γδ T-cell receptor repertoire in human peripheral blood and thymus

T-cell clones expressing the T-cell receptor (Tcr) were generated from peripheral blood lymphocytes (PBLs) and from a thymus sample. In the panel of ten thymus-derived clones, four Tcr phenotypes [as defined by the reaction of monoclonal antibodies (mAbs) directed against known V and V regions] were identified. All the clones lacked expression of the V3 V region, while seven clones were V1+ . V1 was found in combination with V9 or with undefined VVregions. In addition, two other Tcr phenotypes were identified on these clones: V9⁺ V1^– V3^– and V9^– V1^– V3^– One of the clones expressed CD4 and another was CD8positive. The remaining clones were CD4^– CD8^–. In the panel of 76 PBL-derived, Tcr-bearing clones, five Tcr phenotypes could be identified. In contrast to the thymus-derived clones, 30% of the clones were V3⁺ whereas V1 was expressed by a minority of the clones only. One clone was CD4-positive and approximately 30% of the clones were CD8-positive. Four of the five mAb-defined Tcr phenotypes could be identified on both thymus and PBL-derived T-cell clones. However, biochemical analysis of the Tcrs demonstrates differences in the usage of Ct- and C2-encoded y chains by T cells derived from the thymus and PBLs. The results therefore indicate that, at the clonal level, similarities and differences exist between the Tcr repertoires expressed in the thymus and by PBLs. Furthermore, they indicate that combinatorial Tcr heterogeneity is larger than has so far been described. The receptor diversity, combined with the potential of Tcr+ cells to express CD4 or CD8, indicates that these cells are a heterogeneous population that might mediate a number of immune functions.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

Water and nitrogen dynamics in an arid woodland

Arid environments are characterized by spatial and temporal variation in water and nitrogen availability. differences in ¹⁵N and D of four co-occurring species reveal contrasting patterns of plant resource acquisition in response to this variation. Mineralization potential and nitrogen concentration of surface soils associated with plant canopies were greater than inter-canopy locations, and values decreased with increasing depth in both locations. Mineralization potential and nitrogen concentration were both negatively correlated with soil ¹⁵N. The spatial variation in soil ¹⁵N caused corresponding changes in plant ¹⁵N such that plant ¹⁵N values were negatively correlated with nitrogen concentration of surface soils. Plants occurring on soils with relatively high nitrogen concentrations had lower ¹⁵N, and higher leaf nitrogen concentrations, than plants occurring on soils with relatively low nitrogen concentrations. Two general temporal patterns of water and nitrogen use were apparent. Three species (Juniperus, Pinus andArtemisia) relied on the episodic availability of water and nitrogen at the soil surface. ¹⁵N values did not vary through the year, while xylem pressure potentials and stem-water D values fluctuated with changes in soil moisture at the soil surface. In contrast,Chrysothamnus switched to a more stable water and nitrogen source during drought. ¹⁵N values ofChrysothamnus increased throughout the year, while xylem pressure potentials and stem-water D values remained constant. The contrasting patterns of resource acquisition have important implications for community stability following disturbance. Disturbance can cause a decrease in nitrogen concentration at the soil surface, and so plants that rely on surface water and nitrogen may be more susceptible than those that switch to more stable water and nitrogen sources at depth during drougnt.     

Comparisons of δ13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants

Summary The ¹³C values of submerged aquatic plants from contrasting but relatively defined habitats, and the ¹³C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the ¹³C values of dissolved inorganic carbon in the water were also measured. Plant ¹³C values in the vicinity of-40 to-50 were found in rapidly flowing spring waters with carbonate ¹³C values of-16 to-21, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO₂ via RuP₂ carboxylase. Plant ¹³C values in the vicinity of-10 to-15 in sluggish water with carbonate ¹³C values of about-5 were observed, consistent with the notion that boundary layer diffusion and/or HCO₃ ^- uptake may determine the ¹³C value of submerged aquatic plants in these circumstances. Comparisons of ¹³C values of the same or related species growing in waters of similar carbonate ¹³C value but different flow rates confirmed this view; more negative ¹³C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the ¹³C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The ¹³C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO₂, as opposed to atmospheric carbon. The contributions of these variations in ¹³C of the carbon source, and of isotope fractionation in diffusion, to the ¹³C value of submerged parts of dimorphic plants is discussed.     

