Stable isotope ratios and uric acid preservation in termites belonging to three feeding habits in Thailand

Nitrogen and carbon stable isotope ratios and uric acid concentrations in termites sampled from a dry evergreen forest in Thailand, were determined across three kinds of feeding habits. Feeding habits of Microcerotermes crassus, which is an abundant wood-feeder, and Dicuspiditermes makhamensis, a common soil-feeding termite, were confirmed by isotopic signatures. Lichen feeding termites (Hospitalitermes birmanicus, H. bicolor and H. ataramensis) were characterized by low delta15N values, suggesting that they assimilated nitrogen deposited from the atmosphere. There was also a significant difference in uric acid concentrations between termites representing different feeding habits. No significant relationships were found between uric acid concentrations and delta15N or delta13C in Hospitalitermes. However, delta15N values were correlated with C/N ratios in H. birmanicus, except in one colony of H. ataramensis. delta13C values in both species were negatively correlated with C/N ratios.     

Nitrogen stable isotopes reveal age-dependent dietary shift in the Japanese scallop Mizuhopecten yessoensis

Ontogenetic niche shifts in diet are a consequence of changes in body size or resource partitioning between age classes. To better resolve the feeding patterns of the Japanese scallop Mizuhopecten yessoensis, we examined the relative importance of age and size in the diet of this species using stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) from 2006 to 2009. Contribution of food sources was quantified using an isotope mixing model by comparing the muscle tissue isotope ratios to those of suspended particulate organic matter (SPOM) and their zooplankton prey (e.g. micro- and meso-zooplankton). Unlike the δ¹³C values, which remained constant with age and size, muscle δ¹⁵N values were more positively correlated with age accounting for 69?% of variations than size with only 46?%. Increasing ¹⁵N values with age suggested that shifts in diet from SPOM to micro- and meso-zooplankton occurred during ontogeny in M. yessoensis. Results of the isotope mixing model indicated that SPOM contribution to scallop’s diet decreased from 68 to 8?% while those of zooplankton increased from 15 to 50?% with increasing age. This study concludes that age-related dietary shift explains the enrichment of ¹⁵N, as a result of predation on zooplankton by M. yessoensis.     

Carbon-13 Kinetic Isotope Effects in the Decarbonylation of Liquid Formic Acid Assisted with Acetic Anhydride

Abstract

We evaluated the use of δ¹⁵N- and δ¹³C-values to monitor the development of food web complexity and biodiversity in a regenerating ecosystem. Therefore a model food chain was established feeding cultivated woodlice (Porcellio dilatatus) on a cellulolytic fungus (Chaetomium globosum) grown on cellulose paper. Two diets of different quality (C:N ratios of 54 vs. 200) with different δ¹⁵N- (1.3‰ vs. 3.1‰) but identical δ¹³C-values caused low and high dietary stress in animals of treatment A and B, respectively. After an incubation time of 7 weeks amount, elemental and isotopic composition of collected faeces and exuviae as well as woodlice and remaining food were determined.

The increase of δ¹⁵N-values of woodlice relative to the diet was 5.7‰ and 2.5‰ in treatments A and B, respectively, whereas δ¹³C-shifts were 1.0‰ and 1.6‰, showing a reverse relationship. Modelling of elemental and isotopic mass balances indicated that faeces recycling explains the unexpected high ¹⁵N-enrichments. Moreover, ¹³C-enrichments were positively correlated to the degree of starvation. Considering the effects of starvation and recycling of faeces, stable isotopes represent a useful tool to elucidate trophic interactions in regenerating food webs.     

Nitrogen Isotope Ratios in Different Compartments of a Mixed Stand of Spruce,Larch and Beech Trees and of Understorey Vegetation Including Fungi

Abstract

Natural nitrogen isotope ratios were measured in different compartments (needles or leaves and twigs of different age classes and crown positions, roots and soil of different horizons) of spruce (Picea abies), larch (Larix decidua) and beech (Fagus sylvatica) trees in an 11-year-old mixed stand in the Fichtelgebirge, NE Bavaria, Germany. In addition, samples of understorey vegetation (mainly ericaceous shrubs and grass) and of ectomycorrhizal and saprophytic fungi were analyzed. The δ¹⁵N values found for all samples ranged between ?7.5 and + 4.5‰. No significant differences were found for the nitrogen isotope ratios of the three tree species despite of their evergreen versus deciduous foliage and despite of their different rooting depth. Ericaceous shrubs had the most negative and fungi and soil from the mineral horizon the most positive δ¹⁵N values. Positive δ¹⁵N values of the fungi indicate their ability to utilize organic soil nitrogen, but the data do not unequivocally show that plants forming mycorrhizas profit from this organic nitrogen source.     

