Variability and directionality of temporal changes in δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N of aquatic invertebrate primary consumers

Seasonal oscillations in the carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope signatures of aquatic algae can cause seasonal enrichment–depletion cycles in the isotopic composition of planktonic invertebrates (e.g., copepods). Yet, there is growing evidence that seasonal enrichment–depletion cycles also occur in the isotope signatures of larger invertebrate consumers, taxa used to define reference points in isotope-based trophic models (e.g., trophic baselines). To evaluate the general assumption of temporal stability in non-zooplankton aquatic invertebrates, δ¹³C and δ¹⁵N time series data from the literature were analyzed for seasonality and the influence of biotic (feeding group) and abiotic (trophic state, climate regime) factors on isotope temporal patterns. The amplitude of δ¹³C and δ¹⁵N enrichment–depletion cycles was negatively related to body size, although all size-classes of invertebrates displayed a winter-to-summer enrichment in δ¹³C and depletion in δ¹⁵N. Among feeding groups, periphytic grazers were more variable and displayed larger temporal changes in δ¹³C than detritivores. For nitrogen, temporal variability and magnitude of directional change of δ¹⁵N was most strongly related to ecosystem trophic state (eutrophic > mesotrophic, oligotrophic). This study provides evidence of seasonality in the isotopic composition of aquatic invertebrates across very broad geographical and ecological gradients as well as identifying factors that are likely to modulate the strength and variability of seasonality. These results emphasize the need for researchers to recognize the likelihood of temporal changes in non-zooplankton aquatic invertebrate consumers at time scales relevant to seasonal studies and, if present, to account for temporal dynamics in isotope trophic models.     

The trophic history of Myall Lakes,New South Wales,Australia: interpretations using δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N of the sedimentary record

In an attempt to determine the trophic history of the Myall Lakes complex (New South Wales, Australia) δ¹³C_org, δ¹⁵N and C_org:N profiles were determined for bulk organic matter of two short sediment cores from Bombah Broadwater and Myall Lake. ²¹⁰Pb profiles and sediment types indicate significantly different trophic trajectories during the time periods examined. δ¹³C_org and C_org:N indicate Bombah Broadwater has been dominated by increasing inputs of terrestrial organic material over the last century, thought to be related to watershed disturbance including agricultural activity. Primary production appears to be dominated by phytoplankton. δ¹⁵N remained relatively stable at around 1‰ until the mid–1970s when there was a sharp increase to 4.7‰, interpreted as an influx of sewage-derived material. These observations offer an insight into the recent trophic changes at the site. Sedimentation rates are noticeably lower in Myall Lake and the most recent sediment is a flocculent organic rich deposit overlying mineral clay. δ¹³C_org and C_org:N values indicate a transition from plankton to macrophyte dominated primary production around 1800AD. δ¹⁵N values become increasingly negative from approximately 1900AD. This is interpreted as being due to increasing reliance by macrophytes on nitrogen recycled from decomposing sediments driven by natural infilling and eutrophication in this basin. The contrasting sedimentation rates, sediment types and geochemical profiles suggest the different basins of this water body are subject to substantially different internal and external influences which should be considered in management decisions.     

Variation in δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N trophic enrichment factors among <Emphasis Type="Italic">Hyalella azteca</Emphasis> amphipods from different lakes

Stable isotopes are a powerful tool used to study the diets of animals because they provide information on food assimilated over an extended period. However, trophic enrichment factors used to reconstruct diets sometimes vary substantially, even among animals from the same trophic level. The goal of this study was to verify if trophic enrichment factors vary among animals as similar as Hyalella azteca amphipods from different lakes. We compared the carbon and nitrogen isotopic compositions of amphipods from different lakes fed on leaf detritus and on periphyton. Amphipods showed significant differences in their trophic enrichment factors among treatments (about 3.0‰ for carbon and nitrogen). The trophic enrichment factor of carbon was more affected by the food type, whereas the trophic enrichment factor of nitrogen was more affected by lake of origin. We estimated that amphipods had a tissue turnover of 25 days for carbon and 34 days for nitrogen. Our study showed that animals from different lakes can exhibit substantial variation in their trophic enrichment factors. This strengthens the view that trophic enrichment factors specific to a study system should be used whenever possible to reconstruct the in situ diet of consumers.     

