Changes In Nutrient Supply Research Articles

Increase in Paleoproductivity Driven by Strengthening of Indian Summer Monsoon During Past ~14kyrs: Evidenced by Biogenic Silica Accumulation Rates at Southeastern Arabian Sea

We analysed the BSi (Biogenic Silica) contents of the marine core SK-313/1 from the southeastern Arabian Sea which is dated up to ~14.5 kyr BP. Results show that the maximum and minimum BSi contents are 2.5 and 0.5%, respectively. This is because of the low supply of silica skeleton and the high dissolution and dilution of terrigenous materials. The BSi mass accumulation rates indicate a trend of reduced paleoproductivity during the late Glacial period and increase during the Holocene, with global climatic shifts. Insolation changes at low latitudes, which regulate temperatures, may affect nutrient availability and, consequently productivity variations on a glacial–interglacial timescale. Notably, millennial events like the Younger Dryas (YD) periods, exhibited lower paleoproductivity, in contrast to the Bølling/Allerød (B-A) period and the middle Holocene, which displayed elevated levels of paleoproductivity. These millennial-scale fluctuations in siliceous productivity may be due to the changes in nutrient supply caused by the Indian summer monsoon (ISM). The period of increased paleoproductivity could be influenced by intensified chemical weathering and a boosted nutrient supply, which are consequences of the strengthened ISM during periods of relatively higher temperature.

Phytoplankton stoichiometry along the salinity gradient under limited nutrient and light supply.

Ongoing climate warming alters precipitation and water column stability, leading to salinity and nutrient supply changes in the euphotic zone of many coastal ecosystems and semi-enclosed seas. Changing salinity and nutrient conditions affect phytoplankton physiology by altering elemental ratios of carbon (C), nitrogen (N) and phosphorus (P). This study aimed to understand how salinity stress and resource acquisition affect phytoplankton stoichiometry. We incubated a phytoplankton polyculture composed of 10 species under different light, inorganic nutrient ratio and salinity levels. At the end of the incubation period, we measured particulate elemental composition (C, N and P), chlorophyll a and species abundances. The phytoplankton polyculture, dominated by Phaeodactylum tricornutum, accumulated more particulate organic carbon (POC) with increasing salinity. The low POC and low particulate C:N and C:P ratios toward 0psu suggest that the hypoosmotic conditions highly affected primary production. The relative abundance of different species varied with salinity, and some species grew faster under low nutrient supply. Still, the dominant diatom regulated the overall POC of the polyculture, following the classic concept of the foundation species.

Density and Composition of Cohabiting Bacteria in Chlorella vulgaris CCAP 211/21A Is Influenced by Changes in Nutrient Supply

Microalgae have considerable potential as a renewable feedstock for biochemical and bioethanol production that can be employed in processes associated with carbon capture. Large-scale microalgae cultivations are often non-axenic and are often cohabited by bacteria. A better understanding of the influence of cohabiting bacteria on microalgae productivity is required to develop sustainable synthetic co-culture processes at scale. Nutrient limitation is a frequently employed strategy in algal cultivations to accumulate energy reserves, such as lipids and carbohydrates. Here, a non-axenic culture of an estuarine green microalga, Chlorella vulgaris CCAP 211/21A, was studied under nutrient replete and deplete conditions to assess how changes in nutrient supply influenced the cohabiting bacterial population and its association with intracellular carbohydrate accumulations in the alga. Nutrient limitation resulted in a maximum carbohydrate yield of 47%, which was 74% higher than that in nutrient replete conditions. However, the latter condition elicited a 2-fold higher carbohydrate productivity. Three cohabiting bacterial isolates were cultivable from the three culture conditions tested. These isolates were identified using the 16S rRNA gene sequence to belong to Halomonas sp. and Muricauda sp. The composition of the bacterial population varied significantly between the growth conditions and time points. In all cases and at all time points, the dominant species was Halomonas isolates. Nutrient depletion resulted in an apparent loss of Muricauda sp. This finding demonstrates that nutrient supply can be used to control cohabiting bacterial populations in algal cultures, which will enable the development of synthetic co-culture strategies for improving algae productivity.

