Taxonomic Variation Research Articles

High taxonomic variability despite stable functional structure across microbial communities.

Understanding the processes that are driving variation of natural microbial communities across space or time is a major challenge for ecologists. Environmental conditions strongly shape the metabolic function of microbial communities; however, other processes such as biotic interactions, random demographic drift or dispersal limitation may also influence community dynamics. The relative importance of these processes and their effects on community function remain largely unknown. To address this uncertainty, here we examined bacterial and archaeal communities in replicate 'miniature' aquatic ecosystems contained within the foliage of wild bromeliads. We used marker gene sequencing to infer the taxonomic composition within nine metabolic functional groups, and shotgun environmental DNA sequencing to estimate the relative abundances of these groups. We found that all of the bromeliads exhibited remarkably similar functional community structures, but that the taxonomic composition within individual functional groups was highly variable. Furthermore, using statistical analyses, we found that non-neutral processes, including environmental filtering and potentially biotic interactions, at least partly shaped the composition within functional groups and were more important than spatial dispersal limitation and demographic drift. Hence both the functional structure and taxonomic composition within functional groups of natural microbial communities may be shaped by non-neutral and roughly separate processes.

Formation of groupings of mayfly larvae (Ephemeroptera) in the area of small hydrological structures, in the streams of the Kamienica Nawojowska river basin (the Sądeckie Beskids, Poland)

Abstract Anthropogenic modification of abiotic factor in turn influencez biotic communities. The aim of this study was to characterise clusters of mayflies in selected streams of Kamienica Nawojowska river basin in conjunction with small, lateral hydrological structures that have been built in this area. There was an attempt to determine whether and to what extent small lateral hydrological structures affect larvae of mayflies in the examined mountain streams. An analysis of the taxonomic composition of mayfly clusters in the examined stream sections was carried out. For this purpose, the author described the taxonomic wealth, variation in the density of organisms, the domination structure within taxonomic groups and trophic functional groups, taxonomic variation (based on the Shannon-Winner factor), constancy of occurrence (according to the Szujecki formula) as well as faunistic similarity (according to the Jaccard formula). An emphasis was also placed on the species included in the Red List of Vulnerable and Endangered Species in Poland (2002). The obtained results indicate a high taxonomic richness and a large diversity of mayfly fauna on the examined stream sections. There were no significant differences, however, in this aspect between posts situated upstream and downstream from the hydrological structures. The formation of clusters was influenced not so much by small hydrological structures as by other abiotic factors such as the nature of the bottom substrate, the way in which the basin is used, the location of a particular post on a particular watercourse section as well as other anthropogenic activities (e.g. those related to forest management). A comparison of the obtained data with the results of the research conducted before the completion of major regulatory works in Kamienica Nawojowska river basin showed that the mayfly fauna had preserved a large taxonomic richness, although some changes had occurred in the structure of the clusters. However, further research related to this issue is needed, especially in other river basins of the Beskids.

Temperature Sensitivity as a Microbial Trait Using Parameters from Macromolecular Rate Theory.

The activity of soil microbial extracellular enzymes is strongly controlled by temperature, yet the degree to which temperature sensitivity varies by microbe and enzyme type is unclear. Such information would allow soil microbial enzymes to be incorporated in a traits-based framework to improve prediction of ecosystem response to global change. If temperature sensitivity varies for specific soil enzymes, then determining the underlying causes of variation in temperature sensitivity of these enzymes will provide fundamental insights for predicting nutrient dynamics belowground. In this study, we characterized how both microbial taxonomic variation as well as substrate type affects temperature sensitivity. We measured β-glucosidase, leucine aminopeptidase, and phosphatase activities at six temperatures: 4, 11, 25, 35, 45, and 60°C, for seven different soil microbial isolates. To calculate temperature sensitivity, we employed two models, Arrhenius, which predicts an exponential increase in reaction rate with temperature, and Macromolecular Rate Theory (MMRT), which predicts rate to peak and then decline as temperature increases. We found MMRT provided a more accurate fit and allowed for more nuanced interpretation of temperature sensitivity in all of the enzyme × isolate combinations tested. Our results revealed that both the enzyme type and soil isolate type explain variation in parameters associated with temperature sensitivity. Because we found temperature sensitivity to be an inherent and variable property of an enzyme, we argue that it can be incorporated as a microbial functional trait, but only when using the MMRT definition of temperature sensitivity. We show that the Arrhenius metrics of temperature sensitivity are overly sensitive to test conditions, with activation energy changing depending on the temperature range it was calculated within. Thus, we propose the use of the MMRT definition of temperature sensitivity for accurate interpretation of temperature sensitivity of soil microbial enzymes.

