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1.
Summary The mean stable-carbon isotope ratios (13C) for polar bear (Ursus maritimus) tissues (bone collagen –15.7, muscle –17.7, fat –24.7) were close to those of the same tissues from ringed seals (Phoca hispida) (–16.2, –18.1, and –26.1, respectively), which feed exclusively from the marine food chain. The 13C values for 4 species of fruits to which polar bears have access when on land in summer ranged from –27.8 to –26.2, typical of terrestrial plants in the Arctic. An animal's 13C signature reflects closely the 13C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.  相似文献   

2.
We analysed the stable isotope composition of emitted N2O in a one-year field experiment (June 1998 to April 1999) in unfertilized controls, and after adding nitrogen by applying slurry or mineral N (calcium ammonium nitrate). Emitted N2O was analysed every 2–4 weeks, with additional daily sampling for 10 days after each fertilizer application. In supplementary soil incubations, the isotopic composition of N2O was measured under defined conditions, favouring either denitrification or nitrification. Soil incubated for 48 h under conditions favouring nitrification emitted very little N2O (0.024 mol gdw –1) and still produced N2O from denitrification. Under denitrifying incubation conditions, much more N2O was formed (0.91 mol gdw –1 after 48 h). The isotope ratios of N2O emitted from denitrification stabilized at 15N = –40.8 ± 5.7 and 18O = 2.7 ± 6.3. In the field experiment, the N2O isotope data showed no clear seasonal trends or treatment effects. Annual means weighted by time and emission rate were 15N = –8.6 and 18O = 34.7 after slurry application, 15N = –4.6 and 18O = 24.0 after mineral fertilizer application and 15N = –6.4 and 18O = 35.6 in the control plots, respectively. So, in all treatments the emitted N2O was 15N-depleted compared to ambient air N2O (15N = 11.4 ± 11.6, 18O = 36.9 ± 10.7). Isotope analyses of the emitted N2O under field conditions per se allowed no unequivocal identification of the main N2O producing process. However, additional data on soil conditions and from laboratory experiments point to denitrification as the predominant N2O source. We concluded (1) that the isotope ratios of N2O emitted from the field soil were not only influenced by the source processes, but also by microbial reduction of N2O to N2 and (2) that N2O emission rates had to exceed 3.4 mol N2O m–2 h–1 to obtain reliable N2O isotope data.  相似文献   

3.
We examined the effects of fertilizer application, especially the effects of fertigation and types of fertilizer (inorganic and organic) on yields and 15N and 13C values of tomato (Lycopersicon esculentum Mill. cv. Saturn). Fertigation is a method in which an appropriate diluted liquid fertilizer is applied to the plants each time they are drip-irrigated. We developed a method of organic fertigation using corn steep liquor (CSL) as the liquid fertilizer, because it is an industrial byproduct of cornstarch manufacture and can be used very effectively. We compared fruit yield, mineral content, 15N value, and 13C value of tomatoes grown under three different fertilizer treatments, basal dressing: basal dressing with granular chemical fertilizer; inorganic fertigation: fertigation with liquid chemical fertilizer; and organic fertigation: fertigaion with CSL. Mineral contents of tomatoes grown with basal dressing were generally lower than those grown under either fertigation treatment. These results indicated that yields and mineral contents were influenced more by the method of fertilizer application than by whether the fertilizers were inorganic or organic. There were, however, significant differences in the 15N values of tomato fruits grown under different types of fertilizer applications, especially between inorganic and organic fertilizers. The 15N value of the chemical fertilizer used for basal dressing was 0.81 ± 0.45{}, that of the chemical fertilizer for fertigation was 0.00 ± 0.04{}, and that of CSL was 8.50 ± 0.71{}. The 15N values of the soils reflected the 15N values of the fertilizers. Moreover, the 15N values of the fruits corresponded to the 15N values of the applied fertilizers. The 15N values were 3.18 ± 1.34{} in the fruits grown with a basal dressing of chemical fertilizer, 0.30 ± 0.61 in those grown under inorganic fertigation, and 7.09 ± 0.68 in those grown under organic fertigation. On the other hand, although the 13C values in the soil also reflected the 13C values of the applied fertilizers, there was no significant difference in the 13C values of fruits among the different treatments. In conclusion, because the 15N values of fertilizers correlated well with those of the fruits, it may be possible to use 15N values as an indicator of organic products.  相似文献   