Regional-scale patterns of δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N associated with multiple ecosystem functions along an aridity gradient in grassland ecosystems

Background and aims

Nitrogen (N) deficiency and drought are two key limiting factors for rice production worldwide, but the relationship of drought stress with N homeostasis in rice is rarely advanced. The aim of this study was to dissect the physiological effects of drought stress on rice growth that coupled unbalanced N metabolism.

Results

Water-deficient stress (WD) limited stomatal aperture function and activity of Rubisco carboxylase to photosynthesis. The rate of total electron transport (J_t) and the electron to carboxylation (J_c) were considerably decreased, whereas the proportion of e^? flow to photorespiration was stimulated by WD, especially at 1600 μmol m^?2 s^?1 PPFD. Concurrently, the expressions of glycolate oxidase genes (GOX1, GOX5) and glycine decarboxylase complex (GDCH, GDCP and GDCT) were significantly induced in leaves of WD treatment, which led to the accumulation of reactive oxygen species in leaves. With the photosynthetic change, nitrate uptake and reduction were suppressed. Moreover, the enhanced photorespiration generated excess NH₃ accumulation in leaves and stimulated the expressions of GS1;1, GS1;2 and GS2, which were tightly coupled with the expressions of PEPC1 and PEPC2 under WD stress.

Conclusions

Our results suggest that the inhibited nitrate reduction associated with diminished electron transport rate, and the photorespiration-associated accumulation of hydrogen peroxide and NH₃ were critical in the drought-induced rice growth inhibition.

     

Structures and stability of N<Subscript>13</Subscript><Superscript>+</Superscript> and N<Subscript>13</Subscript><Superscript>−</Superscript> clusters

The structures and stabilities of eleven N₁₃ ⁺ and N₁₃ ^– isomers have been investigated with second-order Møller–Plesset (MP2) and density functional theory (DFT) methods. Five N₁₃ ⁺ isomers and six N₁₃ ^– isomers are all reasonable local minima on their potential energy hypersurfaces. The most stable N₁₃ ⁺ cation is structure C-2 with C_2v symmetry, which contains a pentazole ring and two N₄ open chains. It is different from those of the N₇ ⁺ and N₉ ⁺ clusters, but similar to the N₁₁ ⁺ cluster. Meanwhile, the most stable N₁₃ ^– structure A-2 is composed of a pentazole ring and a six-membered ring connected by two nitrogen atoms. It is not only different from those of the N₇ ^– and N₉ ^– clusters, but also from the N₁₁ ^– cluster. The decomposition pathways of structures C-2 and A-2 were investigated at the B3LYP/(aug)-cc-pVDZ level. From the barrier heights of the structures C-2 and A-2 decomposition processes, it is suggested that C-2 is difficult to observe experimentally and A-2 may be observed as a short-lived species. Figure Optimized geometrical parameters of N₁₃ ⁺ isomer C-2      

Determination of the lifetime of D<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and HD<Superscript>−</Superscript> ions

A method for determining the lifetime of unstable ions is described. The method is based on measuring the decrease in the ion beam current onto a fixed detector with increasing path length of the ion beam from the ion source to the detector. The measurements performed for D^? ₂ and HD^? molecular ions have shown that their lifetimes are 3.5 ± 0.1 and 4.4 ± 0.1 μs, respectively.     

Spatial variation in flux, δ<Superscript>13</Superscript>C and δ<Superscript>2</Superscript>H of methane in a small Arctic lake with fringing wetland in western Greenland

Small lakes in northern latitudes represent a significant source of CH₄ to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH₄ budgets are lacking as are measurements of δ¹³C-CH₄ and δ²H-CH₄. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH₄ and corresponding δ¹³C-CH₄ and δ²H-CH₄ in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH₄ flux was highly variable, ranging from an average flux of 7 mg CH₄ m^?2 d^?1 in the deep-water zone to 154 mg CH₄ m^?2 d^?1 along the lake margin. Diffusive flux accounted for ~8.5 % of mean net CH₄ flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean ± SD 10 ± 17 %) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH₄ emissions varied widely throughout the system, with δ¹³C-CH₄ ranging from ?66.2 to ?55.5 ‰, and δ²H-CH₄ ranging from ?345 to ?258 ‰. Carbon isotope composition of CH₄ in ebullitive flux showed wider variation compared to net flux, ranging from ?69.2 to ?49.2 ‰. Dissolved CH₄ concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH₄ in the hypoxic deep water coincided with decreasing dissolved O₂ concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ¹³C-CH₄ and δ²H-CH₄. The most depleted ¹³C- and ²H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ¹³C and δ²H observations of CH₄, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH₄ in deeper sediments were consistent with mixing/transition between CH₄ production pathways, indicating a higher contribution of the CO₂ reduction pathway. The large spatial variability in fluxes of CH₄ and in isotopic composition of CH₄ throughout a single lake system indicates that the underlying mechanisms controlling CH₄ cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH₄ emissions in these systems. Future studies of whole-lake CH₄ budgets should consider this significant spatial heterogeneity.     

