Effect of<Emphasis Type="Italic"> p</Emphasis>CO<Subscript>2</Subscript> and temperature on the boron isotopic composition of the zooxanthellate coral<Emphasis Type="Italic"> Acropora</Emphasis> sp.

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     

Variation in stable isotope signatures of seston and a zooplanktivorous fish in a eutrophic Chinese lake

Temporal and spatial changes in ¹³C and ¹⁵N of seston (mainly phytoplankton) and isotopic relationship between seston and the lake anchovy (Coilia ectenes) were studied in the large eutrophic freshwater Lake Chaohu in China. Much of the spatial and temporal variation in ¹³C of lake anchovies was explained by variation in seston, indicating a strong link between pelagic primary production and higher order consumers. Because the lake is shallow, there were no significant differences in ¹³C and ¹⁵N of seston between surface and overlying waters. Spatially, the relatively high ¹³C and ¹⁵N of seston in the western part of the lake might be due to high levels of anthropogenically derived N and C introduced from the surrounding cities through sewage drainage systems. The trophic position of the lake anchovy in the food web of Lake Chaohu was estimated to be 2.9–4.1 (3.5 ± 0.4), which agrees well with the previous stomach content analysis suggesting that the lake anchovy fed both on zooplankton and small planktivorous fishes.     

Beaver alter stable carbon isotope ratios of benthic particulate organic matter

Beaver are well known to influence the geomorphology and geochemistry of boreal waters, in addition to being prominent vectors in the selective import of deciduous coarse woody debris (CWD). Because the stable carbon isotope ratios of deciduous trees are lower than those of coniferous trees, the possibility exists that the ¹³C values of particulate organic matter near beaver lodges may differ from those characteristic for littoral regions without beaver activity. In agreement with this supposition, ¹³C was found to significantly increase in progressively smaller size fractions of CWD collected from near lodges, probably due to the more rapid breakdown, decomposition and disappearance of deciduous material.     

Nitrogen isotope ratios shift with plant size in tropical bromeliads

We describe an ontogenetic shift in nitrogen (N) isotopic values in two rosette-forming epiphytic bromeliads. Leaf tissue N isotope values of small individuals of two bromeliad species (mean –6.2) differed from those of large individuals within each species (mean –0.5). Using references for potential N sources, we calculated the relative contribution of autochthonous (soil-derived through leaf litter) and allochthonous (atmospheric deposition) N with a two-member mixing model. Atmospheric sources contributed as much as 77–80% of the N in small individuals, whereas soil-derived N contributed 64–72% (conservative reference value) to 100% (less conservative reference value) of leaf tissue N in large plants. Shifts in N source with increasing plant size may be important aspects of rainforest complexity, an understudied aspect of ecosystem diversity.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Sources of organic and inorganic carbon in a headwater stream: Evidence from carbon isotope studies

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).     

Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria

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.     

Wood ash treatment affects seasonal N fluctuations in needles of adult<Emphasis Type="Italic"> Picea abies</Emphasis> trees: a <Superscript>15</Superscript>N-tracer study

A ¹⁵N-tracer experiment was carried out in a stand of adult spruce trees [Picea abies (L.) Karst.] located on the Swiss Plateau in order to investigate the effects of wood ash treatment on seasonal nitrogen fluctuations in fine roots and needles. Treatments included irrigation (W), liquid fertilization (LF) and wood ash (A) application. ¹⁵N fluctuation in fine roots and current to 3-year-old needles was studied after one ¹⁵N pulse for 2 consecutive years (1999, 2000). ¹⁵N tracer was rapidly incorporated into the fine roots of adult trees, and ¹⁵N values reached similar levels in all treatments 2 months after the pulse. In the needles, the largest increase in ¹⁵N was observed in those of the current year. Following the initial peak during spring growth, ¹⁵N values in needles of control trees showed an oscillating pattern through the season. This oscillation is attributed to the increased use of internal N sources, as soon as the roots can no longer meet the increased N demand during the sprouting phase. However, W-, LF- and A-treated trees no longer showed the oscillation in ¹⁵N. Additional water (W and LF) as well as fertilizer (A and LF) may have induced shifts in the microbial flora, thus increasing the unlabelled N release from the soil. The strongest dampening was observed for the A treatment, indicating sufficient N availability from the soil, and making intensive use of the internal N sources unnecessary. Treatment with wood ash thus resulted in a similar fertilizer response to liquid fertilization.     

