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1.
Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ 13C) in photosynthetic tissues of C3 plants is an indicator of time‐integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ 15N) is an indicator of the main source of plant N (soil N vs. atmospheric N 2). Previous studies in drylands have documented that plant δ 13C and δ 15N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in 15N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ 13C, δ 15N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central‐western Argentinian drylands. Noticeably, plant δ 13C and δ 15N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ 13C and δ 15N. The short‐term environmental conditions may interact with species‐specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ 13C and δ 15N widely reported in drylands. 相似文献
2.
Nitrogen availability and N‐cycling dynamics across ecosystems play a critical role in plant functioning and species distribution. Measurements of 15N natural abundance provides a way to assess ecosystem N dynamics, and the range of nitrogen stable isotope values (δ 15N) for plants in an ecosystem can indicate divergent strategies for N uptake. We tested the hypotheses that the N‐rich seasonally dry forest would have higher soil and leaf δ 15N and a smaller range of leaf δ 15N values compared to the N‐poor cerradão (savanna woodland). We measured N concentration and δ 15N in two soil depths and leaves of 27 woody species in cerradão and 26 in seasonally dry forest. As expected, total soil N concentration decreased while soil δ 15N value increased with soil depth. Regardless of soil depth, seasonally dry forest soils had higher δ 15N and total N concentration compared to cerradão soils. Foliar δ 15N values varied from ?6.4‰ to 5.9‰ in cerradão and from ?2.3‰ to 8.4‰ in seasonally dry forest plants. Phylogenetically independent contrasts analysis and comparisons of δ 15N mean values of the most abundant species and species co‐occurring in both sites confirmed the hypothesis of higher δ 15N for seasonally dry forest in comparison to cerradão. These results corroborate the expectation of higher soil and leaf δ 15N values in sites with higher soil N availability. However, except for the most abundant species, no across‐site leaf–soil (δ 15N leaf –δ 15N soil) differences (Δδ 15N) were found suggesting that differences in leaf δ 15N between cerradão and seasonally dry forest are driven by differences in soil δ 15N. Variation of leaf δ 15N was large in both sites and only slightly higher in cerradão, suggesting high diversity of N use strategies for both cerradão and seasonally dry forest communities. 相似文献
3.
Stable nitrogen (δ 15N) and carbon (δ 13C) isotope ratios from muscle, liver and yolk were analysed from the mother and embryos of an ovoviviparous shark, Hexanchus griseus. Embryonic liver and muscle had similar δ 15N and δ 13C ratios or were depleted in heavy isotopes, compared to the same maternal somatic and reproductive yolk tissues, but no relationship existed between δ 15N or δ 13C and embryo length, as expected, because a switch to placental nourishment is lacking in this species. This study expands the understanding of maternal nourishment and embryonic stable isotope differences in ovoviviparous sharks. 相似文献
4.
The ratios of stable nitrogen isotopes expressed as δ 15N values can indicate the openness of nitrogen cycles in ecosystems. Southwards through the Northern Territory, values of foliar δ 15N in savanna trees increase as mean annual rainfall decreases from approximately 1800 mm to approximately 750 mm, with foliar δ 15N thereafter decreasing toward arid central Australia. Recent literature argues that this pattern is caused by higher grazing intensity in semi‐arid savannas, but counter views have attributed the pattern more directly to variations in aridity. In this paper, grazed and ungrazed sites in a semi‐arid savanna are compared, and it is shown that grazing has a relatively small effect on the positive foliar δ 15N values of grasses, but no effect on δ 15N values of trees. This gives little support to the argument that variations in grazing pressure at the scale of hundreds of kilometres could result in detectable differences in the foliar δ 15N values of trees. I then compare the semi‐arid savannas with mesic savannas, where fires are frequent, and with mesic rainforests, which are rarely burnt. Greater foliar δ 15N values in rainforest and fire‐excluded mesic savannas than in frequently burnt savannas suggests that fire regimes affect foliar δ 15N. The previously observed pattern in δ 15N values along the rainfall gradient in the Northern Territory is consistent with trends in fire frequency and possible direct effects of fire, but further work is required to determine the relative impacts of aridity and fire. Within a particular rainfall regime, foliar δ 15N values may indicate historical fire frequencies. 相似文献
5.
