The nitrogen isotopic composition (δ 15 N) of amino acids is potentially useful as an alternative method for estimating the trophic levels of organisms in food webs. However, because this "amino acid method" has been constructed from the observations of only a few case studies of food-consumer combinations in previous studies, the universality of the approach remains unclear. In this study, we investigated the δ 15 N signatures of amino acids in 17 photoautotrophs and the trophic relationships during four controlled feeding experiments using green algae, zooplankton, and fish. The results are consistent with those reported in previous studies, implying that the amino acid method can be applied to a variety of organisms. From these and previously published data, we estimate the two factors (β, isotope differences among amino acids in primary producers; Δ, the 15 N-enrichment factor for each trophic level) required to calculate the trophic level. Based on the lowest error (1σ = 0.12) in the estimated trophic level, we conclude that a comparison of the δ 15 N values for glutamic acid and phenylalanine is most useful in calculating precise estimates of the trophic level, using the following equation: trophic level (TL Glu/Phe ) = (δ 15 N Glu -δ 15 N Phe -3.4)/7.6 + 1.

We investigated the nitrogen isotopic compositions of individual amino acids from brown and red macroalgae and gastropods in a natural marine coastal environment, to further evaluate them as a tool for ecological studies and to understand the factor(s) controlling the isotopic compositions in terms of biosynthetic and metabolic processes. The isotopic compositions of 12 amino acids range from -2.1 to + 8.4 ‰ for brown algae, from -3.3 to +12.9 ‰ for red algae, and from -0.6 to +16.6 ‰ for gastropods. The isotopic distributions between algae and gastropods and within algal classes are consistent with those in previous reports, suggesting them to be quite useful for studying food web structure. The nitrogen isotopic variation between amino acids strongly reflects their biosynthetic and metabolic processes. In particular, we suggest here that metabolic fate is an important factor in producing distinct trophic relationships in nitrogen isotopic compositions between amino acids. KEY WORDS: Nitrogen isotopic composition · Amino acids · Food web · Trophic level · Biosynthesis Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 342: [85][86][87][88][89][90] 2007 nation is generally applicable to other sets of producers and consumers. Particularly, few other data are available for primary producers, even though they provide essential information on the base of the food web. Moreover, the biochemical mechanism responsible for the distinct trophic relationship of δ 15 N value between amino acids (i.e. significant 15 N-enrichment in some amino acids vs. little change in others) is not well understood. Therefore, in the present study, we investigated the nitrogen isotopic compositions of individual amino acids in natural marine macroalgae and gastropods: (1) to ascertain the trophic relationship of the δ 15 N of amino acids in a marine coastal ecosystem and (2) to discuss controlling factor(s) of the isotopic signature of each amino acid from both biosynthetic and metabolic viewpoints. MATERIALS AND METHODSTwo brown (Heterokontophyta: Sargassum filicinum and Undaria pinnatifida) and 2 red (Rhodophyta: Binghamia californica and Gelidium japonica) macroalgae were collected from 2 to 4 m depth along the seacoast near Yokohama, Japan (35°08' N, 139°07' E) (Chikaraishi 2006). About 20 to 30 ind. for each alga were collected. This area is dominated by the brown algae and small colonies of the red algae, which are found in the vicinity of the brown algal colonies; other macroalgae are not common in this coastal area. We also collected 3 gastropods (Gastropoda: Batillus cornutus, Haliotis discus, and Omphalius pfeifferi) from the brown algal colonies. One individual from each gastropod species was collected. It has been shown that these gastropods specifically feed on brown macroalgae (e.g. Harada et al. 1984, Tutschulte & Connell 1988, Fallu 1991. This was also confirmed in this environment by a previous investigation into the carbon and hydrogen isotopic compositions of ster...

A deep sleep in coal beds Deep below the ocean floor, microorganisms from forest soils continue to thrive. Inagaki et al. analyzed the microbial communities in several drill cores off the coast of Japan, some sampling more than 2 km below the seafloor (see the Perspective by Huber). Although cell counts decreased with depth, deep coal beds harbored active communities of methanogenic bacteria. These communities were more similar to those found in forest soils than in other deep marine sediments. Science , this issue p. 420 ; see also p. 376

Food webs are known to have myriad trophic links between resource and consumer species. While herbivores have well-understood trophic tendencies, the difficulties associated with characterizing the trophic positions of higher-order consumers have remained a major problem in food web ecology. To better understand trophic linkages in food webs, analysis of the stable nitrogen isotopic composition of amino acids has been introduced as a potential means of providing accurate trophic position estimates. In the present study, we employ this method to estimate the trophic positions of 200 free-roaming organisms, representing 39 species in coastal marine (a stony shore) and 38 species in terrestrial (a fruit farm) environments. Based on the trophic positions from the isotopic composition of amino acids, we are able to resolve the trophic structure of these complex food webs. Our approach reveals a high degree of trophic omnivory (i.e., noninteger trophic positions) among carnivorous species such as marine fish and terrestrial hornets.This information not only clarifies the trophic tendencies of species within their respective communities, but also suggests that trophic omnivory may be common in these webs.