Stable carbon isotope analysis of soil organic matter illustrates vegetation change at the grassland/woodland boundary in southeastern Arizona,USA

In southeastern Arizona, Prosopis juliflora (Swartz) DC. and Quercus emoryi Torr. are the dominant woody species at grassland/woodland boundaries. The stability of the grassland/woodland boundary in this region has been questioned, although there is no direct evidence to confirm that woodland is encroaching into grassland or vice versa. We used stable carbon isotope analysis of soil organic matter to investigate the direction and magnitude of vegetation change along this ecotone. ¹³C values of soil organic matter and roots along the ecotone indicated that both dominant woody species (C₃) are recent components of former grasslands (C₄), consistent with other reports of recent increases in woody plant abundance in grasslands and savannas throughout the world. Data on root biomass and soil organic matter suggest that this increase in woody plant abundance in grasslands and savannas may increase carbon storage in these ecosystems, with implications for the global carbon cycle.     

Stable carbon isotope ratio variations in marine macrophytes along intertidal gradients

Summary The hypothesis that relative water motion and boundary layer diffusion processes affect carbon isotope ratios of aquatic plants was tested in tidal pool and surge zone comparisons of the surfgrass Phyllospadix spp. No evidence was found that submerged plants growing in still upper tidal pools were isotopically different from those growing submerged in lower tidal surge zones. Significant decreases in ¹³C/¹²C ratios for plants growing emersed in the intertidal may have been caused by uptake of atmospheric carbon dioxide. Marine algae (Egregia menziesii and Halosaccion americanum) growing at the same location and tidal elevations as the seagrasses showed somewhat different isotopic fractionation patterns, suggesting that causes of isotopic variability in the seagrasses were not necessarily the same as those in the two marine algae.     

Development of a hybrid <Emphasis Type="Italic">delta</Emphasis>-endotoxin and its expression in tobacco and cotton for control of a polyphagous pest <Emphasis Type="Italic">Spodoptera litura</Emphasis>

A hybrid -endotoxin protein was designed against a polyphagous lepidopteran insect pest Spodoptera litura, which is tolerant to most of the known -endotoxins. The hybrid -endotoxin was created by replacing amino acid residues 530–587 in a poorly active natural Cry1Ea protein, with a highly homologous 70 amino acid region of Cry1Ca in domain III. The truncated -endotoxins Cry1Ea, Cry1Ca and the hybrid protein Cry1EC accumulated in Escherichia coli to form inclusion bodies. The solubilised Cry1EC made from E. coli was 4- fold more toxic to the larvae of S. litura than Cry1Ca, the best known -endotoxin against Spodoptera sp. None of the two truncated toxins, solubilised from E. coli caused larval mortality. However, trypsinised Cry1Ca protoxin obtained from E. coli and solubilised from inclusion bodies caused mortality of S. litura with LC₅₀ 513 ng/ml semi synthetic diet. A synthetic gene coding for the hybrid$-endotoxin Cry1EC was designed for high level expression in plants, taking into consideration several features found in the highly expressed plant genes. Transgenic, single copy plants of tobacco as well as cotton were developed. The selected lines expressed Cry1EC at 0.1–0.7% of soluble leaf protein. Such plants were completely resistant to S. litura and caused 100% mortality in all stages of larval development. Hence, unlike in E. coli, the hybrid -endotoxin folded into a functionally active conformation in both tobacco and cotton leaves. The truncated Cry1EC expressed in tobacco leaves was about 8-fold more toxic (LC₅₀ 58 ng/ml diet) compared to expression in E. coli.     

A novel family of mitochondrial proteins is represented by the <Emphasis Type="Italic">Drosophila</Emphasis> genes <Emphasis Type="Italic">slmo</Emphasis>, <Emphasis Type="Italic">preli-like</Emphasis> and <Emphasis Type="Italic">real-time</Emphasis>

Mitochondria play essential roles in development and disease. The characterisation of mitochondrial proteins is therefore of particular importance. The slowmo (slmo) gene of Drosophila melanogaster has been shown to encode a novel type of mitochondrial protein, and is essential in the developing central nervous system. The Slmo protein contains a conserved PRELI/MSF1p domain, found in proteins from a wide variety of eukaryotic organisms. However, the function of the proteins of this family is currently unknown. In this study, the evolutionary relationships between members of the PRELI/MSF1p family are described, and we present the first analysis of two novel Drosophila genes predicted to encode proteins of this type. The first of these, preli-like (prel), is expressed ubiquitously during embryonic development, whilst the second, real-time (retm), is expressed dynamically in the developing gut and central nervous system. retm encodes a member of a novel conserved subclass of larger PRELI/MSF1p domain proteins, which also contain the CRAL-TRIO motif thought to mediate the transport of small hydrophobic ligands. Here we provide evidence that, like Slmo, both the Prel and Retm proteins are localised to the mitochondria, indicating that the function of the PRELI/MSF1p domain is specific to this organelle.Edited by P. Simpson     