Feed restriction of lactating cows triggers acute downregulation of mammary mammalian target of rapamycin signaling and chronic reduction of mammary epithelial mass

While there is generally no consensus about how nutrients determine milk synthesis in the mammary gland, it is likely that the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) plays a role as a key integrator of nutritional and mitogenic signals that can influence a multitude of catabolic and anabolic pathways. The objectives of this study were to evaluate acute changes (<24 h) in translational signaling, in addition to chronic changes (14 d) in mammary gland structure and composition, in response to a severe feed restriction. Fourteen lactating Holstein dairy cows were assigned to either ad libitum feeding (n = 7) or a restricted feeding program (n = 7). Feed-restricted cows had feed removed after the evening milking on d 0. Mammary biopsies and blood samples were collected 16 h after feed removal, after which cows in the restricted group were fed 60% of their previously observed ad libitum intake for the remainder of the study. On d 14, animals were slaughtered and their mammary glands dissected. In response to feed removal, an acute increase in plasma nonesterified fatty acid concentration was observed, concurrent to a decrease in milk yield. In mammary tissue, we observed downregulation of the mTORC1-S6K1 signaling cascade, in addition to reductions in mRNA expression of markers of protein synthesis, endoplasmic reticulum biogenesis, and cell turnover (i.e., transcripts associated with apoptosis or cell proliferation). During the 14 d of restricted feeding, animals underwent homeorhetic adaptation to 40% lower nutrient intake, achieving a new setpoint of 14% reduced milk yield with 18% and 29% smaller mammary secretory tissue DM and CP masses, respectively. On d 14, no treatment differences were observed in markers of protein synthesis or mammary cell turnover evaluated using gene transcripts and immunohistochemical staining. These findings implicate mTORC1-S6K1 in the early phase of the adaptation of the mammary gland's capacity for milk synthesis in response to changes in nutrient supply. Additionally, changes in rates of mammary cell turnover may be transient in nature, returning to basal levels following brief alterations that have sustained effects.

Exploring the relationship between sea ice and phytoplankton growth in the Weddell Gyre using satellite and Argo float data

Abstract. Some of the highest rates of primary production across the Southern Ocean occur in the seasonal ice zone (SIZ), making this a prominent area of importance for both local ecosystems and the global carbon cycle. There, the annual advance and retreat of ice impacts light and nutrient availability, as well as the circulation and stratification, thereby imposing a dominant control on phytoplankton growth. In this study, the drivers of variability in phytoplankton growth between 2002–2020 in the Weddell Gyre SIZ were assessed using satellite net primary production (NPP) products alongside chlorophyll-a and particulate organic carbon (POC) data from autonomous biogeochemical floats. Although the highest daily rates of NPP are consistently observed in the continental shelf region (water depths shallower than 2000 m), the open-ocean region's larger size and longer ice-free season mean that it dominates biological carbon uptake within the Weddell Gyre, accounting for 93 %–96 % of the basin's total annual NPP. Variability in the summer maximum ice-free area is the strongest predictor of inter-annual variability in total NPP across the Weddell Gyre, with greater ice-free area resulting in greater annual NPP, explaining nearly half of the variance (R2=42 %). In the shelf region, the return of sea ice cover controls the end of the productive season. In the open ocean, however, both satellite NPP and float data show that a decline in NPP occurs before the end of the ice-free season (∼ 80 to 130 d after sea ice retreat). Evidence of concurrent increases in float-observed chlorophyll-a and POC suggest that later in the summer season additional factors such as micro-nutrient availability or top-down controls (e.g. grazing) could be limiting NPP. These results indicate that in a warmer and more ice-free Weddell Gyre, notwithstanding compensating changes in nutrient supply, NPP is likely to be enhanced only up to a certain limit of ice-free days.