Background and aims The aim of this study is to enhance our knowledge of nitrogen (N) cycling and N acquisition in tropical montane forests through analysis of stable N isotopes (δ 15N). Methods Leaves from eight common tree species, leaf litter, soils from three depths and roots were sampled from two contrasting montane forest types in Jamaica (mull ridge and mor ridge) and were analysed for δ 15N. Results All foliar δ 15N values were negative and varied among the tree species but were significantly more negative in the mor ridge forest (by about 2 ‰). δ 15N of soils and roots were also more negative in mor ridge forests by about 3 ‰. Foliar δ 15N values were closer to that of soil ammonium than soil nitrate suggesting that trees in these forests may have a preference for ammonium; this may explain the high losses of nitrate from similar tropical montane forests. There was no correlation between the rankings of foliar δ 15N in the two forest types suggesting a changing uptake ratio of different N forms between forest types. Conclusions These results indicate that N is found at low concentrations in this ecosystem and that there is a tighter N cycle in the mor ridge forest, confirmed by reduced nitrogen availability and lower rates of nitrification. Overall, soil or root δ 15N values are more useful in assessing ecosystem N cycling patterns as different tree species showed differences in foliar δ 15N between the two forest types. 相似文献
6.
The foliar natural abundance of 15N was analysed to compare the potential nitrogen sources of vascular rainforest epiphytes and associated soil-rooted trees. Leaves of epiphytes collected from six rainforest communities in Brazil, Australia and the Solomon Islands were depleted in 15N relative to the trees at each site. Epiphyte δ 15N was as low as -6.4% o, while trees were generally enriched in 15N (0.7 to 3.5% o). These results indicate either that epiphytes use nitrogen sources depleted in 15N or that discrimination against 15N is an intrinsic function of epiphyte physiology. At three sites, epiphytes could be grouped into those having both low δ 15N and low leaf-nitrogen content and those possessing both high δ 15N and high leaf-nitrogen content. The second group had δ 15N values in the range sometimes attributable to N 2 fixation (-2 to 0%o). There was no correlation between growth form and δ 15N. It is concluded that epiphytes may utilize 15N-depleted nitrogen from atmospheric deposition and N 2 fixation. 相似文献
7.
The nitrogen isotope ratio (δ 15N) in tissues of native macroalgae was evaluated as a means of indicating the intensity and spatial extent of organic contamination due to disposal of waste from land-based marine fish farms (LBMFFs). Three species of macroalgae from the genus Fucus and the green macroalgae Codium tomentosum were selected for study. The study was carried out at seven flat marine fish farms located in Galicia (NW Spain). Tests were carried out to determine the intra-annual variation in δ 15N values and any differences between selected macroalgae. The δ 15N values enrichment was observed close to the disposal point, and δ 15N values varied more widely throughout the year (±5.57 ‰) at sites affected by the marine fish farm effluent compared to natural conditions (±2 ‰). No significant differences in the isotopic signals were observed in the different species studied (standard major axis). The δ 15N values of macroalgae may be an ideal means of detecting the presence of LBMFFs effluents. 相似文献
8.
Studies of the variation in δ 15N values for plants from a fire-prone Banksia woodland in South West Australia showed that pioneer herbaceous, non-mycorrhizal species which were active in nitrate reduction and storage, had the highest values (1.81%c). A detailed study of one such species Ptilotus polystachus demonstrated a close correspondence between the δ 15N values of soil nitrate, xylem nitrate and leaf total nitrogen, suggesting an exclusive reliance on nitrate ions as nitrogen source. These pioneer species also showed a preponderance of the chloroplastic isoform of glutamine synthetase while woody species generally had higher activity associated with the cytosolic isoform. The group comprising monocotyledonous hemicryptophytes and geophytes contained species with slightly positive δ 15N values and moderately active in nitrate reduction and storage. Nitrogen-fixing species had the lowest δ 15N values (–0.36‰), irrespective of their apparent utilisation of nitrate. However, woody resprouter species which had low levels of nitrate reduction and storage had δ 15N values which fell within the range of values obtained for the miscellaneous assemblage of N 2-fixing species. Consequently, 15N abundance values failed to distinguish N 2 fixing from non-fixing woody species, and therefore, could not be used in the ecosystem to determine the dependence of putative nitrogen fixing species on N 2 fixation. The study demonstrated complex patterns of nitrogen utilization in the ecosystem in which exploitation of different nitrogen resources related to plant life form and the physiological attributes of nitrogen assimilation by component species. 相似文献
9.