Analysis of primary food sources and trophic relationships of aquatic animals in a mangrove-fringed estuary,Khung Krabaen Bay (Thailand) using dual stable isotope techniques

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.     

Leaf thickness and carbon isotope composition in the Crassulaceae

Summary Measurements of leaf thickness and ¹³C value were obtained for twenty species and three intergeneric hybrids of the Crassulaceae. The data include plants growing in their native habitats and also in greenhouse cultivation. There is a strong relationship between leaf thickness and leaf ¹³C values. The plants with the thickest leaves of ca. 7 to 11 mm had ¹³C values ranging from -11.5 to -13.8. Plants with leaves that were thinner than 2.0 mm all had ¹³C values that were more negative than -23. Plants having intermediate leaf thickness possessed intermediate ¹³C values. The leaf tissue of four genotypes spanning the range of leaf thicknesses all exhibited a two-fold or greater nocturnal increase in titratable acidity. It appears that the differences in leaf thickness and ¹³C values among the tested species are genetically determined.     

Carbon and nitrogen stable isotope ratios of deposit-feeding polychaetes in the Nanakita River Estuary, Japan

Two types of deposit-feeding polychaetes, Neanthes japonica and Notomastus sp., and their surrounding sediments were collected from the Nanakita River Estuary and a small brackish lagoon (Gamõ Lagoon) in northeastern Japan. The samples were examined using stable isotope analysis to assess the site specific feeding mode of the animals and their trophic status. N. japonica is a surface deposit-feeder and Notomastus sp. is a subsurface deposit-feeder. In the estuary, the sedimentary ⁵N tended to become isotopically heavier from the upper estuary (2.0 3.9) to the river mouth (4.3 6.2), while sedimentary organic ¹³C constant value (–26.8 –24.4, average –25.6) throughout the river estuary. The ¹³C values of N. japonica were similar to those of the surrounding sediment in the upper estuary, whereas in the lower estuary, N. japonica had a heavier ¹³C value than the surrounding sediment. The ¹³C and dg ¹⁵N values indicated that the carbon, but not the nitrogen, of N. japonica was derived from upland plants in the upper estuary. In the lower estuary, a significant fraction of carbon of N. japonica was derived from phytoplankton. Notomastus sp. exhibited heavier ¹³C values than the surrounding surface sediment throughout the estuary and had heavier ¹³C values than N. japonica in the same location. These results suggest selective utilization of sedimentary carbon by those animals following bacterial processing and subsequent fractionation. The difference in ¹⁵N between sedimentary organics and corresponding polychaetes was 5 ± 1 and rather higher than 3.4 ± 1.1 expected for normal trophic effects in other animals.     

Spatial and temporal variation in carbon isotope discrimination in prairie graminoids

We present the results of a 5-year examination of variation in the stable carbon isotope composition () of three C₃ graminoid species from a Sandhills prairie: Agropyron smithii, Carex heliophila and Stipa comata. Although consistent species-specific patterns for mean were seen, there was also significant and substantial among-year and within-season variation in . A smaller contribution to variation in came from topographic variation among sampling sites. Effects of species, year, season and topography contribute to variation in in an additive manner. An association between climate and exists that is consistent with previous work suggesting that reflects the interplay between photosynthetic gas exchange and plant water relations. Within the growing season, the time over which integrates plant response to the environment ranges from days to months.     