4.
The feasibility of using nitrogen and oxygenisotope ratios of nitrate (NO3 ) forelucidating sources and transformations ofriverine nitrate was evaluated in a comparativestudy of 16 watersheds in the northeastern U.S.A. Stream water was sampled repeatedly at theoutlets of the watersheds between January andDecember 1999 for determining concentrations,15N values, and 18Ovalues of riverine nitrate.In conjunction with information about land useand nitrogen fluxes,15Nnitrate and18Onitrate values providedmainly information about sources of riverinenitrate. In predominantly forested watersheds,riverine nitrate had mean concentrations ofless than 0.4 mg NO3 -N L–1,15Nnitrate values of lessthan +5, and 18Onitratevalues between +12 and +19. This indicatesthat riverine nitrate was almost exclusivelyderived from soil nitrification processes withpotentially minor nitrate contributions fromatmospheric deposition in some catchments. Inwatersheds with significant agricultural andurban land use, concentrations of riverinenitrate were as high as 2.6 mg NO3 -NL–1 with 15Nnitratevalues between +5 and +8 and18Onitrate values generallybelow +15. Correlations between nitrateconcentrations, 15Nnitratevalues, and N fluxes suggest that nitrate inwaste water constituted a major, and nitrate inmanure a minor additional source of riverinenitrate. Atmospheric nitrate deposition ornitrate-containing fertilizers were not asignificant source of riverine nitrate inwatersheds with significant agricultural andurban land use. Although complementary studiesindicate that in-stream denitrification wassignificant in all rivers, the isotopiccomposition of riverine nitrate sampled at theoutlet of the 16 watersheds did not provideevidence for denitrification in the form ofelevated 15Nnitrate and18Onitrate values. Relativelylow isotopic enrichment factors for nitrogenand oxygen during in-stream denitrification andcontinuous admixture of nitrate from theabove-described sources are thought to beresponsible for this finding.  相似文献   

5.
Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The 13C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (13C between-25.3 and-27.8) were significantly less depleted in 13C than needles (13C between-27.3 and-29.1), and 13C in twigs increased consistently with age. The 15N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles 15N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in 15N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. 15N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. 15N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The 15N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed.  相似文献   

6.
T. H. E. Heaton 《Oecologia》1987,74(2):236-246
Summary Data are presented for the 15N/14N ratios of 140 indigenous terrestrial plants from a wide variety of natural habitats in South Africa and Namibia. Over much of the area, from high-rainfall mountains to arid deserts, the 15N values of plants lie typically in the range -1 to +6; with no evident differences between C3 plants and C4 grasses. There is a slight correlation between 15N and aridity, but this is less marked than the correlation between the 15N values of animal bones and aridity. At coastal or saline sites, however, the mean 15N values for plants are higher than those at nearby inland or non-saline sites-e.g.: arid Namib coast (10 higher than inland Namib); wet Natal beach (5 higher than inland Natal); saline soils 500 km from coast (4 higher than non-saline soils). High values were also found at one site where there were no marked coastal or saline influences. These environmental effects on the isotopic composition of plants will extend upwards to the animals and humans they support. They therefore have important consequences for the use of nitrogen isotope data in the study of the dietary habits and trophic structures of modern and prehistoric communities.  相似文献   