Analysis of global nutrient gaps and their potential to be closed through redistribution and increased supply.

Global food systems are crucial for sustaining life on Earth. Although estimates suggest that the current production system can provide enough food and nutrients for everyone, equitable distribution remains challenging. Understanding global nutrient distribution is vital for addressing disparities and creating effective solutions for the present and future. This study analyzes global nutrient supply changes to address inadequacies in certain populations using the existing DELTA Model®, which uses aggregates of global food production to estimate nutrient adequacy. By examining the 2020 global food commodity and nutrient distribution, we project future food production in 2050 needs to ensure global adequate nutrition. Our findings reveal that while some nutrients appear to be adequately supplied on a global scale, many countries face national insufficiencies (% supply below the population reference intake) in essential vitamins and minerals, such as vitamins A, B12, B2, potassium, and iron. Closing these gaps will require significant increases in nutrient supply. For example, despite global protein supply surpassing basic needs for the 2050 population, significant shortages persist in many countries due to distribution variations. A 1% increase in global protein supply, specifically targeting countries with insufficiencies, could address the observed 2020 gaps. However, without consumption pattern changes, a 26% increase in global protein production is required by 2050 due to population growth. In this study, a methodology was developed, applying multi-decade linear convergence to sufficiency values at the country level. This approach facilitates a more realistic assessment of future needs within global food system models, such as the DELTA Model®, transitioning from idealized production scenarios to realistic projections. In summary, our study emphasizes understanding global nutrient distribution and adjusting minimum global nutrient supply targets to tackle country-level inequality. Incorporating these insights into global food balance models can improve projections and guide policy decisions for sustainable, healthy diets worldwide.

Reduction in size of the calcifying phytoplankton Calcidiscus leptoporus to environmental changes between the Holocene and modern Subantarctic Southern Ocean

The Subantarctic Zone of the Southern Ocean plays a disproportionally large role on the Earth system. Model projections predict rapid environmental change in the coming decades, including ocean acidification, warming, and changes in nutrient supply which pose a serious risk for marine ecosystems. Yet despite the importance of the Subantarctic Zone, annual and inter-annual time series are extremely rare, leading to important uncertainties about the current state of its ecosystems and hindering predictions of future response to climate change. Moreover, as the longest observational time series available are only a few decades long, it remains unknown whether marine pelagic ecosystems have already responded to ongoing environmental change during the industrial era. Here, we take advantage of multiple sampling efforts – monitoring of surface layer water properties together with sediment trap, seafloor sediment and sediment core sampling – to reconstruct the modern and pre-industrial state of the keystone calcifying phytoplanktonCalcidiscus leptoporus, central to the global marine carbonate cycle. Morphometric measurements reveal that modernC. leptoporuscoccoliths are 15% lighter and 25% smaller than those preserved in the underlying Holocene-aged sediments. The cumulative effect of multiple environmental factors appears responsible for the coccolith size variations since the Last Deglaciation, with warming and ocean acidification most likely playing a predominant role during the industrial era. Notably, extrapolation of our results suggests a future reduction in cell and coccolith size which will have a negative impact on the efficiency of the biological pump in the Southern Ocean through a reduction of carbonate ballasting. Lastly, our results tentatively suggest thatC. leptoporuscoccolith size could be used as a palaeo-proxy for growth rate. Future culture experiments will be needed to test this hypothesis.