Green sturgeon ( Acipenser medirostris) and white sturgeon ( A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ 13C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ 15N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ 15N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ 13C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ 15N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay. 相似文献
10.
A 210Pb-dated sediment core from a small bay in the southern basin of Lake Petén Itzá, Guatemala documents recent cultural eutrophication. Increased sediment accumulation beginning ~1930 A.D. coincided with catchment population growth and was a consequence of watershed deforestation and increased surface run-off. At the same time, geochemical records from the Lake Petén Itzá sediment core indicate increased phosphorus loading and organic matter accumulation. High nutrient concentrations after 1965 A.D. coincided with lower sediment C/N ratios, suggesting an increase in the relative contribution of phytoplankton to the organic matter pool. This inference is confirmed by the dominance of eutrophic and hypereutrophic diatom species. Organic matter δ 13C values decreased after 1965 A.D., seemingly contradicting other indicators of recent eutrophication in the southern basin of Lake Petén Itzá. Relatively depleted δ 13C values in recent sediments, however, may reflect a contribution from 13C-depleted sewage effluent. Increased δ 15N of organic matter after 1965 A.D. indicates changes in the dissolved inorganic nitrogen delivered to the lake. The relatively small increase in δ 15N (~0.6‰ ) is less than might be expected with nitrate loading from sewage and soils, and might be offset by the presence of nitrogen-fixing cyanobacteria with low δ 15N values. 相似文献
11.
Nitrogen stable isotope analysis studies have become a useful tool in dietary studies to quantify differences in diet composition among species or individuals. However, laboratory studies have revealed several factors that influence the nitrogen isotope ratios (δ 15N) in animal tissues (e.g. habitat, amount of ingested food, and metabolic rate). The influence of these factors has not been validated for free-ranging bat species, which is important for interpreting nitrogen isotope data in field studies. In this study, we measured δ 15N from wing membranes (δ 15N w) and habitat samples (δ 15N h; soil and leaf, or sediment) to test for effects of diet, age, and individual energy demand in three free-living bat species ( Myotis daubentonii, Nyctalus noctula and Nyctalus leisleri). We hypothesised that based on differences in diet composition δ 15N w values should increase in the sequence M. daubentonii, N. leisleri, and highest N. noctula. Furthermore, juveniles should have significantly lower δ 15N w compared to their mothers. Thirdly, the δ 15N w values of reproductively active individuals should be significantly higher than those of non-reproductive individuals. Values of δ 15N w were significantly influenced by differences in feeding ecology among species and individual reproductive status, but not by animal age. Our results show that species feeding on primary consumers have lower δ 15N w values than species feeding on secondary and tertiary consumers. Further, independent young did not differ in their δ 15N w values from adults suggesting that their tissues already reflect the insect diet. The effect of reproductive status varied among species which might reflect intra-specific differences in foraging behaviour of generalist vs. specialist species. In this study, we demonstrated that δ 15N can provide information on the dietary range of bats, but researchers should account for variation owing to reproductive status, habitat, and species. 相似文献
12.