Estimation of the occupancy of butterflies in diverse biogeographic regions

Aim We explored the extent to which occupancy of butterflies within three biogeographic regions could be explained by vegetation structure and composition, topography and other environmental attributes; whether results were consistent among regions; and whether assumptions of closure were met with assemblage-level sampling designs. Location Chesapeake Bay Lowlands (Virginia), central Great Basin (Nevada) and western Great Basin (Nevada and California) (all USA). Methods We applied single-season occupancy models that either assumed closure or relaxed the closure assumption to data from 2013 and 2014 for 13–15 species in each region. Results Maximum single-year estimates of detection probabilities ranged from 0.14 to 0.99, and single-year occupancy from 0.28 to 0.98. The assumption of closure was met for a maximum of 54% of the species in a given region and year. Detection probabilities of > 90% of the species in each region increased as the categorical abundance of nectar or mud increased. Measures of the dominance or abundance of deciduous woody species and structural heterogeneity were included in the greatest number of occupancy models for the Chesapeake Bay Lowlands, which may in part reflect the intensity of browsing by white-tailed deer (Odocoileus virginianus). Elevation and precipitation were prominent covariates in occupancy models for Great Basin butterflies. Main conclusions Because occupancy models do not rely on captures or observations of multiple individuals in a population, they potentially can be applied to a relatively high proportion of the species in an assemblage. However, estimation of occupancy is complicated by taxonomic, temporal and spatial variation in phenology. In multiple, widely divergent ecosystems, all or some associations between covariates and detection probability or occupancy for at least one-third of the species could not be estimated, often because a given species rarely was detected at locations with relatively low or high values of a covariate. Despite their advantages, occupancy models may leave unexplained the environmental associations with the distributions of many species.

Polar Lipids Analysis of Cultured Phytoplankton Reveals Significant Inter-taxa Changes, Low Influence of Growth Stage, and Usefulness in Chemotaxonomy.

The high lipid diversity of microalgae has been used to taxonomically differentiate phytoplankton taxa at the class level. However, important lipids such as phospholipids (PL) and betaine lipids (BL) with potential chemotaxonomy application in phytoplankton ecology have been scarcely studied. The chemotaxonomy value of PL and BL depends on their intraspecific extent of variation as microalgae respond to external changing factors. To determine such effects, lipid class changes occurring at different growth stages in 15 microalgae from ten different classes were analyzed. BL occurred in 14 species and were the less affected lipids by growth stage with diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-b-alanine (DGTA) showing the highest stability. PL were more influenced by growth stage with phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidyletanolamine (PE) declining towards older culture stages in some species. Glycolipids were the more common lipids, and no evident age-related variability pattern could be associated to taxonomic diversity. Selecting BL and PL as descriptor variables optimally distinguished microalgae taxonomic variability at all growth stages. Principal coordinate analysis arranged species through a main tendency from diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-b-alanine (DGCC) containing species (mainly dinoflagellates and haptophytes) to DGTA or PC containing species (mainly cryptophytes). Two diatom classes with similar fatty acid profiles could be distinguished from their respective content in DGTA (Bacillariophyceae) or DGCC (Mediophyceae). In green lineage classes (Trebouxiophyceae, Porphyridophyceae, and Chlorodendrophyceae), PC was a better descriptor than BL. BL and PL explained a higher proportion of microalgae taxonomic variation than did fatty acids and played a complementary role as lipid markers.

Spatial and temporal distribution of mercury and methylmercury in bivalves from the French coastline

Marine mercury (Hg) concentrations have been monitored in the French coastline for the last half a century using bivalves. The analyses presented in this study concerned 192 samples of bivalves (mussels: Mytilus edulis and Mytilus galloprovincialis and oysters: Crassostrea gigas and Isognomon alatus) from 77 sampling stations along the French coast and in the French Antilles sea. The goals of this study were to assess MeHg levels in various common bivalves from French coastline, and to identify possible geographic, taxonomic or temporal variations of concentrations. We show that the evolution of methylmercury (MeHg) concentrations covary with total mercury (HgT) concentrations. Moreover, in most of the study sites, HgT concentrations have not decreased since 1987, despite regulations to decrease or ban mercury used for anthropic activities.