Carbon and nitrogen dynamics along the decay continuum: Plant litter to soil organic matter

Decay processes in an ecosystem can be thought of as a continuum beginning with the input of plant litter and leading to the formation of soil organic matter. As an example of this continuum, we review a 77-month study of the decay of red pine (Pinus resinosa Ait.) needle litter. We tracked the changes in C chemistry and the N pool in red pine (Pinus resinosa Ait.) needle litter during the 77-month period using standard chemical techniques and stable isotope, analyses of C and N.Mass loss is best described by a two-phase model: an initial phase of constant mass loss and a phase of very slow loss dominated by degradation of lignocellulose (acid soluble sugars plus acid insoluble C compounds). As the decaying litter enters the second phase, the ratio of lignin to lignin and cellulose (the lignocellulose index, LCI) approaches 0.7. Thereafter, the LCI increases only slightly throughout the decay continuum indicating that acid insoluble materials (lignin) dominate decay in the latter part of the continuum.Nitrogen dynamics are also best described by a two-phase model: a phase of N net immobilization followed by a phase of N net mineralization. Small changes in C and N isotopic composition were observed during litter decay. Larger changes were observed with depth in the soil profile.An understanding of factors that control lignin degradation is key to predicting the patterns of mass loss and N dynamics late in decay. The hypothesis that labile C is needed for lignin degradation must be evaluated and the sources of this C must be identified. Also, the hypothesis that the availability of inorganic N slows lignin decay must be evaluated in soil systems.     

Interpretation of sulfur cycling in two catchments in the Black Forest (Germany) using stable sulfur and oxygen isotope data

The isotopic composition of SO ₄ ^2- in bulk precipitation, canopy throughfall, seepage water at three different soil depths, stream water, and groundwater was monitored in two forested catchments in the Black Forest (Germany) between November 1989 and February 1992. Isotope measurements on aqueous sulfate were complemented by ³⁴S-analyses on SO₂ in the air, total sulfur and inorganic sulfate in the soil, and bedrock sulfur, in order to identify sources and biogeochemical processes affecting S cycling in catchments with base poor, siliceous bedrock. Stable S isotope data indicated that atmospheric deposition and not mineral weathering is the major source of S in both catchments since ³⁴S-values for sulfate in the soil, in seepage water, and in stream water were generally found to be similar to the mean ³⁴S-values of precipitation SO ₄ ^2- (+2.1. However, ¹⁸O-values of seepage water SO ₄ ^2- at 30 cm and especially at 80 cm depth were depleted by several per mil with respect to those of the atmospheric deposition (+7.5 to +13.5. This indicates that in both catchments a considerable proportion of the seepage water SO ₄ ^2- is derived from mineralization of carbon-bonded soil S and must therefore have cycled through the organic soil S pool. ³⁴S-values for different S compounds in the solid soil were found to differ markedly depending on S fraction and soil depth. Since atmospheric S deposition with rather constant ³⁴S-values was identified as the dominant S source in both catchments, this is interpreted as a result ofin situ isotope fractionation rather than admixture of isotopically different S. The differences between the ³⁴S-values of seepage water and soil sulfate and those of organic soil S compounds are consistent with a model in which SO ₄ ^2- uptake by vegetation and soil microorganisms favours³⁴SO ₄ ^2- slightly, whereas during mineralization of organic soil S to aqueous SOSO ₄ ^2- ,³²S reacts preferentially. However, the data provide evidence for negligible isotope fractionation during physico-chemical S transformations such as adsorption/desorption in aerated forest soils.     

A global survey of carbon isotope discrimination in plants from high altitude

Summary Carbon 13/12 isotope ratios have been determined from leaves of a hundred C₃ plant species (or ecotypes) from all major mountain ranges of the globe, avoiding drought stressed areas. A general increase in ¹³C content was found with increasing altitude, i.e. overall discrimination against the heavy isotope is reduced at high elevation. The steepest decline of discrimination is observed in taxa typically ranging to highest elevations (e.g. the genus Ranunculus). Mean ¹³C for all samples collected between 2500 and 5600 m altitude is-26.15 compared to the lowland average of-28.80 (P<0.001). Forbs from highest elevations reach-24. According to theory of ¹³C discrimination this indicates decreasing relative limitation of carbon uptake by carboxylation. In other words, we estimate that the ratio of internal to external partial pressure of CO₂ (p _i /p _a )in leaves of high elevation plants is lower than in leaves of low altitude. These results confirm recent gas exchange analyses in high and low elevation plants.     