ENSO vs glacial-interglacial-induced changes in the Kuroshio-Oyashio transition zone during the Pleistocene

The subarctic front (SAF) in the pelagic North Pacific is the northernmost front of the Kuroshio-Oyashio transition zone separating the subpolar and subtropical gyres and is marked by a strong sea surface temperature gradient. A complex interplay of e.g. variations of currents, the wind system and other forcing mechanisms causes shifts of the SAF’s position on timescales from orbital to interannual. In this study, we present proxy data from the Emperor Seamount chain, which reveal a link between long-term ENSO (El Niño/Southern Oscillation) dynamics in the tropics and shifts of the SAF. Based on sediment core SO264-45-2 from Jimmu Seamount (46°33.792’N, 169°36.072’E) located close to the modern position of the SAF, we reconstruct changes in (sub)surface temperature ((sub)SSTMg/Ca) and δ18Osw-ivc (approximating salinities) via combined Mg/Ca and δ18O analyses of the shallow-dwelling foraminifera Globigerina bulloides and the near-thermocline-dwelling Neogloboquadrina pachyderma, biological productivity (XRF-based Ba/Ti ratios), and terrigenous input via dust (XRF-based Fe). From ~600 to ~280 ka BP we observe significantly higher SSTMg/Ca than after an abrupt change at 280 ka BP. We assume that during this time warmer water from the Kuroshio-Oyashio transition zone reached the core site, reflecting a shift of the SAF from a position at or even north of our study site prior to 280 ka BP to a position south of our study site after 280 ka BP. We propose that such a northward displacement of the SAF between 600-280 ka BP was induced by sustained La Niña-like conditions, which led to increased transport of tropical ocean heat into the Kuroshio-Oyashio transition zone via the Kuroshio Current. After ~280 ka BP, the change to more El Niño-like conditions led to less heat transfer via the Kuroshio Current with the SAF remaining south of the core location. In contrast, our productivity record shows a clear glacial-interglacial pattern that is common in the North Pacific. We assume that this pattern is connected to changes in nutrient supply or utilization, which are not primarily driven by changes of the Kuroshio and Oyashio Currents or the SAF.

The development of human gut microbiota fermentation capacity during the first year of life.

Fermentation capacity of microbial ecosystems intrinsically depends on substrate supply and the ability of a microbial community to deliver monomers for fermentation. In established microbial ecosystems, the microbial community is adapted to efficiently degrade and ferment available biopolymers which is often concurrently reflected in the richness of the microbial community and its functional potential. During the first year of life, the human gut microbial environment is a rather dynamic system that is characterized by a change in physiological conditions (e.g. from aerobic to anaerobic conditions, physical growth of the gastrointestinal tract, development of the intestinal immune system) but also by a change in nutrient supply from a compositionally limited liquid to a diverse solid diet, which demands major compositional and functional changes of the intestinal microbiota. How these transitions link to intestinal microbial fermentation capacity has gained comparatively little interest so far. This mini-review aims to collect evidence that already after birth, there is seeding of a hidden population of various fermentation organisms which remain present at low abundance until the cessation of breastfeeding removes nutritional restrictions of a liquid milk-based diet. The introduction of solid food containing plant and animal material is accompanied by an altering microbiota. The concurrent increases in the abundance of degraders and fermenters lead to higher intestinal fermentation capacity indicated by increased faecal levels of the final fermentation metabolites propionate and butyrate. Recent reports indicate that the development of fermentation capacity is an important step during gut microbiota development, as chronic disorders such as allergy and atopic dermatitis have been linked to lower degradation and fermentation capacity indicated by reduced levels of final fermentation metabolites at 1 year of age.

Integrating the impact of global change on the niche and physiology of marine nitrogen-fixing cyanobacteria.