7.
The measurement of natural 15N abundance is a well-established technique for the identification and quantification of biological N2 fixation in plants. Associative N2 fixing bacteria have been isolated from sugarcane and reported to contribute potentially significant amounts of N to plant growth and development. It has not been established whether Australian commercial sugarcane receives significant input from biological N2 fixation, even though high populations of N2 fixing bacteria have been isolated from Australian commercial sugarcane fields and plants. In this study, 15N measurements were used as a primary measure to identify whether Australian commercial sugarcane was obtaining significant inputs of N via biological N2 fixation. Quantification of N input, via biological N2 fixation, was not possible since suitable non-N2 fixing reference plants were not present in commercial cane fields. The survey of Australian commercially grown sugarcane crops showed the majority had positive leaf 15N values (73% >3.00, 63% of which were >5.00), which was not indicative of biological N2 fixation being the major source of N for these crops. However, a small number of sites had low or negative leaf 15N values. These crops had received high N fertiliser applications in the weeks prior to sampling. Two possible pathways that could result in low 15N values for sugarcane leaves (other than N2 fixation) are proposed; high external N concentrations and foliar uptake of volatilised NH3. The leaf 15N value of sugarcane grown in aerated solution culture was shown to decrease by approximately 5 with increasing external N concentration (0.5–8.0 mM), with both NO3 and NH4 + nitrogen forms. Foliar uptake of atmospheric NH3 has been shown to result in depleted leaf 15N values in many plant species. Acid traps collected atmospheric N with negative 15N value (–24.45±0.90) from above a field recently surface fertilised with urea. The 15N of leaves of sugarcane plants either growing directly in the soil or isolated from soil in pots dropped by 3.00 in the same field after the fertiliser application. Both the high concentration of external N in the root zone (following the application of N-fertilisers) and/or subsequent foliar uptake of volatilised NH3 could have caused the depleted leaf 15N values measured in the sugarcane crops at these sites.  相似文献   

8.
Natural abundance of 15N in tropical plants with emphasis on tree legumes   总被引:6,自引:0,他引:6  
Natural abundance of 15N ( 15N) of leaves harvested from tropical plants in Brazil and Thailand was analyzed. The 15N values of non-N2-fixing trees in Brazil were +4.5±1.9, which is lower than those of soil nitrogen (+8.0±2.2). In contrast, mimosa and kudzu had very low 15N values (–1.4+0.5). The 15N values of Panicum maximum and leguminous trees, except Leucaena leucocephala, were similar to those of non-N2-fixing trees, suggesting that the contribution of fixed N in these plants is negligible. The 15N values of non-N2-fixing trees in Thailand were +4.9±2.0. Leucaena leucocephala, Sesbania grandiflora, Casuarina spp. and Cycas spp. had low 15N values, close to the value of atmospheric N2 (0), pointing to a major contribution of N2 fixation in these plants. Cassia spp. and Tamarindus indica had high 15N values, which confirms that these species are non-nodulating legumes. The 15N values of Acacia spp. and Gliricidia sepium and other potentially nodulating tree legumes were, on average, slightly lower than those of non-N2-fixing trees, indicating a small contribution of N2 fixation in these legumes.  相似文献   

9.
In natural ecosystems, differences often exist in the relative abundanceof stable S isotopes (°34S) that can provide clues as tothe source, nature, and cycling of S. Values of °34S inprecipitation, throughfall, soils, soil solution, and stream waters weremeasured at the Hubbard Brook Experimental Forest (HBEF), New Hampshire.Values of °34S in precipitation and throughfall weresimilar to each other but differed seasonally. Precipitation°34S values were higher in the dormant season[°34S = 5.9±0.6 (17)][Mean + SE(N)]than in the growing season [°34S = 5.0±0.6(40)] but throughfall growing-season values were higher[°34S = 5.6±0.6(68)] than for the dormantseason [°34S = 4.9±0.7 (9)]. Different treespecies did not affect throughfall °34S values. In soilsolution, °34S values were higher in the growing season(°34S = 8.9±2.8; 8.8±1.7;and 4.0±0.6 for Oa, Bh, and Bs horizons, respectively) thanin the dormant season (°34S = 5.6±1.5;3.7±2.4; and 3.4±1.2 for Oa, Bh, and Bshorizons, respectively). These seasonal differences in°34S were probably caused by biological isotopicfractionation. The °34S values in streams were generally2 lower and more variable than those in precipitation andthroughfall, suggesting fractionation and/or different isotopic sources inthe soil.  相似文献   