Skeletal isotope microprofiles of growth perturbations in<Emphasis Type="Italic"> Porites</Emphasis> corals during the 1997–1998 mass bleaching event

Severe coral bleaching occurred throughout the tropics in 1997/98. We report high-resolution skeletal oxygen isotope (¹⁸O) and carbon isotope (¹³C) microprofiles for bleached corals from Pandora Reef, Great Barrier Reef, and Ishigaki Island, Japan, in order to examine the ability of Porites corals to record clear signals of bleaching. Analysis of the annual cycle in ¹⁸O revealed abrupt reductions in skeletal extension immediately after the 1997–98 summer temperature maximum, indicating that bleaching inhibits coral calcification. Skeletal ¹³C in the Ishigaki corals showed lower values during bleaching, indicating depressed coral metabolism associated with a reduction in calcification. In contrast, microprofiles of skeletal ¹³C from the shaded sides of Pandora Reef corals exhibited little change, possibly because algal photosynthesis was already slow prior to bleaching, thus subduing the ¹³C-response to bleaching. Comparison of ¹⁸O microprofiles from bleached corals with instrumental temperature records showed that Porites corals can recover following 5 months with little skeletogenesis. The results indicate that isotopic microprofiling may be the key to identifying gaps in coral growth that are diagnostic of past bleaching events. We have tested this hypothesis using blue UV fluorescent bands to guide us to coral skeleton where isotope microprofiling identifies bleaching events in 1986, 1989, and 1990. These events, detected by proxy, suggest that coral bleaching may have occurred more commonly on Ishigaki Island than previously recorded.     

Stable carbon and oxygen isotopic compositions of recent charophyte oosporangia and water from Malham Tarn,U.K.: palaeontological implications

Charophyte oosporangia and water samples from a highly calcareous lake were measured for stable carbon and oxygen isotopic composition. The time period over which the oosporangia calcify is short, thus any biochemical relationship between the water and oosporangia"s calcite represents only one time window (late Summer in Malham Tam). This important temporal restraint must also apply to interpretations of all fossil material measured. The ¹⁸O_c of the charophyte oosporangia is deduced to be in equilibrium with the ¹⁸O of the water for a given temperature. The ¹³ C_c of the charophyte oosporangia was approximately 2.5 per mil lower than the ¹³C_DIC in the water we measured. With the release Of CO₂ with phosphoric acid from the charophyte oosporangia, there was no significant difference in the ¹⁸O_c values obtained, regardless of whether or not the carbonate was separated from the organic center, however ¹³C_c values were marginally lower for carbonate plus organic center measurements. Our results indicate that fossil charophyte gyrogonites can be used to elucidate the geochemistry of the ancient water body in which they lived.     

Selective feeding by larval dytiscids (Coleoptera:Dytiscidae) and effects of fish predation on upper littoral zone macroinvertebrate communities of arctic lakes

Carbon and nitrogen stable isotopic data from the primary producers in mangrove ecosystems are needed to investigate trophic links and biogeochemical cycling. Compared with other mangrove species (e.g. Rhizophora mangle) very few measurements have been conducted on the white mangrove, Laguncularia racemosa. The carbon and nitrogen stable isotopic and elemental compositions of L. racemosa were analyzed and compared from Florida and Belize. ¹³C values of L. racemosa from Florida (mean = –26.4) were slightly higher than those from Twin Cays, Belize (mean = -27.4), which may be due to higher salinity in some parts of the Florida site. There was no difference between the ¹⁵N values from L. racemosa from these two sites (Florida mean = 0.6; Belize mean = 0.3), which are indicative of nitrogen derived from nitrogen fixation in a planktonic marine system. However, higher ¹⁵N values from L. racemosa at Man of War Cay in Belize (11.4 and 12.3), which is fertilized by roosting marine birds (14.0), illustrate that L. racemosa can sensitively reflect alternative nitrogen sources. Although the isotopic data could not distinguish between Avicennia germinans, R. mangle and L. racemosa in Belize the L. racemosa had considerably higher C/N ratios (46.5 – 116.1) compared with the Florida samples (42.2 – 76.0) or the other mangrove species. Unlike some previous findings from R. mangle, substrate characteristics (e.g. salinity, NH₄ ⁺, and H₂S) were not related to the isotopic or elemental composition of L. racemosa. ¹³C, ¹⁵N and C/N were analyzed for ecosystem components from L. racemosa habitats at Twin Cays, including other plants (e.g. R. mangle, A. germinans and seagrass), detritus, microbial mats and sediments. Results from mass-balance calculations show that mangrove detritus composes very little of the sediment, which is principally composed of microbial biomass (80 – 90%). Detritus at some sites is also influenced by sources other than that from L. racemosa, including seagrass leaves.     