Stable nitrogen (δ 15N) and carbon (δ 13C) isotopes of Atlantic sharpnose shark Rhizoprionodon terraenovae embryos and mothers were analysed. Embryos were generally enriched in 15N in all studied tissue relative to their mothers' tissue, with mean differences between mother and embryo δ 15N (i.e. Δδ 15N) being 1·4‰ for muscle, 1·7‰ for liver and 1·1‰ for cartilage. Embryo muscle and liver were enriched in 13C (both Δδ 13C means = 1·5‰) and embryo cartilage was depleted (Δδ 13C mean = ?1·01‰) relative to corresponding maternal tissues. While differences in δ 15N and δ 13C between mothers and their embryos were significant, muscle δ 15N values indicated embryos to be within the range of values expected if they occupied a similar trophic position as their respective mothers. Positive linear relationships existed between embryo total length ( LT) and Δδ 15N for muscle and liver and embryo LT and Δδ 13C for muscle, with those associations possibly resulting from physiological differences between smaller and larger embryos or differences associated with the known embryonic nutrition shift (yolk feeding to placental feeding) that occurs during the gestation of this placentatrophic species. Together these results suggest that at birth, the δ 15N and δ 13C values of R. terraenovae are likely higher than somewhat older neonates whose postpartum feeding habits have restructured their isotope profiles to reflect their postembryonic diet. 相似文献
13.
Wood nitrogen isotope composition (δ 15N) provides a potential retrospective evaluation of ecosystem N status but refinement of this index is needed. We calibrated current wood δ 15N of Douglas-fir ( Pseudotsuga menziesii), an ectomycorrhizal tree species, against a productivity gradient of contrasting coastal forests of southern Vancouver Island (Canada). We then examined historical δ 15N via increment cores, and tested whether wood δ 15N corresponded with climatic fluctuations. Extractable soil N ranged from 11 to 43 kg N ha ?1 along the productivity gradient, and was characterized by a progressive replacement of N forms (amino acids, NH 4 + and NO 3 ?). Current wood δ 15N was significantly less depleted (?5.0 to ?2.6 ‰) with increasing productivity, although linear correlations were stronger with Δδ 15N (the difference between wood and soil δ 15N) to standardize the extent of isotopic fractionation by ectomycorrhizal fungi. An overall decline in wood δ 15N of 0.9 ‰ over the years 1900–2009 was detected, but trends diverged widely among plots, including positive, negative and no trend with time. We did not detect significant correlations in detrended wood δ 15N with mean annual temperature or precipitation. The contemporary patterns in stand productivity, soil N supply and wood δ 15N were moderately strong, but interpreting historical patterns in δ 15N was challenging because of potential variations in N uptake related to stand dynamics. The lack of wood δ 15N correlations with climate may be partly due to methodological limitations, but might also reflect the relative stability in N supply due to the overriding constraints of soil organic matter quantity and quality. 相似文献
14.
Key message Large variations in leaf δ 15 N in Bornean tropical rainforest trees may indicate that various tropical species have species-specific strategy for nitrogen uptake under low soil nutrient conditions, including root symbiotic microorganisms such as ectomycorrhiza. AbstractLowland tropical rainforests in Southeast Asia are characterized by high species diversity despite limited soil nutrient conditions. The plant nitrogen isotope ratio (δ15N) reflects plant uptake of soil nitrogen. We analyzed δ15N values and nitrogen content (N %) in leaves and roots of 108 woody species with different types of symbiotic microorganisms, of different life forms (emergent, canopy, sub-canopy, understory, and canopy gap species), and from different families in a Bornean lowland dipterocarp forest to gain more insight into the diversity of nitrogen uptake strategy in the rhizosphere. Leaf δ15N values in the species studied varied largely from ?7.2 to 5.0 ‰, which is comparable to the values of known Asian trees including temperate, sub-tropical, and tropical mountain forests. Leaf δ15N also varied significantly among both life forms and families, though the phylogenetically independent contrast (PIC) relationships were not statistically significant among life form, family, and symbiotic types. Some families showed specific leaf δ15N values; Dipterocarpaceae, the dominant family in the canopy layer with symbiotic ectomycorrhiza in Southeast Asia, had small intraspecific variation and higher leaf δ15N values (0.03 ‰) compared with species exhibiting arbuscular mycorrhiza, whereas several families such as Burseraceae, Euphorbiaceae, and Myrtaceae showed large interspecific variation in leaf δ15N (e.g., from ?7.2 to 5.0 ‰ in Euphorbiaceae). These variations suggest that tropical species may have family- or species-specific strategy, such as root symbiotic microorganisms, for nitrogen uptake under low-nutrient conditions in tropical rainforests in Southeast Asia. 相似文献
15.