Marine nitrogen fixation is a major source of new nitrogen to the ocean, which interacts with climate driven changes to physical nutrient supply to regulate the response of ocean primary production in the oligotrophic tropical ocean. Warming and changes in nutrient supply may alter the ecological niche of nitrogen-fixing organisms, or 'diazotrophs', however, impacts of warming on diazotroph physiology may also be important. Lab-based studies reveal that warming increases the nitrogen fixation-specific elemental use efficiency (EUE) of two prevalent marine diazotrophs, Crocosphaera and Trichodesmium, thus reducing their requirements for the limiting nutrients iron and phosphorus. Here, we coupled a new diazotroph model based upon observed diazotroph energetics of growth and resource limitation to a state-of-the-art global model of phytoplankton physiology and ocean biogeochemistry. Our model is able to address the integrated response of nitrogen fixation by Trichodesmium and Crocosphaera to warming under the IPCC high emission RCP8.5 scenario for the first time. Our results project a global decline in nitrogen fixation over the coming century. However, the regional response of nitrogen fixation to climate change is modulated by the diazotroph-specific thermal performance curves and EUE, particularly in the Pacific Ocean, which shapes global trends. Spatially, the response of both diazotrophs is similar with expansion towards higher latitudes and reduced rates of nitrogen fixation in the lower latitudes. Overall, 95%-97% of the nitrogen fixation climate signal can be attributed to the combined effect of temperature on the niche and physiology of marine diazotrophs, with decreases being associated with a reduced niche and increases resulting due to a combination of expanding niche and temperature driven changes to EUE. Climate change impacts on both the niche and physiology of marine diazotrophs interact to shape patterns of marine nitrogen fixation, which will have important implications for ocean productivity in the future.

Nutrigenomics in livestock: potential role in physiological regulation and practical applications

The relationship among nutrition, health, and productivity of livestock is a continuously changing interaction between environment and physiology. As such, understanding how the physiological system is able to adapt to the type and amount of nutrients consumed is central to our ability to care for and manage livestock. Recognition that cells possess proteins with the ability to ‘sense’ and trigger a cascade of biological events in response to nutrient availability is at the core of nutritional genomics (or nutrigenomics) as a field of science. Nutrigenomics is generally defined as the study of the genome-wide influence of nutrition. Certain transcriptional regulators can interact with nutrients and cause large-scale alterations in gene expression, metabolic and signaling pathways, and ultimately tissue function. The advent of high-throughput technologies to study an animal’s microbiome, genome, transcriptome, proteome, and metabolome (i.e. ‘omics’ tools) has been instrumental in moving the field of nutrigenomics forward. Available data from studies with livestock species using targeted or untargeted molecular methods underscore the existence of networks of multiple transcriptional regulators at play in controlling nutrigenomics responses. Fatty acids, amino acids, trace nutrients, and level of feed and energy intake have the strongest reported nutrigenomics potential. An important goal for applying nutrigenomics at the animal level is to uncover key molecular players involved in the physiological adaptations to changes in nutrient supply and environmental conditions.

Evaluating the relevance of species sorting and physiological plasticity of phytoplankton communities grown in a multifactor environment

Abstract The two important mechanisms influencing the response of phytoplankton communities to alterations of abiotic factors in their environment are difficult to distinguish: species sorting resulting from a change in interspecific competitive pressure, and phenotypic plasticity (here explicitly physiological plasticity i.e. species‐specific physiological adjustment). A shift in species composition as well as physiological adjustments in species can lead to changes in fatty acid composition that determine the food quality for zooplankton consumers. We used phytoplankton communities consisting of five species and exposed them to two different light intensities, two light conditions (constant and variable), and two levels of phosphorus supply. Changes in fatty acid and species composition were analyzed. We compared community pairs differing in one factor by calculating the Bray‐Curtis similarity index for the composition of both variables. Comparing the Bray‐Curtis similarity index of the species composition with the index of the fatty acid composition was used to estimate the effects of species sorting and physiological plasticity. Changes in nutrient supply influenced fatty acid responses based on species sorting and physiological plasticity the most. On one hand, the relevance of physiological plasticity was highest at cultivation in different nutrient supplies but the same light environment. Conversely with low nutrients species sorting appeared to dominate the response to changes in light, while at high nutrients physiological plasticity appeared to influence the response. Overall, under low phosphorus supply the communities showed a lower total fatty acid content per carbon and had increased proportions of saturated and monounsaturated fatty acids. Instead, communities in low light produced more of eicosapentaenoic acid. Our results suggest that the relevance of species sorting and physiological plasticity in shaping the community response highly depends on the environmental factors that influence the system. Nutrient supply had the largest effect, while light had more limited conditional effects. However, all of these factors are important in shaping the food quality of the phytoplankton community for higher trophic levels.