10.
Liu  X.Q.  Wang  R.Z.  Li  Y.Z. 《Photosynthetica》2004,42(3):339-344
Photosynthetic pathway types, based on 13C measurements, were determined for 125 species in 95 genera and 32 families growing in rangelands from Inner Mongolia. Of the total species, 4 species from 3 genera and 2 families had C4 photosynthesis (2 species in Gramineae and 2 in Chenopodiaceae) and 118 species from 90 genera and 31 families had C3 photosynthesis. The number of C4 species differed significantly among four rangeland sites, 4 species in desert, 3 species in steppe, but no C4 species were identified in meadow and dune. Six species [e.g. Agriophyllum arenarium Bieb., Bassia dasyphylla O. Kuntze, Saussurea japonica (Thunb.) DC.] earlier identified as C4 species using the enzyme ratio method were found as C3 species using the carbon isotope ratios (13C). Hence the enzyme ratio method for C3 and C4 identification may not always be reliable. The 13C values of 3 species of Crassulaceae, which had been considered as CAM species, differed remarkably [–25.79 for Sedum aizoon L., –24.42 for Osostachys fimbriatus (Turcz.) Berger, and –16.97 for O. malacophyllus (Pall.) Fisch], suggesting that the use of 13C method as a diagnosis for CAM photosynthetic pathway type may not always be reliable and supplementary measurements are needed.  相似文献   

11.
Cyanobacterial mats (CBM) are important components of wetland ecosystems in limestone-based regions of the Caribbean. During two sampling periods (July 1999 and January 2000) we measured N2-fixation in samples from 23 different marshes simultaneously with measurements of relevant environmental factors. Samples were evaluated for abundance of five groups of cyanobacteria: (1) Leptolyngbya, (2) Oscillatoria, (3) Chroococcales, (4) Nostoc-& Stigonematales, and (5) dead sheaths. Differences in nitrogen fixation, expressed as nitrogenase activity in nmol C2H4 cm–2 h–1, were best explained by the proportion of heterocyst-forming cyanobacteria. The samples were analyzed for the natural abundance of 15N. 15N values ranged from –1.99 to 11.44 and were strongly negatively correlated with N2-fixation. With all data included, 15N was also strongly correlated with nitrates in water. With the samples from Little Belize (high nitrate content marshes) excluded, the effect of nitrate became insignificant. N2-fixation predicted from 15N measured on an independent data set from September 2000 was moderately accurate (r2 = 0.68, 0.52 and 0.54 for predictions based on July 1999, January 2000 and combined data sets, respectively). When individual sample sets were divided into two groups with 15N < 2 and 15N > 2, the two groups were always highly significantly different in terms of their N2-fixation. The presented evidence suggests that 15N can be used as a reliable indicator of N2-fixation by CBM.  相似文献   

12.
Eriksen  J.  Høgh-jensen  H. 《Plant and Soil》1998,205(1):67-76
Biological N2 fixation in clover is an important source of N in low external-N input farming systems. Using the natural 15N-abundance method, variations in N2 fixation were investigated in grazed and mowed plots of a ryegrass/white clover field. Ryegrass 15N varied considerably, from 0.2 to 5.6 under mowed conditions and from –3.3 to 11.6 under grazed conditions. Variations in 15N white clover were lower than in ryegrass, especially in the mowed plots (SE = 0.05, n = 20). The variations in the percentage of nitrogen derived from the atmosphere (%Ndfa) in white clover were highest in the grazed plots where it ranged from 12 to 96% (mean = 64%) compared with the mowed plots where it ranged from 64 to 92% (mean = 79%). Thus, the N2 fixation per unit white clover DM in the grazed ley was lower and more variable than under mowing conditions.Urine from dairy cows equivalent to 0, 200, 400 and 800 kg N ha-1 was applied to a ryegrass/white clover plot 6, 4 or 2 weeks before harvest. Without urine application 15N of ryegrass was positive. By increasing urine application (15N = –1) two weeks before sampling, the 15N of ryegrass decreased strongly to about –7 (P < 0.001). However, this effect was only observed when urine was applied two weeks before sampling. When applying 800 kg N four and six weeks before sampling, 15N in ryegrass was not significantly different from the treatment without urine application. White clover 15N was unaffected by whatever changes occurred in 15N of the plant-available soil N pool (reflected in 15N of ryegrass). This indicates that within the time span of this experiment, N2 fixation per unit DM was not affected by urine. Therefore, newly deposited urine may not be the main contributing factor to the variation in %Ndfa found in the grazed fields. This experiment suggested that the natural abundance method can be applied for estimating %Ndfa without disturbance in natural animal-grazed systems.  相似文献   