Significance of rooting depth in mire plants: Evidence from natural <Superscript>15</Superscript>N abundance

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.     

A rapid and simple method for staining of the crystal protein ofBacillus thuringiensis

Summary A rapid and simple method of staining for the crystal protein (-endotoxin or parasporal body) ofBacillus thuringiensis has been developed. Changes in colonial morphology were observed when cells lost their ability to form crystal protein or both crystal protein and spore.     

Deuterium stable isotope ratios as tracers of water resource use: an experimental test with rock doves

Naturally-occurring deuterium stable isotope ratios can potentially be used to trace water resource use by animals, but estimating the contribution of isotopically distinct water sources requires the accurate prediction of isotopic discrimination factors between water inputs and an animals body water pool. We examined the feasibility of using estimates of water fluxes between a bird and its environment with a mass-balance model for the deuterium stable isotope ratio of avian body water (D_body) to predict isotopic discrimination factors. Apparent fractionation and thus discrimination factors were predicted to vary with the proportion of an animals total water losses than could be attributed to evaporative processes. To test our ability to predict isotopic discrimination, we manipulated water intake and evaporative water loss in rock doves (Columba livia) by providing them with fresh water or 0.15 M NaCl solution in thermoneutral or hot environments. After we switched the birds from drinking water with D=–95 VSMOW (Vienna Standard Mean Ocean Water) to enriched drinking water with D=+52 VSMOW, steady-state D_body was approached asymptotically. The equilibrium D_body was enriched by 10–50 relative to water inputs. After isotopic equilibrium was reached, the degree of enrichment was positively related (r²=0.34) to the fraction of total water loss that occurred by evaporation supporting the major prediction of the model. The variation we observed in discrimination factors suggests that the apparent fractionation of deuterium will be difficult to predict accurately under natural conditions. Our results show that accurate estimates of the contribution of different water sources to a birds body water pool require large deuterium isotopic differences between the sources.     

GPR80/99, proposed to be the P2Y<Subscript>15</Subscript> receptor activated by adenosine and AMP,is not a P2Y receptor

The orphan receptor GPR80 (also called GPR99) was recently reported to be the P2Y₁₅ receptor activated by AMP and adenosine and coupled to increases in cyclic AMP accumulation and intracellular Ca²⁺ mobilization (Inbe et al. J Biol Chem 2004; 279: 19790–9). However, the cell line (HEK293) used to carry out those studies endogenously expresses A_2A and A_2B adenosine receptors as well as multiple P2Y receptors, which complicates the analysis of a potential P2Y receptor. To determine unambiguously whether GPR80 is a P2Y receptor subtype, HA-tagged GPR80 was either stably expressed in CHO cells or transiently expressed in COS-7 and HEK293 cells, and cell surface expression was verified by radioimmunoassay (RIA). COS-7 cells overexpressing GPR80 showed a consistent twofold increase in basal inositol phosphate accumulation. However, neither adenosine nor AMP was capable of promoting accumulation of either cyclic AMP or inositol phosphates in any of the three GPR80-expressing cells. A recent paper (He et al. Nature 2004; 429: 188–93) reported that GPR80 is a Gq-coupled receptor activated by the citric acid cycle intermediate, -ketoglutarate. Consistent with this report, -ketoglutarate promoted inositol phosphate accumulation in CHO and HEK293 cells expressing GPR80, and pretreatment of GPR80-expressing COS-7 cells with glutamate dehydrogenase, which converts -ketoglutarate to glutamate, decreased basal levels of inositol phosphates. Taken together, these data demonstrate that GPR80 is not activated by adenosine, AMP or other nucleotides, but instead is activated by -ketoglutarate. Therefore, GPR80 is not a new member of the P2Y receptor family.     

Changes in soil organic matter with cropping as measured by organic carbon fractions and 13C natural isotope abundance

The decline in soil organic matter with cropping is a major factor affecting the sustainability of cropping systems. Changes in total C levels are relativelyinsensitive as a sustainability measure. Oxidation with different strength KMnO₄ has been shown to be a more sensitive indicator of change. The relative size of soil C fractions oxidised by 333 mM KMnO₄ declined with cropping, whilst the relative size of the unoxidised fraction increased. Changes in ¹³C ratio have been used to measure C turnover in systems which include C3 and C4 species.     

Emission of gaseous nitrogen oxides from an extensively managed grassland in NE Bavaria, Germany.

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 g_dw ^–1) and still produced N₂O from denitrification. Under denitrifying incubation conditions, much more N₂O was formed (0.91 mol g_dw ^–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.