Functional microbial distribution in the ocean

Marine Microbiome Bucketsful of genome data for marine microorganisms are available. Although taxonomic patterns in the data are carefully sifted for meaning, Louca et al. show that taxonomy alone does not represent community structure. Meta-analysis of the data gathered during the Tara Oceans project classified over 30,000 bacteria and archaea into functional metabolic groups ranging from photoautotrophy and nitrogen fixation to sulfate respiration. Disentangling functional variation from taxonomic variation indicates that environmental conditions select from a global marine “seedbank” for function, not taxonomy. ![Figure][1] Functional and taxonomic variation can be distinguished in Tara Oceans microbiome data. PHOTO: CHRISTIAN SARDET Science , this issue p. [1272][2] [1]: pending:yes [2]: /lookup/doi/10.1126/science.aaf4507

Decoupling function and taxonomy in the global ocean microbiome

Microbial metabolism powers biogeochemical cycling in Earth's ecosystems. The taxonomic composition of microbial communities varies substantially between environments, but the ecological causes of this variation remain largely unknown. We analyzed taxonomic and functional community profiles to determine the factors that shape marine bacterial and archaeal communities across the global ocean. By classifying >30,000 marine microorganisms into metabolic functional groups, we were able to disentangle functional from taxonomic community variation. We find that environmental conditions strongly influence the distribution of functional groups in marine microbial communities by shaping metabolic niches, but only weakly influence taxonomic composition within individual functional groups. Hence, functional structure and composition within functional groups constitute complementary and roughly independent "axes of variation" shaped by markedly different processes.

Larval fish abundance in relation to environmental variables in two Texas Gulf Coast rivers

ABSTRACTPhenology of fish spawning in lotic ecosystems depends on interactions between species life history strategies and patterns of environmental variation related to hydrology and seasonality. To further study these relationships, we examined patterns of larval fish abundance in relation to discharge and other environmental variables in the Brazos and Trinity rivers, Texas. From March 2013 to March 2014, environmental data and larval fishes were collected twice each month using drift nets. Multivariate analyses indicated that, at both study sites, water temperature was the primary mechanism driving temporal and taxonomic variation in larval fish assemblage structure at the family level. However, in the Trinity River, assemblage structure was significantly associated with discharge, albeit to a lesser degree than with water temperature. Cyprinid protolarvae dominated catches in both rivers and did not seem to be constrained by any aspect of the flow regime, as evidenced by their high abundance throughout the reproductive season (April–September). Analysis of larval fish abundance at the family level compromised our ability to infer spawning dynamics of species classified as fluvial specialists. Further research enabling identification of larvae to species-level is needed to elucidate how flow regime components influence reproduction and recruitment of fluvial specialists.

Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT.

Lysorophians are a group of early tetrapods with extremely elongate trunks, reduced limbs, and highly reduced skulls. Since the first discovery of this group, general similarities in outward appearance between lysorophians and some modern lissamphibian orders (specifically Urodela and Gymnophiona) have been recognized, and sometimes been the basis for hypotheses of lissamphibian origins. We studied the morphology of the skull, with particular emphasis on the neurocranium, of a partial growth series of the lysorophian Brachydectes newberryi using x-ray micro-computed tomography (μCT). Our study reveals similarities between the braincase of Brachydectes and brachystelechid recumbirostrans, corroborating prior work suggesting a close relationship between these taxa. We also describe the morphology of the epipterygoid, stapes, and quadrate in this taxon for the first time. Contra the proposals of some workers, we find no evidence of expected lissamphibian synapomorphies in the skull morphology in Brachydectes newberryi, and instead recognize a number of derived amniote characteristics within the braincase and suspensorium. Morphology previously considered indicative of taxonomic diversity within Lysorophia may reflect ontogenetic rather than taxonomic variation. The highly divergent morphology of lysorophians represents a refinement of morphological and functional trends within recumbirostrans, and is analogous to morphology observed in many modern fossorial reptiles.