Compound-specific isotopic analysis of amino acids (CSIA-AA) has emerged in the last decade as a powerful approach for tracing the origins and fate of nitrogen in ecological and biogeochemical studies. This approach is based on the empirical knowledge that source AAs (i.e., phenylalanine), fractionate 15 N very little (<0.5‰) during trophic transfer, whereas trophic AAs (i.e., glutamic acid), are greatly (~6-8‰) enriched in 15 N during each trophic step. The differential fractionation of these two AA groups can provide a valuable estimate of consumer trophic position that is internally indexed to the baseline δ 15 N value of the integrated food web. In this paper, we critically review the analytical methods for determining the nitrogen isotopic composition of AAs by gas chromatography/isotope-ratio mass spectrometry. We also discuss methodological considerations for accurate trophic position assessment of organisms using CSIA-AA. We then discuss the advantages and challenges of the CSIA-AA approach by examining published studies including trophic position assessment in various ecosystems, reconstruction of ancient human diets, reconstruction of animal migration and environmental variability, and assessment of marine organic matter dynamics. It is clear that the CSIA-AA approach can provide unique insight into the sources, cycling, and trophic modification of organic nitrogen as it flows through systems. However, some uncertainty still exists in how biochemical, physiological, and ecological mechanisms affect isotopic fractionation of trophic AAs. We end this review with a call for continued exploration of the mechanisms of AA isotopic fractionation, through various studies to promote the evolution of the rapidly growing field of CSIA-AA.

The Early Cretaceous Ontong Java Plateau was emplaced at almost the same time as marine biotic changes that culminated in oceanic anoxic event 1 (OAE1a). A causative link between these events has been suggested, but direct evidence has been lacking until now. New Os isotope measurements across the Lower Aptian "Selli Level" black shale deposited during OAE1a in central Italy reveal two negative excursions in marine 187 Os/ 188 Os ratios within a period of 2 Ma starting above the Barremian-Aptian boundary and ending just above the Selli Level horizon, suggesting an order-of-magnitude increase in the global fl ux of unradiogenic Os. The results are consistent with early and major phases of eruption of the Ontong Java Plateau. The latter phase is estimated to have been as short as ~1 Ma and may have induced widespread oceanic stratifi cation that triggered OAE1a.

[1] Isotopomer ratios of N 2 O (bulk nitrogen and oxygen isotope ratios, d 15 N bulk and d 18 O, and intramolecular 15 N site preference, SP) are useful parameters that characterize sources of this greenhouse gas and also provide insight into production and consumption mechanisms. We measured isotopomer ratios of N 2 O emitted from typical Japanese agricultural soils (Fluvisols and Andisols) planted with rice, wheat, soybean, and vegetables, and treated with synthetic (urea or ammonium) and organic (poultry manure) fertilizers. The results were analyzed using a previously reported isotopomeric N 2 O signature produced by nitrifying/denitrifying bacteria and a characteristic relationship between d 15 N bulk and SP during N 2 O reduction by denitrifying bacteria. Relative contributions from nitrification (hydroxylamine oxidation) and denitrification (nitrite reduction) to gross N 2 O production deduced from the analysis depended on soil type and fertilizer. The contribution from nitrification was relatively high (40%-70%) in Andisols amended with synthetic ammonium fertilizer, while denitrification was dominant (50%-90%) in the same soils amended with poultry manure during the period when N 2 O production occurred in the surface layer. This information on production processes is in accordance with that obtained from flux/concentration analysis of N 2 O and soil inorganic nitrogen. However, isotopomer analysis further revealed that partial reduction of N 2 O was pronounced in high-bulk density, alluvial soil (Fluvisol) compared to low-bulk density, volcanic ash soil (Andisol), and that the observed difference in N 2 O flux between normal and pelleted manure could have resulted from a similar mechanism with different rates of gross production and gross consumption. The isotopomeric analysis is based on data from pure culture bacteria and would be improved by further studies on in situ biological processes in soils including those by fungi. When flux/concentration-weighted average isotopomer ratios of N 2 O from various fertilized soils were examined, linear correlations were found between d 15 N bulk and d 18 O, and between SP and d 15 N bulk . These relationships would be useful to parameterize isotopomer ratios of soil-emitted N 2 O for the modeling of the global N 2 O isotopomer budget. The results obtained in this study and those from previous firn/ice core studies confirm that the principal source of anthropogenic N 2 O is fertilized soils.Citation: Toyoda, S., et al. (2011), Characterization and production and consumption processes of N 2 O emitted from temperate agricultural soils determined via isotopomer ratio analysis, Global Biogeochem. Cycles, 25, GB2008,

Food web ecologists have long sought to characterize the trophic niches of animals using stable isotopic analysis. However, distilling trophic position from isotopic composition has been difficult, largely because of the variability associated with trophic discrimination factors (inter-trophic isotopic fractionation and routing). We circumvented much of this variability using compound-specific isotopic analysis (CSIA). We examined the 15N signatures of amino acids extracted from organisms reared in pure culture at four discrete trophic levels, across two model communities. We calculated the degree of enrichment at each trophic level and found there was a consistent trophic discrimination factor (~7.6‰). The constancy of the CSIA-derived discrimination factor permitted unprecedented accuracy in the measurement of animal trophic position. Conversely, trophic position estimates generated via bulk-15N analysis significantly underestimated trophic position, particularly among higher-order consumers. We then examined the trophic hierarchy of a free-roaming arthropod community, revealing the highest trophic position (5.07) and longest food chain ever reported using CSIA. High accuracy in trophic position estimation brings trophic function into sharper focus, providing greater resolution to the analysis of food webs.