Feeding and Growth of Apple Snail Pomacea lineata in the Pantanal Wetland,Brazil—a Stable Isotope Approach

Abstract

Apple snails Pomacea lineata (SPIX 1827) are widespread in the tropical regions of Brazil as well as in the Pantanal wetland of Mato Grosso in the western part of the country. They have a key position in the Pantanal food web and serve as food for many animals e.g. fishes, birds, and caimans. However, little is known about their feeding preferences and growth rates. Stable isotopes have been used successfully on numerous studies as food source indicator. Therefore, the δ¹⁵N and δ¹³C values of snails from 0.45 to 3.03cm in length, which were collected in the rainy season from March through May, were analyzed. Snails signatures revealed ambiguous evidence for food preferences. δ¹⁵N and δ¹³C values ranged between ?2.8 and 12.4‰ and between ?24.2 and ?16.4‰, respectively. This range of values mirrors the highly variable isotope values of possible food sources comprising C₃ and C₄ macrophytes. To test whether all common food sources were similarly assimilated, feeding experiments with different diets were conducted. Snail eggs were reared in tanks and offered different but single plants. Snails fed different diets and δ¹³C values of the food were reflected in the animal tissue. Growth varied considerably in experiments with different diets indicating the preference for certain food sources. Also, the fractionation of nitrogen isotopes between food and animal varied from 0.1 to 17.0‰. The results are explained by different feeding habits, and it is supposed that animals fed either on the plant itself or on bacteria mats growing in the tanks. In an additional experiment juvenile snails were offered one single food with a distinctive C₄ grass signature. These snails did not grow detectably, but nevertheless isotope signatures approached to values of the diet.     

Characteristics of suspended matter in the River Sava watershed,Slovenia

A combination of C/N ratios, δ¹³C and δ¹⁵N values in suspended matter was used to examine the seasonal (late summer 2004 and spring 2005) relationship with hydrological characteristics of the River Sava watershed in Slovenia. The values of C/N ratios range from 1.2 to 19.1, δ¹³C values range from?29.2 to?23.0 ‰ and δ¹⁵N values from 0.5 to 16.7 ‰ and indicate that the samples are a mixture of two end members: modern soils and plant litter. A simple mixing model was used to indicate that soil organic carbon prevails over plant litter and contributes more than 50% of suspended material. The calculated annual particulate organic carbon flux is estimated as 5.2×10¹⁰ g C/year, the annual particulate nitrogen flux 8.5×10⁹ g N/year and the total suspended solid flux is estimated to be 1.3×10¹² g/year. Anthropogenic impact was detected only in a tributary stream of the River Sava, which is located in an agriculture–industrial area and is reflected in higher δ¹⁵N values in suspended matter and high nitrate concentrations in the late summer season.     

Seasonal variation in natural abundance of δ13C and 15N in Salicornia brachiata Roxb. populations from a coastal area of India

High and fluctuating salinity is characteristic for coastal salt marshes, which strongly affect the physiology of halophytes consequently resulting in changes in stable isotope distribution. The natural abundance of stable isotopes (δ¹³C and δ¹⁵N) of the halophyte plant Salicornia brachiata and physico-chemical characteristics of soils were analysed in order to investigate the relationship of stable isotope distribution in different populations in a growing period in the coastal area of Gujarat, India. Aboveground and belowground biomass of S. brachiata was collected from six different populations at five times (September 2014, November 2014, January 2015, March 2015 and May 2015). The δ¹³C values in aboveground (?30.8 to ?23.6?‰, average: ?26.6?±?0.4?‰) and belowground biomass (?30.0 to ?23.1?‰, average: ?26.3?±?0.4?‰) were similar. The δ¹³C values were positively correlated with soil salinity and Na concentration, and negatively correlated with soil mineral nitrogen. The δ¹⁵N values of aboveground (6.7–16.1?‰, average: 9.6?±?0.4?‰) were comparatively higher than belowground biomass (5.4–13.2?‰, average: 7.8?±?0.3?‰). The δ¹⁵N values were negatively correlated with soil available P. We conclude that the variation in δ¹³C values of S. brachiata was possibly caused by soil salinity (associated Na content) and N limitation which demonstrates the potential of δ¹³C as an indicator of stress in plants.     