Effects of water level fluctuation on phytoplankton succession in Poyang Lake, China – A five year study

Poyang Lake is the largest freshwater lake in the Yangtze floodplain in China, with dramatic seasonal water level changes each year. The quarterly monitoring data from 2009 to 2013 was used to study the impact of the water level fluctuation on the phytoplankton biomass and taxonomic composition variation in different hydrological phases in Poyang Lake. Bacillariophyta species are generally dominant in Poyang Lake, constituting more than 50% of the total phytoplankton biomass, except from July 2009 and January 2012. The results that phytoplankton biomass increased gradually from 2009 to 2013, especially after 2012, indicated there is some time lag in the response of phytoplankton biomass to nutrient loading in Poyang Lake. Our results support the hypothesis that water level fluctuation exert great influence on phytoplankton succession and hydrology fluctuations have an indirect impact on a decrease of Cyanophyta biomass with regard to dilution of nutrients (P, N) in Poyang Lake. This study indicates that we should keep the water level changes more or less as they are because ecologically relevant in Poyang Lake.

Changes in patterns of biodiversity of marine mollusks along the Brazilian coast during the late Holocene inferred from shell-mound (sambaquis) data

An archaeological dimension expands the concept of biodiversity by generating long-term perspectives, combining multiple approaches and methodologies to enhance understanding of environmental changes. Aiming to investigate the patterns of biodiversity of marine mollusks over time, a comparison was made between three sets of archaeological sites (shellmounds) located in three geographic areas of the south-southeastern Brazilian coast. Sites dated between 1000–2000 and 4000–5000 yr BP were analyzed. A total of 37 bivalves and 26 gastropods were recorded. To describe the malacological community two indices of taxonomic diversity were used: average taxonomic distinctness and variation in taxonomic distinctness. The results showed a tendency of reduction in biodiversity patterns in the last 5000 years measured as average taxonomic distinctness. The observed reduction in biodiversity does not seem to be directly related to climate change over the period and there is a lack of data which could demonstrate any association between reduction in biodiversity and cultural causes such as preferences, technical level or food taboos of the prehistoric human populations. On the other hand, changes in sea level during this period are well documented and have been responsible for dramatic changes along the coast of this region. Therefore, it is likely that it could have affected local biodiversity and caused the observed pattern.

Seasonal variations in macrobenthic taxonomic diversity and the application of taxonomic distinctness indices in Bohai Bay, northern China

Taxonomic diversity indices have a number of desirable properties as indicators in the assessment of environmental quality, and have become an important measure in biodiversity studies. Macrobenthic taxonomic variations were studied in Bohai Bay, northern China, an area under threat from rapid human development. Four seasonal cruise datasets were collected between 2006 and 2007. Environmental conditions exhibited large fluctuations due to human development; nitrogen and phosphorus were the main environmental stressors. A total of 97 macrofauna taxa were identified belonging to 88 genera, 72 families, 36 orders, 14 classes, and nine phyla. Analysis of similarity indicated that there were significant assemblage differences across sampling stations as well as seasons. Four taxonomic indices, taxonomic diversity (Δ), taxonomic distinctness (Δ*), average taxonomic distinctness (Δ+), and variation in taxonomic distinctness (Λ+) were calculated using abundance data. Among the stations and seasons, there were greater variations in both Δ and Λ+ than in Δ* and Δ+. The funnel plot of Δ+ could identify disturbed stations to some extent, but was not always a strong indicator of disturbance. The Δ+ performance was better in autumn than in spring, but could not identify a disturbed station in autumn due to a low number of species. The efficiency of taxonomic distinctness may depend on taxa or the pollution indicators. Taxonomic distinctness indices can be effective at assessing environmental degradation when correctly applied; however, they are unsuitable for directly assessing environmental quality in a new area prior to efficiency testing.

Hierarchical analysis of taxonomic variation in intraspecific competition across fish species.