Intracellular sites of the synthesis of sweet potato mitochondrial F1ATPase subunits

Summary Five subunits (-, -, -, - and -subunits) of the six -and -subunits) in the F₁ portion (F₁ATPase) of sweet potato (Ipomoea batatas) mitochondrial adenosine triphosphatase were isolated by an electrophoretic method. The - and -subunits were not distinguishable immunologically but showed completely different tryptic peptide maps, indicating that they were different molecular species. In vitro protein synthesis with isolated sweet potato root mitochondria produced only the -subunit when analyzed with anti-sweet potato F₁ATPase antibody reacting with all the subunits except the -subunit. Sweet potato root poly(A)⁺RNA directed the synthesis of six polypeptides which were immunoprecipitated by the antibody: two of them immunologically related to the -subunit and the others to the - and -subunits. We conclude that the -subunit of the F₁ATPase is synthesized only in the mitochondria and the -, - and -subunits are in the cytoplasm.     

Fine-scale movement and assimilation of carbon in saltmarsh and mangrove habitat by resident animals

Despite theories of large-scale movement and assimilation of carbon in estuaries, recent evidence suggests that in some estuaries much more limited exchange occurs. We measured the fine-scale movement and assimilation of carbon by resident macroinvertebrates between adjacent saltmarsh and mangrove habitats in an Australian estuary using ¹³C analysis of animals at different distances into adjacent patches of habitat. ¹³C values of crabs (Parasesarma erythrodactyla –15.7 ± 0.1, Australoplax tridentata –14.7 ± 0.1) and slugs (Onchidina australis –16.2 ± 0.3) in saltmarsh closely matched that of the salt couch grass Sporobolus virginicus (–15.5 ± 0.1). In mangroves, ¹³C values of crabs (P. erythrodactyla –22.0 ± 0.2, A. tridentata –19.2 ± 0.3) and slugs (–19.7 ± 0.3) were enriched relative to those of mangroves (–27.9 ± 0.2) but were more similar to those of microphytobenthos (–23.7 ± 0.3). The ¹³C values of animals across the saltmarsh-mangrove interface fitted a sigmoidal curve, with a transition zone of rapidly changing values at the saltmarsh-mangrove boundary. The width of this transition indicated that the movement and assimilation of carbon is limited to between 5 and 7 m. The ¹³C values of crabs and slugs, especially those in saltmarsh habitat, clearly indicate that the movement and assimilation of carbon between adjacent saltmarsh and mangrove habitat is restricted to just a few metres, although some contribution from unmeasured sources elsewhere in the estuary is possible. Such evidence demonstrating the extent of carbon movement and assimilation by animals in estuarine habitats is useful in determining the spatial arrangement of habitats needed in marine protected areas to capture food web processes.     