Temporal diet changes recorded by stable isotopes in Asiatic black bear (Ursus thibetanus) hair

Carbon and nitrogen stable isotope ratios were measured in hair samples of the Asiatic black bear (Ursus thibetanus) inhabiting the Northern Japanese Alps (NJA) (n?=?20) and the periphery of Nagano City (NC) (n?=?6), in Nagano Prefecture, Japan. The hair of NJA bears, which did not have access to anthropogenic foods, showed lower values of δ¹³C and δ¹⁵N than that of NC bears which had access to garbage and corn fields, especially during the summer. These results reflect somewhat differing diets between the NJA and NC bears. We attempted to assess the feeding history during the hair growth cycle using the growth section analysis method. Each hair sample had been cut into 3?mm lengths from root to tip, labeled, and analyzed along the hair growth. We measured the carbon and nitrogen stable isotope ratios of each 3?mm length of hair sample from one NC bear which had been killed while raiding a corn field. The sections showed wide ranges of isotope ratios, from ?23.2‰ to ?14.6‰ for δ¹³C, and from 0.3‰ to 4.6‰ for δ¹⁵N. It was shown that the diet of this bear shifted dramatically from principally C₃ plants to more C₄ plants and to foods of animal origin. An analysis of the whole hair reflects just the average feeding habit during hair growth, but the present method can trace its diet history. This method can contribute to obtain precise ecological information of wildlife.     

13C and 15N Abundances in the Sediment Core (VER 92/1-St-10-GC2) from Northern Lake Baikal

Abstract

Carbon and nitrogen stable isotope compositions of organic matter, TOC/TN ratio, and manganese concentration in a sediment core that was collected in northern part of Lake Baikal (VER92ST10-GC2, water depth at 922 m, about 3 m long) were investigated to elucidate the origin of the sedimentary organic matter and its associated environmental factors.

The sediment core was composed of mainly two parts: turbidite sections and other sections. Constant δ¹³C and δ¹⁵N values of the turbidite sections were observed (- 26.8 ±0.2 ‰ for δ¹³C and 3.2 ± 0.1 ‰ for δ¹⁵N) throughout the core. The higher δ¹³C in turbidite sections (about - 27 ‰) than that of the other sections (- 31 to - 29 ‰) was clearly observed, and δ¹⁵N was different between turbidite sections (about 3‰) and other sections (3 to 5 ‰). δ¹³C of other sections was close to that of pelagic phytoplankton, indicating that sediment other than turbidite sections is composed of autochthonous components. The variation of stable isotopes in other sections may be possibly caused by the changes in either phytoplankton growth rate or contribution ratios of terrestrial to aquatic plants for δ¹³C. Either denitrification or fluctuation of δ¹⁵N in pelagic phytoplankton can be the cause of variable δ¹⁵N in other sections.     

Tracing the pathways of Neotropical migratory shorebirds using stable isotopes: A pilot study

We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper (Calidris melanotos), the White-rumped Sandpiper (Calidris fuscicollis), the Baird's Sandpiper (Calidris bairdii), and other Neotropical migratory shorebird species (e.g., Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and (2) analyzing the deuterium and ¹⁸O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (δ¹³C, δ¹⁵N and δ³⁴S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, δ³⁴S was most important, followed by δ¹⁵N, and then δ¹³C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis δ¹³C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both δD and δ¹⁸O were significantly related to both latitude and longitude on a countrywide scale (p < 0.001). Other variables, month, altitude, explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the δD and δ¹⁸O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local δD and δ¹⁸O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues.     

Unusual patterns in 15N blood values after a diet switch in red knot shorebirds

When a diet switch results in a change in dietary isotopic values, isotope ratios of the consumer's tissues will change until a new equilibrium is reached. This change is generally best described by an exponential decay curve. Indeed, after a diet switch in captive red knot shorebirds (Calidris canutus islandica), the depletion of ¹³C in both blood cells and plasma followed an exponential decay curve. Surprisingly, the diet switch with a dietary ¹⁵N/¹⁴N ratio (δ¹⁵N) change from 11.4 to 8.8 ‰ had little effect on δ¹⁵N in the same tissues. The diet-plasma and diet-cellular discrimination factors of ¹⁵N with the initial diet were very low (0.5 and 0.2 ‰, respectively). δ¹⁵N in blood cells and plasma decreased linearly with increasing body mass, explaining about 40 % of the variation in δ¹⁵N. δ¹⁵N in plasma also decreased with increasing body-mass change (r ²=.07). This suggests that the unusual variation in δ¹⁵N with time after the diet switch was due to interferences with simultaneous changes in body-protein turnover.     

