIS plants grown under optimal conditions, apparently because luxury N consumption resulted in excess reserves of photosynthetic apparatus components. Exposure of N‐replete LIS and ATL plants to a superoptimal temperature (22° C) for 4 days caused an increase in the minimum turnover time of the photosynthetic apparatus (tau) and a decrease in Pmax, but had no consistent effect on Fv/Fm RCII density, PSU size (chlorophyll a/RCII), or enzyme activities. When plants were subjected to concurrent N limitation and heat stress, however, LIS and ATL populations exhibited quite different responses. All photosynthetic parameters of N‐limited ATL plants declined sharply in response to high temperature, resulting in a negative rate of daily net C fixation. In contrast, LIS plants showed a reduction in PSU size, but maintained other parameters, including daily C fixation, at levels similar to those of N‐limited plants at optimal temperature. Overall, the ability of LIS plants to accumulate and maintain high N reserves appears to be critical for heat tolerance and, therefore, for survival during summer periods of simultaneous low N supply and superoptimal temperature. ATL plants, which also experience low summer N supply but not superoptimal temperatures, do not accumulate large reserves of nitrogenous components and are unable to tolerate the combined stress. Because low N supply often co‐occurs with high temperatures in temperate marine systems, large‐scale declines in algal productivity, such as during El Niño events, are probably due to the interactive effect of N limitation and heat stress.

Factors affecting the estimate of primary production from space

Remote sensing of primary production in the euphotic zone has been based mostly on visible‐band water‐leaving radiance measured with the coastal zone color scanner. There are some robust, simple relationships for calculating integral production based on surface measurements, but they also require knowledge of photoadaptive parameters such as maximum photosynthesis which currently cannot be obtained from space. A 17,000‐station data set is used to show that space‐based estimates of maximum photosynthesis could improve predictions of ψ, the water column light utilization index, which is an important term in many primary productivity models. Temperature is also examined as a factor for predicting hydrographic structure and primary production. A simple model is used to relate temperature and maximum photosynthesis; the model incorporates (1) the positive relationship between maximum photosynthesis and temperature and (2) the strongly negative relationship between temperature and nitrate in the ocean (which directly affects maximum growth rates via nitrogen limitation). Since these two factors relate to carbon and nitrogen, “balanced carbon/nitrogen assimilation” was calculated assuming the Redfield ratio. It is expected that the relationship between maximum balanced carbon assimilation versus temperature is concave‐down, with the peak dependent on nitrate uptake kinetics, temperature‐nitrate relationships, and the carbon/chlorophyll ratio. These predictions were compared with sea truth data. The minimum turnover time for nitrate was also calculated using this approach. Lastly, sea surface temperature gradients were used to predict the slope of isotherms (a proxy for the slope of isopycnals in many waters). Sea truth data show that at size scales of several hundred kilometers, surface temperature gradients can provide information on the slope of isotherms in the top 200 m of the water column. This is directly relevant to the supply of nutrients into the surface mixed layer, which is useful for predicting integral biomass and primary production.