The nature and intensity of intraspecific competition can vary greatly among taxa, yet similarities in these interactions can lead to similar population dynamics among related organisms. Variation along the spectrum of intraspecific competition, with contest and scramble competition as endpoints, leads to vastly different responses to population density. Here we investigated the diversity of intraspecific competition among fish species, predicting that functional forms of density-dependent reproduction would be conserved in related taxa. Using a hierarchical model that links stock-recruitment parameters among populations, species, and orders, we found that the strength of overcompensation, and therefore the type of intraspecific competition, is tightly clustered within taxonomic groupings, as species within an order share similar degrees of compensation. Specifically, species within the orders Salmoniformes and Pleuronectiformes exhibited density dependence indicative of scramble competition (overcompensation) while the orders Clupeiformes, Gadiformes, Perciformes, and Scorpaeniformes exhibited dynamics consistent with contest competition (compensation). Maximum potential recruitment also varied among orders, but with less clustering across species. We also tested whether stock-recruitment parameters correlated with maximum body length among species, but found no strong relationship. Our results suggest that much of the variation in the form of density-dependent reproduction among fish species may be predicted taxonomically due to evolved life history traits and reproductive behaviors.

Functional Diversity as a New Framework for Understanding the Ecology of an Emerging Generalist Pathogen

Emerging infectious disease outbreaks are increasingly suspected to be a consequence of human pressures exerted on natural ecosystems. Previously, host taxonomic communities have been used as indicators of infectious disease emergence, and the loss of their diversity has been implicated as a driver of increased presence. The mechanistic details in how such pathogen-host systems function, however, may not always be explained by taxonomic variation or loss. Here we used machine learning and methods based on Gower's dissimilarity to quantify metrics of invertebrate functional diversity, in addition to functional groups and their taxonomic diversity at sites endemic and non-endemic for the model generalist pathogen Mycobacterium ulcerans, the causative agent of Buruli ulcer. Changes in these metrics allowed the rapid categorisation of the ecological niche of the mycobacterium's hosts and the ability to relate specific host traits to its presence in aquatic ecosystems. We found that taxonomic diversity of hosts and overall functional diversity loss and evenness had no bearing on the mycobacterium's presence, or whether the site was in an endemic area. These findings, however, provide strong evidence that generalist environmentally persistent bacteria such as M. ulcerans can be associated with specific functional traits rather than taxonomic groups of organisms, increasing our understanding of emerging disease ecology and origin.

Phenological sensitivity to climate across taxa and trophic levels.

Differences in phenological responses to climate change among species can desynchronise ecological interactions and thereby threaten ecosystem function. To assess these threats, we must quantify the relative impact of climate change on species at different trophic levels. Here, we apply a Climate Sensitivity Profile approach to 10,003 terrestrial and aquatic phenological data sets, spatially matched to temperature and precipitation data, to quantify variation in climate sensitivity. The direction, magnitude and timing of climate sensitivity varied markedly among organisms within taxonomic and trophic groups. Despite this variability, we detected systematic variation in the direction and magnitude of phenological climate sensitivity. Secondary consumers showed consistently lower climate sensitivity than other groups. We used mid-century climate change projections to estimate that the timing of phenological events could change more for primary consumers than for species in other trophic levels (6.2 versus 2.5-2.9 days earlier on average), with substantial taxonomic variation (1.1-14.8 days earlier on average).

Six years of observation of airborne and deposited pollen in central European Russia: first results

The aim of the study was to compare the pollen spectra recorded in rural and urban environments in order to examine whether pollen data obtained in the urban environment could also represent the situation in surrounding rural areas and how urban planting affects the regional pollen spectrum. Daily airborne pollen observations were performed with a volumetric Hirst type trap in Moscow (Russia). Modified Tauber traps were located in the Moscow region. The Tauber traps were installed and treated according to Pollen Monitoring Programme (PMP) guidelines. Spearman correlation coefficients were determined between the percentage of total pollen recorded in the Tauber and Hirst type samplers. The data showed that the Tauber spectra are characterised by higher taxonomic variability, mainly due to the greater occurrence of local herbaceous plants. Pollen types registered by Hirst type samplers were predominantly represented by anemophilous arboreal species, used in urban planting. A significant correlation for annual sums was only observed for Betula pollen, the most abundant component in both sampler types. Data obtained in big cities for dominant taxa can be extrapolated to the surrounding rural territories. The simultaneous use of volumetric and gravimetric samplers can be very useful for palaeo-ecological studies to evaluate the presence of local and transported pollen.

Scaling leaf respiration with nitrogen and phosphorus in tropical forests across two continents.