Restored riverine wetlands in a headwater stream can simultaneously behave as sinks of N2O and hotspots of CH4 production

Wetlands can improve water quality, but they are also recognized as important sources of greenhouse gases (GHG) such as nitrous oxide (N2O) and methane (CH4). Emissions of these gases from wetland ecosystems, especially those in headwaters, are poorly understood. Here, we determined monthly concentrations of dissolved N2O and CH4 in a headwater stream of the Taihu Lake basin of China that contains both wetland and non-wetland reaches. Daily GHG dynamics in the wetland reach were also investigated. Riverine N2O and CH4 concentrations generally varied within 10–30 nmol L−1 and 0.1–1.5 μmol L−1, respectively. CH4 saturation levels in the wetland reach were about seven times higher than those in the non-wetland reach, but there was no difference in N2O saturation. In the wetland reach, saturation levels of CH4 peaked in July, coincident with a dip in N2O saturation to levels below its saturated solubility. This underscores that hotspots of CH4 production and sinks for N2O can occur occasionally in wetlands in mid-summer, when vegetative growth and microbial activities are high. Diurnal measurements indicated that CH4 saturation in water flows passing through the wetlands from midnight through the early morning can surge to levels 10 times higher than those detected at other times of the day. Simultaneously, saturation levels of N2O decreased by 75%, indicating a net consumption of N2O. Changes in nutrient supply determined by upstream inflows, as well as dissolved oxygen, pH, and other environmental factors mediated by the wetlands, correlate with the differentiated behavior of N2O and CH4 production in wetlands. Additional work will be necessary to confirm the roles of these factors in regulating GHG emissions in riverine wetlands.

Stand age affects fungal community composition in a Central European temperate forest

Fungi are key mediators of ecosystem processes in temperate forests. Hence, understanding of fungal community development is central to better understand the mechanisms driving shifts in ecosystem processes during forest succession. We studied fungal communities in soil, rhizosphere and roots in a Central European forest chronosequence (1–137 years) dominated by Fagus sylvatica and Picea abies. We assessed whether and how fungal community composition and productivity change along the forest age gradient. Stand age did not have any significant effect on fungal ergosterol content but community composition shifted with the stand age. In particular, the composition of the community of root-associated ectomycorrhizal fungi responded to stand age. Relative abundances of different fungal ecological guilds did not change with forest age and ectomycorrhizal exploratory types were not good predictors of community dynamics. Our results suggest that the stand age effect on community composition may be driven by changes in nutrient supply provided by plant hosts to root-associated fungi.

Warming and nutrient-depleted food: Two difficult challenges faced simultaneously by an aquatic shredder

Global warming and changes in nutrient supply can alter the functioning of headwater stream ecosystems, where leaf-shredding invertebrates are pivotal for the transfer of nutrients through the food web. However, little is known about how warming and nutrient-depleted leaf litter interact and potentially exacerbate the already large elemental imbalance between shredders and their food. We hypothesized that: 1) shredders cannot increase their feeding rate to compensate for the effects of both factors simultaneously, and 2) shredders will increase assimilation efficiency of limiting nutrients, especially N, by decreasing excretion, increasing nutrient bioavailability in the gut, or both by adaptations of digestive enzymes. We performed a microcosms experiment with a caddisfly species subjected to 3 temperatures and 2 diets that differed in their N and P content. Overall, our results suggest that the combination of increasing temperatures and decreasing diet nutrient content lowered the capacity of larvae to acquire nutrients, either by decreasing nutrient assimilation, increasing nutrient excretion, or both. However, the trypsin enzyme maintained functionality under the range of temperatures we tested (5–15°C), which likely allows larvae to ensure N availability. Moreover, we detected reduced excretion and improved apparent assimilation of N relative to P. However, larval survival still decreased significantly at the highest temperature (15°C) when larvae were fed the low-nutrient diet. These results indicate that regulation mechanisms for reducing elemental constraints from poor food quality are less effective at higher temperatures. If these effects also occur in other detritivores, nutrient recycling and ecosystem function in headwater streams might be compromised as the climate warms.