Wild Rabbit Host and Some Parasites Show Trophic-Level Relationships for δ13C and δ15N: A First Report

Abstract

We report the first isotopic study of an animal host-parasite system. Parasitic, intestinal nematodes, Graphidium strigosum and Passalurus ambiguus, were ¹⁵N-enriched relative to their host, the European rabbit Oryctolagus cuniculus, while parasitic cestodes, Cittataenia denticulata and Mosgovoyia pectinata, were ¹⁵N-depleted, suggesting different trophic relationships. Host embryos were more similar in their δ¹³C and δ¹⁵N values to maternal muscle than were any of the parasites. Coprophagy, the direct recycling of food by the rabbit eating its own faeces, did not lead to isotopic differences between stomach contents and faeces, suggesting that the major point for isotopic discrimination in lagomorph nitrogen metabolism is in the animal rather than in the gut. We conclude that bulk δ¹³C and δ¹⁵N can reveal valuable new information about host-parasite relationships, and these could be explored further at the biochemical level using compound-specific isotopic analyses.     

Long term changes in the distribution and δ15N values of individual soil amino acids in the absence of plant and fertiliser inputs

The long-term ‘biodegradation’ on soil amino acids was examined in the control plots of ‘42 parcelles’ experiment, established in 1928 at INRA, Versailles (France). None of the plots is cultivated, but is kept free of weeds, and mixed to a depth of 25 cm twice yearly. Topsoil (0–10 cm depth) samples collected in 1929, 1963 and 1997 were subjected to acid hydrolysis (6 N HCl) for comparison. The distribution and δ¹⁵N natural abundance of 20 individual amino acids in the soils were determined, using ion chromatography (IC) and gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS). The total N and amino acid-N (AA-N), respectively, decreased by 54 % and 73 % in the period from 1929 to 1997. The average N loss was comparable for 1929–1963 (period 1) and 1963–1997 (period 2), but AA-N loss was three times faster in the former period. This significant reduction in total AA-N content was mirrored in the individual amino acids, which decreased by 74 %?±?1 % (ranging 58–89 %) between 1929 and 1997. The bulk δ¹⁵N values generally increased from 1929 to 1997, mainly associated with comparable or even higher increase of δ¹⁵N of the non-AA-N in the soil. The residence time (t _1/2, time in which half of N was lost from a specific soil pool) was ca. 65?±?5 years for the bulk soil, and comparable for periods 1 and 2. However, between periods 1 and 2 it decreased from 128 to 41 years in the non-AA pool, but increased from 59 to 92 years in the AA-N pool. Proline and amino acids that appear early in soil microbial metabolic pathways (e.g. glutamic acid, alanine, aspartic acid and valine) had relatively high δ¹⁵N values. Phenylalanine, threonine, glycine and leucine had relatively depleted δ¹⁵N values. The average δ¹⁵N value of the individual amino acids (IAAs) increased by 1δ unit from 1929 to 1997, associated with a similar rise from 1929 to 1963, and no change thereafter till 1997. However, the δ¹⁵N values of phenylalanine decreased by more than 7δ¹⁵N units between 1929 and 1997. The δ¹⁵N shift of IAAs from 1929 to 1963 and from 1929 to 1997 was not influenced by the relative amount of N remaining compared with the 1929 soil concentrations. The only exception was phenylalanine which showed decreasing δ¹⁵N associated with its decreasing concentration in the soil. We conclude therefore that in the absence of plant and fertiliser inputs, no change in the δ¹⁵N value of individual soil amino acids occurs, hence the original δ¹⁵N values are preserved and diagnostic information on past soil N (cycling) is retained. The exception was phenylalanine, its δ¹⁵N decreased with decreasing concentration from 1929 to 1997, hence it acted as a ‘potential’ marker for the land use changes (i.e. arable cropping to a fallow). The long term biological processing and reworking of residual amino acids resulted in a (partial) stabilisation in the soil, evidenced by reduced N loss and increased residence time of amino acid N during the period 1963–1997.     