Effects of salt water immersion caused by a tsunami on δ<Superscript>13</Superscript>C and δ<Superscript>18</Superscript>O values of <Emphasis Type="Italic">Pinus thunbergii</Emphasis> tree-ring cellulose

Pinus thunbergii trees growing on Pacific coastal sand dunes in Japan were immersed by the tsunami that followed the Great East Japan Earthquake on 11 March 2011. Even trees that survived direct physical damage began to die during the following summer, probably because of the physiological stress of salt water immersion. The objectives of this study were to analyze the relationship between the carbon and oxygen isotope values (δ¹³C and δ¹⁸O, respectively) of P. thunbergii tree-ring cellulose and the effects of salt water immersion caused by the tsunami. Pinus thunbergii trees were sampled in Yamamoto, Miyagi Prefecture, and in Misawa, Aomori Prefecture. Each tree-ring that formed between 2008 and 2012 was sliced into four to eight equal subdivisions, and the isotope values were analyzed at a high time-scale resolution. Tree rings that were immersed in seawater from the tsunami had higher δ¹³C values in the earlywood that formed in the spring following the tsunami than those formed prior to the disaster. This increase in δ¹³C values was likely caused by osmotic stress from root immersion in salt water. We did not observe a clear change in tree-ring δ¹⁸O values after the tsunami. This lack of variance might have resulted from the post-photosynthetic exchange of carbonyl oxygens with non-¹⁸O-enriched xylem water.     

Nutrient cycling relative to δ<Superscript>15</Superscript>N and δ<Superscript>13</Superscript>C natural abundance in a coastal wetland with long-term nutrient additions

Because nitrogen and phosphorus are primary resources for plant, algal, and microbial production, increases in nutrient inputs can markedly alter aquatic ecosystems. Coastal wetland plots at Belle W. Baruch Marine Field Laboratory (South Carolina, USA) have been amended with nitrogen and phosphorus for ~20 years to determine the effects of nutrient loading on coastal wetlands. We conducted a survey of δ¹⁵N and δ¹³C natural abundance in coastal wetland organic pools (sediment, vegetation) with long-term nutrient amendments (control, no addition; nitrogen; phosphorus; and nitrogen + phosphorus additions). Additionally, we conducted laboratory assays to quantify pore water nutrient availability and nitrification rates. Marsh vegetation (Spartina alterniflora) had enriched δ¹³C values (mean −14‰) relative to bulk sediment samples (mean −18‰). Nitrogen-amended plots (alone and in combination with phosphorus) had enriched δ¹³C values in the surface sediment (0–5 cm; mean −16.1‰) relative to control (mean −16.5‰) and phosphorus-amended plots (mean −16.8‰). Nitrogen-amended plots also had depleted δ¹⁵N in S. alterniflora leaf tissues (−3.3‰) and surface sediment samples (mean 2.1‰) relative to leaf tissues (mean 2.1‰) or sediment samples (mean 5.8‰) from control or phosphorus-only amended plots. Nitrate availability (as increased pore water concentration) was higher in N-amended plots although ammonium availability did not differ. Phosphorus availability was higher only in phosphorus-only amended plots. Overall, we found that long-term nutrient amendments to coastal wetlands significantly altered nutrient availability and uptake rates as well as natural abundance of δ¹³C and δ¹⁵N in multiple organic matter sources.     