Minimal cobalt metabolism in the marine cyanobacterium Prochlorococcus

Despite very low concentrations of cobalt in marine waters, cyanobacteria in the genus Prochlorococcus retain the genetic machinery for the synthesis and use of cobalt-bearing cofactors (cobalamins) in their genomes. We explore cobalt metabolism in a Prochlorococcus isolate from the equatorial Pacific Ocean (strain MIT9215) through a series of growth experiments under iron- and cobalt-limiting conditions. Metal uptake rates, quantitative proteomic measurements of cobalamin-dependent enzymes, and theoretical calculations all indicate that Prochlorococcus MIT9215 can sustain growth with less than 50 cobalt atoms per cell, ∼100-fold lower than minimum iron requirements for these cells (∼5,100 atoms per cell). Quantitative descriptions of Prochlorococcus cobalt limitation are used to interpret the cobalt distribution in the equatorial Pacific Ocean, where surface concentrations are among the lowest measured globally but Prochlorococcus biomass is high. A low minimum cobalt quota ensures that other nutrients, notably iron, will be exhausted before cobalt can be fully depleted, helping to explain the persistence of cobalt-dependent metabolism in marine cyanobacteria.

Biogeography of Macrophyte Elemental Composition: Spatiotemporal Modification of Species-Level Traits

The elemental composition of primary producers represents a potentially important pathway for linking ecosystem scale, climate-driven changes in nutrient supply to ecological processes at the population and community scales. However, such cross-scale linkages may also be dampened by conservation of species-specific differences in tissue stoichiometry. We investigated biogeographic patterns of elemental composition (%N, %C, and C:N ratio) of four ecologically dominant and functionally diverse marine intertidal macrophyte species (the brown algae Fucus distichus and Hedophyllum sessile, the red alga Mazzaella splendens, and the surfgrass Phyllospadix scouleri) along 900 km of coastline of the California Current System over a 10-year period. We used a nested hierarchical design to identify the dominant spatial and temporal scales of elemental composition variability and to test the sensitivity of macrophyte stoichiometry to changing ocean conditions in upwelling, the El Nino-Southern Oscillation (ENSO), the North Pacific Gyre Oscillation (NPGO), and the Pacific Decadal Oscillation (PDO). Elemental composition was highly conserved at the species level but was also sensitive to the environment, displaying marked species-dependent responses to spatial and temporal variation in ocean conditions. Moreover, the effects of local and seasonal processes were strong and with conserved species-specific differences, likely limited coherent cross-species sensitivity to climate variability from ENSO, NPGO and PDO. Unanticipated long-term steady increases in %C and bimodal increases in %N in brown algae and similar decreases in elemental composition of the red alga generated trimodal changes in C:N for these species. These changes may reflect responses of macrophyte communities to continuing changes in carbonate chemistry from ocean acidification.

The global effect of extreme weather events on nutrient supply: a superposed epoch analysis