The foliar stable N isotope ratio (δ 15N) can provide integrated information on ecosystem N cycling. Here we present the δ 15N of plant and soil in four remote typical tropical rainforests (one primary and three secondary) of southern China. We aimed to examine if (1) foliar δ 15N in the study forests is negative, as observed in other tropical and subtropical sites in eastern Asia; (2) variation in δ 15N among different species is smaller compared to that in many N-limited temperate and boreal ecosystems; and (3) the primary forest is more N rich than the younger secondary forests and therefore is more 15N enriched. Our results show that foliar δ 15N ranged from ?5.1 to 1.3 ‰ for 39 collected plant species with different growth strategies and mycorrhizal types, and that for 35 species it was negative. Soil NO 3 ? had low δ 15N (?11.4 to ?3.2 ‰) and plant NO 3 ? uptake could not explain the negative foliar δ 15N values (NH 4 + was dominant in the soil inorganic-N fraction). We suggest that negative values might be caused by isotope fractionation during soil NH 4 + uptake and mycorrhizal N transfer, and by direct uptake of atmospheric NH 3/NH 4 +. The variation in foliar δ 15N among species (by about 6 ‰) was smaller than in many N-limited ecosystems, which is typically about or over 10 ‰. The primary forest had a larger N capital in plants than the secondary forests. Foliar δ 15N and the enrichment factor (foliar δ 15N minus soil δ 15N) were higher in the primary forest than in the secondary forests, albeit differences were small, while there was no consistent pattern in soil δ 15N between primary and secondary forests. 相似文献
16.
Protein, amino acids and ammonium were the main forms of soluble soil nitrogen in the soil solution of a subtropical heathland (wallum). After fire, soil ammonium and nitrate increased 90- and 60-fold, respectively. Despite this increase in nitrate availability after fire, wallum species exhibited uniformly low nitrate reductase activities and low leaf and xylem nitrate. During waterlogging soil amino acids increased, particularly γ-aminobutyric acid (GABA) which accounted for over 50% of amino nitrogen. Non-mycorrhizal wallum species were significantly ( P < 0.05) 15N-enriched (0.3–4.3‰) compared to species with mycorrhizal associations (ericoid-type, ecto-, va-mycorrhizal) which were strongly depleted in 15N (-6.3 to -1.8‰). Lignotubers and roots had δ 15N signatures similar to that of the leaves of respective species. The exceptions were fine roots of ecto-, ecto/va-, and ericoid type mycorrhizal species which were enriched in 15N (0.1–2.4‰). The 5 15N signatures of δ 15N total soil N and δ 15N soil NH4+ were in the range 3.7–4.5‰, whereas δ 15N soil NO3? was significantly ( P < 0.05) more enriched in 15N (9.2–9.8‰). It is proposed that there is discrimination against 15N during transfer of nitrogen from fungal to plant partner. Roots of selected species incorporated nitrogen sources in the order of preference: ammonium > glycine > nitrate. The exception were proteoid roots of Hakea (Proteaceae) which incorporated equal amounts of glycine and ammonium. 相似文献
17.
Stable isotopes are increasingly being used to infer past and present trophic interactions in light of environmental changes. The Lake Victoria haplochromine cichlids have experienced severe environmental changes in the past decades that, amongst others, resulted in a dietary shift towards larger prey. We investigated how the changed environment and diet of the haplochromines influenced stable isotope values of formalin-then-ethanol-preserved cichlid specimens, and then investigated how these values differed among species before (1977–1982) and after substantial environmental changes (2005–2007). We found a small preservation effect on both δ 13C and δ 15N values, and significant differences in isotope values among haplochromine species collected before the environmental changes. In contrast, there was a remarkable similarity in δ 13C and δ 15N values among species collected from the contemporary ecosystem and two out three species showed significantly different stable isotope values compared to species of the historic ecosystem. In addition, we found a putative isotopic gradient effect along our 5-km-long research transect indicating that the studied demersal species are more stenotopic than previously thought. The environmental changes have resulted in dietary change and overlap of the haplochromines which provides insight into the trophic plasticity of these species, which are often considered trophic specialists. 相似文献
18.