Estimation of denitrification potential in a karst aquifer using the <Superscript>15</Superscript>N and <Superscript>18</Superscript>O isotopes of NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>

A confined aquifer in the Malm Karst of the Franconian Alb, South Germany was investigated in order to understand the role of the vadose zone in denitrifiaction processes. The concentrations of chemical tracers Sr²⁺ and Cl^– and concentrations of stable isotope ¹⁸O were measured in spring water and precipitation during storm events. Based on these measurements a conceptual model for runoff was constructed. The results indicate that pre-event water, already stored in the system at the beginning of the event, flows downslope on vertical and lateral preferential flow paths. Chemical tracers used in a mixing model for hydrograph separation have shown that the pre-event water contribution is up to 30%. Applying this information to a conceptual runoff generation model, the values of ¹⁵N and ¹⁸O in nitrate could be calculated. Field observations showed the occurence of significant microbial denitrification processes above the soil/bedrock interface before nitrate percolates through to the deeper horizon of the vadose zone. The source of nitrate could be determined and denitrification processes were calculated. Assuming that the nitrate reduction follows a Rayleigh process one could approximate a nitrate input concentration of about 170 mg/l and a residual nitrate concentration of only about 15%. The results of the chemical and isotopic tracers postulate fertilizers as nitrate source with some influence of atmospheric nitrate. The combined application of hydrograph separation and determination of isotope values in ¹⁵N and ¹⁸O of nitrate lead to an improved understanding of microbial processes (nitrification, denitrification) in dynamic systems.     

A critical evaluation of intrapopulation variation of δ<Superscript>13</Superscript>C and isotopic evidence of individual specialization

Individual variation in the diet of consumers is common in many ecological systems and has important implications for the study of population dynamics, animal behavior, and evolutionary or ecological interactions. Ecologists frequently quantify the niche of a population by intensive analyses of gut contents and feeding behaviors of consumers. Inter-individual differences in ¹³C signature can indicate long term differences in feeding behavior, often unattainable by a single snapshot analysis of gut contents. If a consumers food sources have unique ¹³C signatures, then the intrapopulation variation in ¹³C may be useful for quantifying diet variation and detecting isotopic evidence of individual specialization. However, intrapopulation variation in ¹³C can underestimate or overestimate dietary variation, and therefore is not directly equivalent to a dietary based niche. In this paper we show that intrapopulation variability of ¹³C in consumers critically depends on the isotopic range and distribution of food sources. Our analyses fundamentally challenge how we interpret the intrapopulation isotopic variance of ¹³C, and how we evaluate isotopic evidence of individual specialization.     

Flow of Deposited Inorganic N in Two Gleysol-dominated Mountain Catchments Traced with <Superscript>15</Superscript>NO<Subscript>3</Subscript><Superscript>−</Superscript> and <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript>

In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of ¹⁵NO₃ and ¹⁵NH₄ were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately 1600 m², were delimited by trenches in the Gleysols. K¹⁵NO₃ was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition. After the sampling and a one-year break, ¹⁵NH₄Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood), ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period, the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO₃⁻ than NH₄⁺ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of ¹⁵NO₃⁻ in runoff, with sharp ¹⁵N peaks corresponding to discharge peaks. NO₃⁻ leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline of its C:N ratio.     

Can tree-ring δ<Superscript>15</Superscript>N be used as a proxy for foliar δ<Superscript>15</Superscript>N in European beech and Norway spruce?

Key message

For long-term environmental investigations, tree-ring δ ¹⁵ N values are inappropriate proxies for foliar δ ¹⁵ N for both Fagus sylvatica and Picea abies under moderate N loads.

Abstract

Currently it is unclear whether stable nitrogen isotope signals of tree-rings are related to those in foliage, and whether they can be used to infer tree responses to environmental changes. We studied foliar and tree-ring nitrogen (δ¹⁵N) and carbon (δ¹³C) isotope ratios in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies L.) from six long-term forest monitoring sites in Switzerland together with data on N deposition and soil N availability, as well as a drought response index over the last two decades. For both species, tree-ring δ¹⁵N and δ¹³C values were less negative compared to foliar δ¹⁵N and δ¹³C values, most likely due to recycling and reallocation of N within the tree and fractionation processes associated with the transport of sucrose and the formation of tree-rings, respectively. Temporal trends recorded in foliar δ¹⁵N were not reflected in tree-ring δ¹⁵N, with much higher variations in tree-rings compared to foliage. Soil N availability and N deposition were partially able to explain changes in foliar δ¹³C, while there were no significant correlations between environmental variables and either tree-ring or foliar δ¹⁵N. Our results suggest an uncoupling between the N isotopic composition of tree-rings and foliage. Consequently, tree-ring δ¹⁵N values are inappropriate proxies of foliar δ¹⁵N values under low-to-moderate N deposition loads. Furthermore, at such low levels of deposition, tree-ring δ¹⁵N values are not recommended as archives of tree responses to soil C/N or bulk N deposition.