13.
Stable carbon (13C) and nitrogen (15N) isotopes were used to elucidate primary food sources and trophic relationships of organisms in Khung Krabaen Bay and adjacent offshore waters. The three separate sampling sites were mangroves, inner bay and offshore. The 13C values of mangrove leaves were –28.2 to –29.4, seagrass –10.5, macroalgae –14.9 to –18.2, plankton –20.0 to –21.8, benthic detritus –15.1 to –26.3, invertebrates –16.5 to –26.0, and fishes –13.4 to –26.3. The 15N values of mangrove leaves were 4.3 to 5.7, seagrass 4.3, macroalgae 2.2 to 4.4, plankton 5.7 to 6.4 , benthic detritus 5.1 to 5.3, invertebrates 7.2 to 12.2 , and fishes 6.3 to 15.9. The primary producers had distinct 13C values. The 13C values of animals collected from mangroves were more negative than those of animals collected far from shore. The primary carbon sources that support food webs clearly depended on location. The contribution of mangroves to food webs was confined only to mangroves, but a mixture of macroalgae and plankton was a major carbon source for organisms in the inner bay area. Offshore organisms clearly derived their carbon through the planktonic food web. The 15N values of consumers were enriched by 3–4 relative to their diets. The 15N data suggests that some of aquatic animals had capacity to change their feeding habits according to places and availability of foods and as a result, individuals of the same species could be assigned to different trophic levels at different places.  相似文献   

14.
Variation in stable nitrogen isotope ratios (15N) was assessed for plants comprising two wetland communities, a bog-fen system and a flood plain, in central Japan. 15N of 12 species from the bog-fen system and six species from the flood plain were remarkably variable, ranging from –5.9 to +1.1 and from +3.1 to +8.7, respectively. Phragmites australis exhibited the highest 15N value at both sites. Rooting depth also differed greatly with plant species, ranging from 5cm to over 200cm in the bog-fen system. There was a tendency for plants having deeper root systems to exhibit higher 15N values; plant 15N was positively associated with rooting depth. Moreover, an increasing gradient of peat 15N was found along with depth. This evidence, together with the fact that inorganic nitrogen was depleted under a deep-rooted Phragmites australis stand, strongly suggests that deep-rooted plants actually absorb nitrogen from the deep peat layer. Thus, we successfully demonstrated the diverse traits of nitrogen nutrition among mire plants using stable isotope analysis. The ecological significance of deep rooting in mire plants is that it enables those plants to monopolize nutrients in deep substratum layers. This advantage should compensate for any consequential structural and/or physiological costs. Good evidence of the benefits of deep rooting is provided by the fact that Phragmites australis dominates as a tall mire grass.  相似文献   

15.
The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in 13C values along a rainfall gradient (50–600 mm) and in different habitat conditions. However, there are significant differences in the 13C values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest 13C values (–11.7 ) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower 13C values (–13.4 ) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (–12.5 ) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative 13C values than PCK species and 13C values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, 13C values decreased from –11 in the inland region (600 mm precipitation) to –15 near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.  相似文献   