Carbon isotope composition in relation to leaf gas exchange and environmental conditions in Hawaiian Metrosideros polymorpha populations

Summary Carbon isotope composition, photosynthetic gas exchange, and nitrogen content were measured in leaves of three varieties of Metrosideros polymorpha growing in sites presenting a variety of precipitation, temperature and edaphic regimes. The eight populations studied could be divided into two groups on the basis of their mean foliar ¹³C values, one group consisting of three populations with mean ¹³C values ca.-26 and another group with ¹³C values ca.-28. Less negative ¹³C values appeared to be associated with reduced physiological availability of soil moisture resulting from hypoxic conditions at a poorly drained high elevation bog site and from low precipitation at a welldrained, low elevation leeward site. Gas exchange measurements indicated that foliar ¹³C and intrinsic wateruse efficiency were positively correlated. Maximum photosynthetic rates were nearly constant while maximum stomatal conductance varied substantially in individuals with foliar ¹³C ranging from-29 to-24. In contrast with the patterns of ¹³C observed, leaf nitrogen content appeared to be genetically determined and independent of site characteristics. Photosynthetic nitrogenuse efficiency was nearly constant over the range of ¹³C observed, suggesting that a compromise between intrinsic water- and N-use efficiency did not occur. In one population variations in foliar ¹³C and gas exchange with leaf cohort age, caused the ratio of intercellular to atmospheric partial pressure of CO₂ predicted from gas exchange and that calculated from ¹³C to be in close agreement only in the two youngest cohorts of fully expanded leaves. The results indicated that with suitable precautions concerning measurement protocol, foliar ¹³C and gas exchange measurements were reliable indicators of potential resource use efficiency by M. polymorpha along environmental gradients.     

The skeletal isotopic composition as an indicator of ecological and physiological plasticity in the coral genus<Emphasis Type="Italic"> Madracis</Emphasis>

Three species of the reef coral genus Madracis display skeletal isotopic characteristics that relate to depth, colony topography, and consequently to coral physiology. The joint interpretation of skeletal ¹³C and ¹⁸O provides information on the ecological plasticity and adaptation to depth of a coral species. Isotopic results are most easily understood in terms of kinetic effects, which reduce both ¹⁸O and ¹³C below isotopic equilibrium values, and metabolic effects, which only influence the skeletal ¹³C. Madracis mirabilis is adapted to depths shallower than 20 m, and shows the greatest range in kinetic effects and the strongest metabolic ¹³C enrichments caused by symbiont photosynthesis. Madracis formosa lives deeper than 40 m, and shows a reduced range of kinetic effects and relatively weak metabolic ¹³C enrichments. Madracis pharensis inhabits depths from 5 to >60 m, and does not attain the strength of kinetic effects of either of the other two species, apparently because it is not quite as well adapted to rapid growth at either extreme.     

Leaf 15N abundance of subarctic plants provides field evidence that ericoid,ectomycorrhizal and non-and arbuscular mycorrhizal species access different sources of soil nitrogen

The natural abundance of the nitrogen isotope 15, ¹⁵N, was analysed in leaves of 23 subarctic vascular plant species and two lichens from a tree-line heath at 450 m altitude and a fellfield at 1150 m altitude close to Abisko in N. Sweden, as well as in soil, rain and snow. The aim was to reveal if plant species with different types of mycorrhizal fungi also differ in their use of the various soil N sources. The dwarf shrubs and the shrubs, which in combination formed more than 65% of the total above-ground biomass at both sites, were colonized by ericoid or ectomycorrhizal fungi. Their leaf ¹⁵N was between–8.8 and–5.5 at the heath and between–6.1 and –3.3 at the fellfield. The leaf ¹⁵N of non- or arbuscular mycorrhizal species was markedly different, ranging from –4.1 to –0.4 at the heath, and from –3.4 to+2.2 at the fellfield. We conclude that ericoid and ectomycorrhizal dwarf shrubs and shrubs utilize a distinct N source, most likely a fraction of the organic N in fresh litter, and not complexed N in recalcitrant organic matter. The latter is the largest component of soil total N, which had a ¹⁵N of –0.7 at the heath and +0.5 at the fellfield. Our field-based data thus support earlier controlled-environment studies and studies on the N uptake of excised roots, which have demonstrated protease activity and amino acid uptake by ericoid and ectomycorrhizal tundra species. The leaves of ectomycorrhizal plants had slightly higher ¹⁵N (fellfield) and N concentration than leaves of the ericoids, and Betula nana, Dryas octopetala and Salix spp. also showed NO _inf3 ^sup- reductase activity. These species may depend more on soil inorganic N than the ericoids. The ¹⁵N of non- or arbuscular mycorrhizal species indicates that the ¹⁵N of inorganic N available to these plants was higher than that of average fresh litter, probably due to high microbial immobilization of inorganic N. The ¹⁵N of NH _inf4 ^sup+ -N was +12.3 in winter snow and +1.9 in summer rain. Precipitation N might be a major contributer in species with poorly developed root systems, e.g. Lycopodium selago. Our results show that coexisting plant species under severe nutrient limitation may tap several different N sources: NH _inf4 ^sup+ , NO _inf3 ^sup- and organic N from the soil, atmospheric N₂, and N in precipitation. Ericoid and ectomycorrhizal fungi are of major importance for plant N uptake in tundra ecosystems, and mycorrhizal fungi probably exert a major control on plant ¹⁵N in organic soils.     