     

The influence of weed control on foliar δ<Superscript>15</Superscript>N, δ<Superscript>13</Superscript>C and tree growth in an 8 year-old exotic pine plantation of subtropical Australia

Background and aims

The aim of weed control and fertilization in forest plantations was to increase tree growth by reducing competition for available nutrients and water. However, treatments that influence weed biomass can also have significant impacts on soil carbon (C) and nitrogen (N) cycling which can in turn lead to changes in the dynamics of stable C (δ¹³C) and N (δ¹⁵N) isotope compositions in soils and tree foliage.

Methods

We examined the key C and N cycling processes influenced by routine and luxury weed control and fertilization treatments as reflected by soil and foliar δ¹³C and δ¹⁵N and long-term tree growth in an 8-year old F₁ hybrid pine (Pinus elliottii x P. caribaea) plantation in southeast Queensland, Australia. Weed control treatments varied by treatment frequency and intensity while fertilization treatments varied by the application of N, phosphorus (P), potassium (K) and micronutrients. Different soil and canopy sampling positions were assessed to determine if sampling position enhanced the relationships among soil N transformations and tree N use, water use efficiency and carbon gain under the early establishment silviculture.

Results

Routine weed control was associated with increased weed biomass returned to the soil, compared with luxury weed control. Soil δ¹³C increased at the 0–5 cm soil sampling depth in both the inter-planting (IPR) and planting row (PR) as a result of the routine weed control treatments. In addition, soil δ¹³C was significantly higher as a result of fertilisation treatment in the 0–5 cm soil sampling depth in the PR. Soil δ¹³C was negatively correlated to soil δ¹⁵N at the 0–5 cm soil sampling depth in the IPR. Soil δ¹⁵N increased in the 0–5 and 5–10 cm soil sampling depths in the IPR, as a result of more frequent (luxury) weed control. Foliar δ¹⁵N and tree water use efficiency (WUE) (as indicated by foliar δ¹³C) were positively correlated with tree growth at age 8 years. While relationships between δ¹³C and δ¹⁵N in the soil and foliage varied depending on soil sampling depth and position, and with canopy sampling position where there were consistent relationships between soil δ¹³C (or δ¹⁵N) and foliar δ¹⁵N.

Conclusions

This study demonstrates how early establishment silviculture has important implications for soil C and N cycling and how soil δ¹³C and δ¹⁵N were consistent with changes in soil C cycling and N transformations as a result of weed control treatments, while foliar δ¹⁵N was linked to more rapid N cycling as reflected in the soil δ¹⁵N, which increased tree growth and tree WUE (as reflected by foliar δ¹³C).

     

Synthesis of the β-amyloid fragment <Superscript>5</Superscript>RHDSGY<Superscript>10</Superscript> and its isomers

The peptide RHDSGY, a fragment of the human β-amyloid Zn-binding site, and its isomers RH(D-Asp)SGY and RH(β-Asp)SGY have been obtained as amides by means of solid-phase synthesis and analyzed by HPLC and various mass spectrometric methods. The problem of low yield of the RHDSGY peptide and its isomers attributed to 9-fluorenylmethoxycarbonyl (Fmoc)-amino acids and/or formation of such side-products as RH(β-Asp)SGY (or RHDSGY during synthesis of RH(β-Asp)SGY) and RH(Asp-imide) SGY was solved via selection of individual reagents for removal of Fmoc groups from α-amino groups of the growing peptide chain.     

CD14<Superscript>++</Superscript>CD16<Superscript>−</Superscript> and CD14<Superscript>+</Superscript>CD16<Superscript>+</Superscript> human monocyte adhesion to endothelial cells

Based on the difference in the CD14 and CD16 expression, two subsets of monocytes were identified in human and other mammalian blood. These subsets have different patterns of adhesion molecules and chemokine receptors that suggests the different mode of their interaction with endothelium and tissue traffic. Here, we investigated the ability of CD14⁺CD16⁺ and CD14⁺⁺CD16⁻ monocytes to adhere to endothelial cell monolayer in presence or absence of pro- and anti-inflammatory cytokines. We demonstrated that CD14⁺CD16⁺ monocytes had a higher level of adhesion to intact monolayer of endothelial cells than CD14⁺⁺CD16⁻ monocytes. Adhesion of CD14⁺⁺CD16⁻ and CD14⁺CD16⁺ monocytes significantly increased in the presence of TNFα or its combination with other cytokines. IFNγ and IL-4 alone did not affect the adhesion of monocytes. These results show that CD14⁺⁺CD16⁻ and CD14⁺CD16⁺ monocytes can be recruited to the inflamed endothelium, but CD14⁺CD16⁺ monocytes adhere to endothelial cells without inflammations twice as strongly as CD14⁺⁺CD16⁻ monocytes.     

δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N in tissue of coral polyps and epilithic algae inhabiting damaged coral colonies under the influence of different light intensities

Studies were performed of the carbon and nitrogen stable isotope (δ¹³C and δ¹⁵N) composition (δ¹³C and δ¹⁵N) of the corals Porites cylindrica and P. lutea (5 years after damaging the colonies by the bleaching events) and of epilithic algae settled onto damaged areas of coral colonies. Coral polyps and three epilithic algal communities (‘red algal turf, green algal turf and red calcified crusts’) were sampled along the boundary between communities of coral polyps and algal colonizers from differently illuminated habitats from 2 to 90% of incident surface photosynthetically active radiation (PAR₀). It was found that communities with a predominance of red algae significantly differed from communities with a predominance of green algae in δ¹³C but not in δ¹⁵N values. An influence of habitat irradiance was found only for communities of coral polyps for δ¹³C and δ¹⁵N values: under bright light (70–90% PAR₀) polyp tissues of both coral species were significantly enriched in heavy carbon isotopes and insignificantly in nitrogen isotopes (δ¹³C values difference ~4‰) relative to tissues of corals under lower light 15–50% PAR₀. On the basis of these results we assumed that differences in light intensities in the habitat ranging from 15 to 90% PAR₀ do not influence on accessibility of the main carbon and nitrogen sources for corals and algae, and exchange by these elements between organisms. We also assumed that the relative enrichment in the heavy carbon isotopes of coral tissues in high light is a result of decreased isotope fractionation (or the absence of fractionation in photosynthesis of their zooxanthellae).     

Evaluating the need for acid treatment prior to δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N analysis of freshwater fish scales: effects of varying scale mineral content,lake productivity and CO<Subscript>2</Subscript> concentration

In order to evaluate the need for using scale acidification to remove carbonates prior to stable isotope analysis, we compared acidified and non-acidified scales of six freshwater fish species (perch, roach, rudd, pike, tench and bream) with contrasting mineral content in their scales. Fish samples were taken from six lakes with variable trophic conditions, ranging from oligotrophic to hypertrophic, and differing in CO₂ concentrations. The scale mineral content of the six species studied ranged between 31.8 and 61.3% dry weight (DW) in tench and perch, respectively. The elemental composition was characterised by high amounts of phosphorus, varying from 4.5 to 9.1% DW. The mineral fraction was dominated by apatite (range 24.4–49.2% DW), carbonates constituted a very small proportion of the total carbon content (average ± SD: 5.5 ± 1.7%). The average effect of acidification was very small for all species (average ± SD: 0.181 ± 0.122 and −0.208 ± 0.243 for carbon and nitrogen, respectively), albeit significant for five out of the six species (excepting tench that had the lowest mineral content). Linear regression slopes between acidified and untreated scales did not differ significantly from one for almost all the species and isotopes. The effects of acidification on the two isotopes were correlated with the relative carbonate content as well as with the CO₂ concentration for carbon and total phosphorus for nitrogen. We conclude that the need for scale acidification depends on the different species and on the system studied, although in most cases the acidification effect will be biologically irrelevant. However, dual analysis of acidified and untreated scales may provide useful information on differences in stable isotope composition of dissolved inorganic carbon and on phytoplankton carbon fractionation generated by varying levels of CO₂ availability.     

Sequence specific <Superscript>1</Superscript>H, <Superscript>13</Superscript>C and <Superscript>15</Superscript>N resonance assignments of a cataract-related variant G57W of human γS-crystallin

γS-crystallin is a major structural component of the human eye lens, which maintains its stability over the lifetime of an organism with negligible turnover. The G57W mutant of human γS-crystallin (abbreviated hereafter as γS-G57W) is associated with dominant congenital cataracts. In order to provide a structural basis for the ability of γS-G57W causing cataract, we have cloned, overexpressed, isolated and purified the protein. The 2D [¹⁵N–¹H]-HSQC spectrum recorded with uniformly ¹³C/¹⁵N-labelled γS-G57W was highly dispersed indicating the protein to adopt an ordered conformation. In this paper, we report almost complete sequence-specific ¹H, ¹³C and ¹⁵N resonance assignments of γS-G57W using a suite of heteronuclear 3D NMR experiments.