To date, the effects of extreme weather events on nutrient supply within the population have not been quantified. In this study, we investigated micronutrient, macronutrient, and fibre supply changes during 175 extreme weather events within 87 countries in the year that a major extreme weather event occurred, with a targeted focus on low-income settings. We collected data from the International Disasters Database and the Global Expanded Nutrient Supply model for the period 1961-2010, and applied superposed epoch analysis to calculate the percentage change in nutrient supply during the year of an extreme weather event relative to its historical context. We composited globally and by subgroup (EU, landlocked developing countries, least developed countries, low-income food deficit countries, and net food-importing developing countries). Lastly, we reported nutrient supply changes in terms of recommended dietary allowance for children aged 1-3 years. Globally, all micronutrient supplies had a modest negative percentage change during the year of an extreme weather event; of these effects, those that reached an α=0·05 significance level included calcium, folate, thiamin, vitamin B6, and vitamin C, with nutrient supply changes ranging from -0·40 to -1·73% of the average supply. The effect of an extreme weather event was especially magnified among landlocked developing countries and low-income food deficit countries, with significant nutrient supply changes ranging from -1·61 to -7·57% of the average supply. Furthermore, the observed nutrient supply deficits in landlocked developing countries constituted a large percentage (ranging from 1·95 to 39·19%) of what a healthy child's sufficient average dietary intake should be. The global effects of extreme weather events on nutrient supply found in this study are modest in isolation; however, in the context of nutrient needs for healthy child development in low-income settings, the effects observed are substantial. Australian-American Fulbright Commission.

The Classification and Evolution of Bacterial Cross-Feeding

Bacterial feeding has evolved towards specific evolutionary niches and the sources of energy differ between species and strains. Although bacteria fundamentally compete for nutrients, the excreted products from one strain may be the preferred energy source or a source of essential nutrients for another strain. The large variability in feeding preferences between bacterial strains often provides for complex cross-feeding relationships between bacteria, particularly in complex environments such as the human lower gut, which impacts on the host’s digestion and nutrition. Although a large amount of information is available on cross-feeding between bacterial strains, it is important to consider the evolution of cross-feeding. Adaptation to environmental stimuli is a continuous process, thus understanding the evolution of microbial cross-feeding interactions allows us to determine the resilience of microbial populations to changes to this environment, such as changes in nutrient supply, and how new interactions might emerge in the future. In this review, we provide a framework of terminology dividing bacterial cross-feeding into four forms that can be used for the classification and analysis of cross-feeding dynamics. Under the proposed framework, we discuss the evolutionary origins for the four forms of cross-feeding and factors such as spatial structure that influence their emergence and subsequent persistence. This review draws from both the theoretical and experimental evolutionary literature to provide a cross-disciplinary perspective on the evolution of different types of cross-feeding.

Functional biogeography: Stoichiometry and thresholds for interpreting nutrient limitation in aquatic plants

Atmospheric N pollution may shift nutrient limitations in aquatic autotrophs from N to P or cause an intensification of P limitation in formerly pristine areas. Small changes in nutrient supply in oligotrophic lakes and rivers could lead to large changes in relative plant growth and yield with possible knock on effects on ecosystem carbon cycling through changes in the decomposition rate of their tissue. Previous biogeographical studies have shown inconsistent responses of plant nutrient tissue content and stoichiometry (functional traits) to external nutrient availability. Here we used a single species, Juncus bulbosus, to test the interplay between plant tissue nutrient (content and stoichiometry) and external environmental factors (local and catchment scale). We developed a comparative approach applicable globally to assess the thresholds for nutrient limitation in aquatic plants in the wild. Phosphorus in Juncus bulbosus tissue was negatively related to sediment organic matter (Fe root plaque limiting P uptake) and catchment vegetation cover (less P leaching to lakes). Our comparative approach revealed that the lack of increase in N plant tissue along the strong gradient in external N concentration may be explained by P limitation and strict plant tissue N:P ratio. Our comparative approach further showed that the nutrient content and stoichiometry of Juncus bulbosus was similar to other submerged aquatic plants growing in nutrient poor aquatic ecosystems. In southern Norway, mass development of Juncus bulbosus may be primarily triggered by changes in P availability, rather than CO2 or inorganic N, as previously thought, although co-limitations are also possible. If so, the mass development of Juncus bulbosus in oligotrophic aquatic ecosystems could be an early indicator of increasing P fluxes through these ecosystems which are less limited by N due to high atmospheric N deposition.