Alterations in protein kinase C isoenzyme expression and autophosphorylation during the progression of pressure overload-induced left ventricular hypertrophy

Cardiomyocytes express several isoenzymes of protein kinase C (PKC), which as a group have been implicated in the induction of left ventricular hypertrophy (LVH) and its transition to heart failure. Individual PKC isoenzymes also require transphosphorylation and autophosphorylation for enzymatic activity. To determine whether PKC isoenzyme expression and autophosphorylation are altered during LVH progression in vivo, suprarenal abdominal aortic coarctation was performed Sprague-Dawley rats. Quantitative Western blotting was performed on LV tissue 1, 8 and 24 weeks after aortic banding, using antibodies specific for total PKC, PKC and PKC, and their C-terminal autophosphorylation sites. Aortic banding produced sustained hypertension and gradually developing LVH that progressed to diastolic heart failure over time. PKC levels and autophosphorylation were not significantly different from sham-operated controls during any stage of LVH progression. PKC expression levels were also unaffected during the induction of LVH, but increased 3.2 ± 0.8 fold during the transition to heart failure. In addition, there was a high degree of correlation between PKC levels and the degree of LVH in 24 week banded animals. However, autophosphorylated PKC was not increased at any time point. In contrast, PKC autophosphorylation was increased prior to the development of LVH, and also during the transition to heart failure. The increased PKC autophosphorylation in 1 week banded rats was not accompanied by an increase in total PKC, whereas total PKC levels were markedly increased (6.0 ± 1.7 fold) in 24 week banded animals. Furthermore, both phosphorylated and total PKC levels were highly correlated with the degree of LVH in 24 week banded rats. In summary, we provide indirect evidence to indicate that PKC may be involved in the induction of pressure overload LVH, whereas both PKC and PKC may be involved in the transition to heart failure.     

Using stable hydrogen and oxygen isotope measurements of feathers to infer geographical origins of migrating European birds

Successful application of stable-hydrogen isotope measurements (D_f) of feathers to track origins of migratory birds and other wildlife requires a fundamental understanding of the correlation between D_f and deuterium patterns in rainfall (D_p) over continental scales. A strong correlation between D_p and D_f has been confirmed for birds and insects in North America, but not yet for other continents. Here, we compare D_f data from resident European birds to new D_p basemaps for Europe. Three maps, representing growing-season and mean annual D_p estimates from an elevation-explicit, detrended interpolation model and growing-season D_p estimates from simple Kriging, all indicate that strong isotope gradients occur across Europe with a general depletion occurring in a northeast direction. The feather data, representing 141 individuals of 25 avian species from 38 sites, ranged from –131 to –38. Regression analysis showed that strong correlations existed between both mean annual and growing-season D_p estimated by detrended interpolation and D_f of non-aquatic and non-corvid birds (r²=0.66 and 0.65, respectively). We also examined mean annual and growing-season ¹⁸O_p vs. ¹⁸O_f for our samples. Both oxygen regressions were similar (r²=0.56 and 0.57, respectively) but poorer than for deuterium. Our study reveals that D measurements of feathers from migratory birds in Europe may be used to track their origin and movements, and so provide a powerful investigative tool for avian migration research in Europe.     