BackgroundAnthropogenic nitrogen (N) addition has dramatically increased and significantly affected global nitrogen cycling. The natural abundance of stable N isotope ratios (δ15N) has been used as an indicator of the N status of an ecosystem. However, how plant and soil δ15N signatures would respond to N addition is still unclear. Methods and aimsHerein, we synthesized the data of 951 observations from 48 individual studies associated with responses of plant and soil δ15N values to N addition and conducted a meta-analysis to explore a general pattern of N addition effects on δ15N values of plant and soil. ResultsOur results showed that δ15N values of plant, soil total N, and soil NO3
? were significantly increased by N addition, while δ15N value of soil N2O was significantly decreased and δ15N value of soil NH4
+ was not significantly changed. The δ15N value of soil total N of different ecosystems showed similar responses to N addition, whereas δ15N values of different plant types showed different responses. Increasing treatment duration significantly increased the effects of inorganic N addition on δ15N values of shrubs and soil NH4
+ but did not affect the responses of δ15N values of soil total N and NO3
?. With increasing inorganic N addition rate, only δ15N value of plant was significantly increased, but no significant relationship was found between the effect of N addition on other components and N addition rate because of the input of isotopically depleted sources. ConclusionsOur study revealed a comprehensive picture of the effects of N addition on δ15N signatures in terrestrial ecosystems and could help us understand how plant and soil δ15N signatures change with N addition and how these signatures can be used as an indicator of ecosystem N status under increasing N deposition or fertilization. 相似文献
19.
The present study explores the xylem‐tapping parasitism by mistletoe ( Tapinanthus oleifolius) on native tree species along the Kalahari Transect (KT) using the stable isotopes of carbon and nitrogen. Mistletoe‐host pairs were collected at three geographical locations along the KT rainfall gradient in the 2005 and 2006 wet seasons. Foliar total carbon, total nitrogen and their stable isotope compositions (δ 13C and δ 15N) were measured. Heterotrophy ( H) was calculated using foliar δ 13C values of mistletoes and their hosts as an indicator of proportion of carbon in the mistletoes derived from host photosynthate. Based on the mistletoe H‐value and relationship between the mistletoe foliar δ 15N and their host foliar δ 15N, the results showed that mistletoes along the KT derived both nitrogen and carbon from their hosts. Mistletoes may regulate water use in relation to nitrogen supply. The proportion of carbon in the mistletoes derived from host photosynthate was between 35% and 78%, and the degree of heterotrophy was species‐specific with only limited annual variation. The study emphasizes the importance of incorporating parasitic associations in future studies on studying carbon, water and nutrient cycling along the Kalahari. 相似文献
20.
Differences in trophic niches among carabid beetles (Coleoptera: Carabidae) co‐occurring on the forest floors of warm temperate forests in central Japan were studied using carbon (δ 13C) and nitrogen (δ 15N) stable isotope analyses. Different carabid species showed similar δ 15N values, which were higher than those of their possible invertebrate prey (herbivores and detritivores) collected from the litter layer, indicating that these species were consumers in the same trophic level. In contrast, δ 13C values differed among carabid species, indicating interspecific differences in prey animals. The variation in the δ 13C value was larger in summer than in autumn. In summer, δ 13C values indicated that some carabids depended highly on either grazing (low δ 13C values) or detrital sources (high δ 13C values) within the food chain [ Chlaenius posticalis Motschulsky and Haplochlaenius costiger (Chaudoir), respectively], although other species with intermediate δ 13C values likely depended on both. The latter group of species comprised mostly two dominant genera ( Carabus and Synuchus). Although congeners might have similar feeding habits, the stable isotope ratios indicated trophic niche differences between adults of different species and between adults and larvae of the same genus. 相似文献
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