Summary Leaf dark respiration (R dark) represents an important component controlling the carbon balance in tropical forests. Here, we test how nitrogen (N) and phosphorus (P) affect R dark and its relationship with photosynthesis using three widely separated tropical forests which differ in soil fertility. R dark was measured on 431 rainforest canopy trees, from 182 species, in French Guiana, Peru and Australia. The variation in R dark was examined in relation to leaf N and P content, leaf structure and maximum photosynthetic rates at ambient and saturating atmospheric CO 2 concentration.We found that the site with the lowest fertility (French Guiana) exhibited greater rates of R dark per unit leaf N, P and photosynthesis. The data from Australia, for which there were no phylogenetic overlaps with the samples from the South American sites, yielded the most distinct relationships of R dark with the measured leaf traits.Our data indicate that no single universal scaling relationship accounts for variation in R dark across this large biogeographical space. Variability between sites in the absolute rates of R dark and the R dark : photosynthesis ratio were driven by variations in N‐ and P‐use efficiency, which were related to both taxonomic and environmental variability.

Melting pot of biodiversity: first insights into the evolutionary patterns of the Colchic bramble flora (RubussubgenusRubus, Rosaceae)

The Caucasus is a biodiversity hotspot of global significance, containing a number of highly diverse and species-rich plant taxa. The region is also thought to be an important evolutionary hotspot for Rubus subgenus Rubus (brambles). However, Caucasian brambles have only been poorly studied to date and our knowledge of their evolutionary mechanisms, systematics and taxonomic variability remains rudimentary. Therefore, the objectives of this study were to shed light on the evolution, diversity and reproduction modes of Rubus in one of the two Caucasian glacial refugia, Colchis. Flow cytometry measurements were used to estimate DNA ploidy, a flow cytometric seed screen was conducted to determine reproduction mode and Sanger sequencing of two non-coding plastid regions was used to reveal phylogenetic patterns. The most common ploidy level was tetraploid, followed by diploid and (rarely) triploid. Intra-individual variation in reproduction mode was low, as the morphoseries Glandulosi and Radula exhibited strict sexuality and other taxa were mostly apomictic. A few exceptions were observed that deserve further attention, e.g. sexuality induced hypothetically by haploid pollen or by environmental conditions, a high proportion of triploid embryos or polyspermy. Plastid haplotype variability revealed specific, ancient evolutionary patterns with limited involvement of extant diploid taxa and recent isolation from European brambles. We provide the first insight into the variability and evolution of Colchic brambles, which serves as a starting point for further systematic and evolutionary studies.

Taxonomic and Environmental Variability in the Elemental Composition and Stoichiometry of Individual Dinoflagellate and Diatom Cells from the NW Mediterranean Sea.

Here we present, for the first time, the elemental concentration, including C, N and O, of single phytoplankton cells collected from the sea. Plankton elemental concentration and stoichiometry are key variables in phytoplankton ecophysiology and ocean biogeochemistry, and are used to link cells and ecosystems. However, most field studies rely on bulk techniques that overestimate carbon and nitrogen because the samples include organic matter other than plankton organisms. Here we used X-ray microanalysis (XRMA), a technique that, unlike bulk analyses, gives simultaneous quotas of C, N, O, Mg, Si, P, and S, in single-cell organisms that can be collected directly from the sea. We analysed the elemental composition of dinoflagellates and diatoms (largely Chaetoceros spp.) collected from different sites of the Catalan coast (NW Mediterranean Sea). As expected, a lower C content is found in our cells compared to historical values of cultured cells. Our results indicate that, except for Si and O in diatoms, the mass of all elements is not a constant fraction of cell volume but rather decreases with increasing cell volume. Also, diatoms are significantly less dense in all the measured elements, except Si, compared to dinoflagellates. The N:P ratio of both groups is higher than the Redfield ratio, as it is the N:P nutrient ratio in deep NW Mediterranean Sea waters (N:P = 20–23). The results suggest that the P requirement is highest for bacterioplankton, followed by dinoflagellates, and lowest for diatoms, giving them a clear ecological advantage in P-limited environments like the Mediterranean Sea. Finally, the P concentration of cells of the same genera but growing under different nutrient conditions was the same, suggesting that the P quota of these cells is at a critical level. Our results indicate that XRMA is an accurate technique to determine single cell elemental quotas and derived conversion factors used to understand and model ocean biogeochemical cycles.