16.
E. Medina  P. Minchin 《Oecologia》1980,45(3):377-378
Summary The contribution of soil respiration to the photosynthesis of the shade flora in the Amazon forest was evaluated by measuring the 13C values of leaves collected at different levels in two forest communities. Canopy leaves have an average 13C of-30.5 in the podsol forest and-28.7 in the laterite forest. Leaves from plants in the lower forest strata have a significantly lower value of-35.2 in the podsol forest and-34.3 in the laterite forest.Mailing address of the first author: Before May 31, 1980: Department of Biological Sciences, Stanford University, Stanford, California 94305 USA. After May 31: Centro de Ecologia, IVIC Aptdo. 1827. Caracas, Venezuela  相似文献   

17.
Data from tagging studies and stable isotope ratio analyses (18O and 13C) in otoliths of tagged Pacific halibut, Hippoglossus stenolepis, provided unique information about halibut distribution and area migration. The 18O values of otoliths of individual halibut tagged in the Bering Sea and the Gulf of Alaska ranged from –0.5 to +1.0 VPDB (Vienna Peedee belemnite) in the first few years, but gradually increased to 2.0–2.5 VPDB when these tagged fish were recaptured as adults in waters off British Columbia. Similar isotopic variations were found in 13C. Comparison of isotopic composition from the age-1 halibut (i.e., aragonite samples taken from the first annulus of otoliths) and the adult (ages 8) indicated that the ocean conditions between the Bering Sea and the northeast Pacific were markedly different over the tagging period, but the area boundaries between the Gulf of Alaska and British Columbia were not clear. We concluded that stable isotopic records in otoliths of tagged Pacific halibut were informative and particularly useful for details of subsequent movement of halibut between release and recovery.  相似文献   

18.
A combination of stable isotope studies and 14Cdating were used to identify the main sources andprocesses controlling streamwater DOC and TIC in atemperate non-forested watershed. 13Cvalues for terrestrial (–24.9 to –29.1) and aquatic(–30.5 to –33.5) plants were similar to valuesreported in the literature for similar ecosystems.13C values for DOC in soil solution andstreamwater were consistent with soil and terrestrialvegetation, indicating that the terrestrial ecosystemis the dominant source of aquatic DOC in thiswatershed. 13C values of soil atmosphereCO2 (–17.2 to –25.2) were slightly lessnegative than would be expected for production viaaerobic soil microbial decomposition and rootrespiration. There was a close correspondence between13C values (–15.5 to –21.5) forstreamwater TIC and soil atmospheric CO2 in thecentral part of the catchment where the stream drainsCO2-rich peats. 14C dating showed thatalthough peat has been accumulating in the watershedfor at least 2700 years, DOC in soil pore water andstreamwater contains carbon of predominantly recentorigin (post-AD 1955).  相似文献   

19.
The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in 15N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in 15N was found in the mysid. The annual averages of 15N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of15N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of 15N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.  相似文献   

20.
Culture experiments were carried out with Acropora sp. (a branching scleractinian coral) in seawater at two pCO2 conditions (438 and 725 µatm) and two temperatures (25 and 28 °C) in order to establish the pH and temperature dependence of the boron isotopic composition of the skeleton. A clear pCO2 effect, but no temperature effect, on the coral boron isotope composition is seen. For corals cultured at normal pCO2 (438 µatm), the 11B of the skeleton was 24.0±0.2 at 25 °C, and 23.9±0.3 at 28 °C. The values of 11B measured for corals cultured at higher pCO2 (725 µatm) were lower: 22.5±0.1, and 22.8±0.1 at 25 and 28 °C, respectively. The 11B of corals cultivated at both high and normal pCO2 conditions are consistent with a dominant pH control, and are very close to that calculated from theoretical considerations. Thus, the corals do not seem to significantly alter ambient seawater for calcification with respect to pH. Co-variation between boron and carbon isotope values is explored.Communicated by: Guest Editor A. Grottoli  相似文献   

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