15N natural abundance in forest and pasture soils of the Brazilian Amazon Basin

The natural abundance of ¹⁵N was examined in soil profiles from forests and pastures of the Brazilian Amazon Basin to compare tropical forests on a variety of soil types and to investigate changes in the sources of nitrogen to soils following deforestation for cattle ranching. Six sites in the state of Rondônia, two sites in Pará and one in Amazonas were studied. All sites except one were chronosequences and contained native forest and one or more pastures ranging from 2 to 27 years old. Forest soil ¹⁵N values to a depth of 1 m ranged from 8 to 23 and were higher than values typically found in temperate forests. A general pattern of increasing ¹⁵N values with depth near the soil surface was broadly similar to patterns in other forests but a decrease in ¹⁵N values in many forest profiles between 20 and 40 cm suggests that illuviation of ¹⁵N-depleted nitrate may influence total soil ¹⁵N values in deeper soil where total N concentrations are low. In four chronosequences in Rondônia, the ¹⁵N values of surface soil from pastures were lower than in the original forest and ¹⁵N values were increasingly depleted in older pastures. Inputs of atmospheric N by dinitrogen fixation could be an important N source in these pastures. Other pastures in Amazonas and Pará and Rondônia showed no consistent change from forest values. The extent of fractionation that leads to ¹⁵N enrichment in soils was broadly similar over a wide range of soil textures and indicated that similar processes control N fractionation and loss under tropical forest over a broad geographic region. Forest ¹⁵N profiles were consistent with conceptual models that explain enrichment of soil ¹⁵N values by selective loss of ¹⁴N during nitrification and denitrification.     

Sulfur isotope inventories of atmospheric deposition, spruce forest floor and living Sphagnum along a NW–SE transect across Europe

At five European sites, differing in atmospheric Sinputs by a factor of 6, and differing in S isotope signatures ofthese inputs by up to 14 (CDT), we investigated thedirection and magnitude of an assimilation-related ³⁴S shiftand the relationship between atmospheric deposition and Sretention in selected ecosystem compartments. Bulk precipitationand spruce throughfall were collected between 1994 and 1996 inthe Isle of Mull (Scotland), Connemara (Ireland), Thorne Moors(England), Rybárenská slat' and Oceán (both Czech Republic) andanalyzed for sulfate concentrations and ³⁴S ratios. Eighteenreplicate samples per site of living Sphagnum collected inunforested peatlands and 18 samples of spruce forest floorcollected near each of the peatlands were also analyzed for Sconcentrations and ³⁴S ratios. Assimilation of S was associatedwith a negative ³⁴S shift. Plant tissues systematicallypreferred the light isotope ³²S, on average by 2. There wasa strong positive correlation between the non-marine portion ofthe atmospheric S input and total S concentration in forest floorand Sphagnum, respectively (R = 0.97 and R = 0.85). Elevated Sinputs lead to higher S retention in these two organic-richcompartments of the ecosystem. It follows that equal emphasismust be placed on organic S as on adsorption/desorption ofinorganic sulfate when studying acidification reversal inecosystems. The sea-shore sites had rainfall enriched in theheavy isotope ³⁴S due to an admixture of sea-spray. The inlandsites had low ³⁴S reflecting ³⁴S of sulfur emitted from localcoal-burning power stations. Sphagnum had always lower S contentsand higher ³⁴S ratios compared to forest floor. The within-siterange of ³⁴S ratios of Sphagnum and forest floor was wide (upto 12) suggesting that at least six replicate samples shouldbe taken when using ³⁴S as a tracer.