Estimating Spatial and Seasonal Phytoplankton δ13C Variations in an Estuarine Mangrove Ecosystem

Abstract

In estuarine ecosystems, large spatial and seasonal variations in δ¹³C values of primary producers can occur, and knowledge of these variations may be crucial when interpreting stable isotope data of higher trophic levels. Obtaining clean phytoplankton samples for isotope analysis is usually impossible in such systems, and analysis of total suspended matter is not a simple proxy for phytoplankton δ¹³C variations. Based on a few simple assumptions regarding the C and N content of the two end-members (terrestrial detritus and phytoplankton) and the δ¹³C of the terrestrial component, we here present a simple model to estimate the phytoplankton δ¹³C variations using an existing dataset on the δ¹³C and elemental (C:N) composition of suspended organic matter from an estuarine mangrove ecosystem in southeast India.

These variations are related to the monthly rainfall pattern during the sampling period. It is stressed that this method estimates approximate phytoplankton δ¹³C values, which should not be used in e.g., mixing models. However, we propose that in cases where sufficiently large datasets are available, the described procedure could provide a valuable method to semi-quantitatively estimate the seasonal or spatial variations of the phytoplankton δ¹³C signal.     

Factors Influencing Stable Isotope Ratios in CH4 and CO2 Within Subenvironments of Freshwater Wetlands: Implications for δ-Signatures of Emissions

Abstract

Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios (¹³C/¹²C and D/H) in different CH₄-emission sources. Such variability is especially prevalent in freshwater wetlands where a range of processes can influence stable isotope compositions, resulting in variations of up to ～50‰ for δ¹³C-CH₄ and ～150‰ for δD-CH₄ values. Within a temperate-zone bog and marsh situated in southwestern Ontario, Canada, gas bubbles in pond sediments exhibit only minor seasonal and spatial variation in δ¹³C-CH₄, δD-CH₄ and δ¹³C-CO₂ values. In pond sediments, CO₂ appears to be the main source of carbon during methanogenesis either directly via CO₂ reduction or indirectly through dissimilation of autotrophic acetate. In contrast, CH₄ production occurs primarily via acetate fermentation at shallow depths in peat soils adjacent to ponds at each wetland. At greater depths within soils, σCO₂ and H₂O increasingly exert an influence on δ¹³C- and δD-CH₄ values. Secondary alteration processes (e.g., methanotrophy or diffusive transport) are unlikely to be responsible for depth-related changes in stable isotope values of CH₄. Recent models that attempt to predict δD-CH₄ values in freshwater environments from D/H ratios in local precipitation do not adequately account for such changes with depth. Subenvironments (i.e., soil-forming and open water areas) in wetlands should be considered separately with respect to stable isotope signatures in CH₄ emission models.     

Estimates of dietary overlap for six species of Amazonian manakin birds using stable isotopes

We used stable isotope ratios to determine the metabolic routing fraction of carbon and nitrogen in feathers in addition to faecal analysis to estimate diet overlap of six sympatric species of manakins in the eastern lowland forest of Ecuador. Collectively, all species varied from?23.7 to?32.7 ‰ for δ¹³C, and from 6.0 to 9.9‰ for δ¹⁵N, with Machaeropterus regulus showing isotopic differences from the other species. We developed a mixing model that explicitly addresses the routing of carbon and nitrogen to feathers. Interestingly, these results suggest a higher proportion of nitrogen and carbon derived from insects than anticipated based on feeding observations and faecal analysis. A concentration-dependent mixing isotopic model was also used to look at dietary proportions. While larvae and arachnids had higher δ¹⁵N values, these two groups may also be preferred prey of manakins and may be more assimilated into tissues, leading to a potential overestimation of the contribution to diet. This study supports the finding that manakin species, previously thought be primarily frugivorous, contain a significant amount of arthropods in their diet.     

Nitrogen isotope pattern in Mongolian larch stands at the southern Eurasian boreal forest boundary

ABSTRACT

In the last decades a drastic increase in air temperature but a stable precipitation regime in Mongolia has led to gradual drying conditions. Thus, we evaluated the effect of spatial and climatic characteristics on the soil–plant nitrogen dynamics in three representative larch stands (Larix sibirica) with different geographical and climatic conditions using stable nitrogen isotopes. The results showed significant differences in the soil inorganic N content among sites and consequently a different isotopic composition in the plant–soil system. Litter, bark and wood had the lowest δ¹⁵N values for all sites, slightly higher δ¹⁵N values for needles, while the highest δ¹⁵N values were observed for roots and soil. These differences could be the result of the larch stands age themselves, but were in agreement with the spatial and climatic characteristics of the sites. Based on the δ¹⁵N value a higher reliance on ectomycorrhizal fungi (ECMF) was observed in the warmest and driest site, while lower dependency was shown in the cooler northern site with higher soil inorganic N content. In both sites, the rate of air temperature increase has been similar in the last decades; however, their soil–plant N dynamics showed different characteristics.     

Source attribution of agriculture-related deposition by using total nitrogen and δ15N in epiphytic lichen tissue,bark and deposition water samples in Germany

Compared with physico-chemical deposition measurement methods, lichens are able to identify the long-term overall effects of high N pollution concentrations in the air. In addition, the natural abundances of the stable isotope of N, ¹⁵N, are being widely used in research on N cycling in ecosystems. They can also be used as instruments for source attribution. In this study, epiphytic lichens were tested to determine whether their respective N content and δ¹⁵N ratios can be used to estimate N deposition rates and to locate various sources of N compounds. Epiphytic lichen and bark samples were collected from around various deposition measurement field stations at different sites in the western part of Germany. The N content of epiphytic lichens reflects the species-specific, agriculture-related circumstances of N deposition at various sites in Germany. At the same time, δ¹⁵N signatures of the different investigated epiphytic lichen species and bark samples are highly depleted in ¹⁵N under high ammonium deposition. The different surface types of lichens and barks exhibit different concentrations of N and δ¹⁵N ratios, despite being exposed to similar N deposition rates. The verification of highly negative δ¹⁵N ratios at sites with local and regional emitters shows that source attribution is possible by comparing different δ¹⁵N signatures in areas with a wide range of different N deposition types and the corresponding differences in δ¹⁵N among various source N pools. Especially nitrophytic lichens can support the on-site instrumentation measuring N deposition by qualification and quantification.     

Food webs in Mongolian grasslands: The analysis of 13C and 15N natural abundances

Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the δ¹³C and δ¹⁵N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central Mongolia to understand the predominant food-web pathways in this grassland ecosystem. The δ¹³C and δ¹⁵N values of mammals showed little variation within species, but varied considerably with slope position for arthropods. The apparent isotopic discrimination between body tissue and hair of mammals was estimated as 2.0 ‰ for δ¹³C and 2.1 ‰ for δ¹⁵N, which was large enough to cause overestimation of the trophic level of mammals if not taken into account when using hair samples to measure isotopic enrichment.     

Natural abundances of 15N and 13C in leaves of some N2-fixing and non-N2-fixing trees and shrubs in Syria

A survey study was conducted on man-made plantations located at two different areas in the arid region of Syria to determine the variations in natural abundances of the ¹⁵N and ¹³C isotopes in leaves of several woody legume and non-legume species, and to better understand the consequence of such variations on nitrogen fixation and carbon assimilation. In the first study area (non-saline soil), the δ¹⁵N values in four legume species (Acacia cyanophylla,?1.73 ‰ Acacia farnesiana,?0.55 ‰ Prosopis juliflora,?1.64 ‰; and Medicago arborea,+1.6 \textperthousand) and one actinorhizal plant (Elaeagnus angustifolia,?0.46 to?2.1 ‰) were found to be close to that of the atmospheric value pointing to a major contribution of N₂ fixing in these species; whereas, δ¹⁵N values of the non-fixing plant species were highly positive. δ¹³C ‰; in leaves of the C3 plants were found to be affected by plant species, ranging from a minimum of?28.67 ‰; to a maximum of?23 ‰. However, they were relatively similar within each plant species although they were grown at different sites. In the second study area (salt affected soil), a higher carbon discrimination value (Δ¹³C ‰) was exhibited by P. juliflora, indicating that the latter is a salt tolerant species; however, its δ¹⁵N was highly positive (+7.03 ‰) suggesting a negligible contribution of the fixed N₂. Hence, it was concluded that the enhancement of N₂ fixation might be achieved by selection of salt-tolerant Rhizobium strains.