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51.
GIOVANNA BATTIPAGLIA PAOLO CHERUBINI† MATTHIAS SAURER‡ ROLF T. W. SIEGWOLF‡ SANDRO STRUMIA M. FRANCESCA COTRUFO 《Global Change Biology》2007,13(6):1122-1137
Volcanic eruptions impact the global and the hemispheric climate, but it is still unknown how and to what degree they force the climate system and in particular the global carbon cycle. In this paper, the relationships between individual eruptions (reconstructed for the past using written records), tree primary productivity (estimated using ring widths), photosynthetic rate and stomatal conductance (assessed by carbon and oxygen isotope data) are investigated, to understand the impact of volcanic eruptions on net primary production. Data from a mixed stand of Fagus sylvatica L. and Acer pseudoplatanus L. located in the area of the Vesuvio volcanic complex (Southern Italy) showed a significant decrease in ring width following each eruption. Isotope analyses indicate a change in climatic conditions after such events. Specifically, the lower oxygen isotope ratio in the tree‐ring cellulose strongly suggests an increase in relative humidity and a decrease in temperature, with the latter resulting in a strong limitation to tree‐ring growth. The carbon isotope ratio was only moderately but not significantly reduced in the years of volcanic eruption, suggesting no major changes in C fixation rates. This work is a case study on the effects of volcanic eruptions resulting in strong climatic changes on the local scale. This is an opportunity to explore the process and causal relationships between climatic changes and the response of the vegetation. Thus, we propose here a realistic model scenario, from which we can extrapolate to global scales and improve our interpretations of results of global studies. 相似文献
52.
J. Custot Jean-Luc Boucher Sandrine Vadon Catherine Guedes Sylvie Dijols Marcel Delaforge Daniel Mansuy 《Journal of biological inorganic chemistry》1996,1(1):73-82
The effects of various compounds bearing an N-OH group such as N-hydroxy-guanidines, amidoximes, and hydroxylamines, on bovine and rat liver arginases was studied. Some of these compounds
with an l-α-amino acid function at an appropriate distance from the N-OH group acted as strong competitive liver arginase inhibitors,
displaying Ki values between 4 and 150 μM. Two compounds, N
ε-hydroxy-l-lysine and N
ω-hydroxy-d,l-indospicine, which exhibited Ki values of 4 and 20 μM (at pH 7.4), were the most potent inhibitors of arginase described
to date. The distance between the α-amino acid and N-OH functions appeared to be crucial for potent inhibition of arginase,
as N
948;-hydroxy-l-ornithine, which has one -CH2 group less than N
ε-hydroxy-l-lysine, exhibited a 37-fold higher Ki value than N
ε-hydroxy-l-lysine. Based on these results, a model for the interaction of N
ω-hydroxyamino-l-α-amino acids with the arginase active site is proposed. This model involves the binding of the N-OH group of the inhibitors
to the arginase Mn(II) center and suggests that N
ε-hydroxy-l-lysine is a good transition state analog of arginase. 相似文献
53.
54.
Pain DJ Green RE Giebetaing B Kozulin A Poluda A Ottosson U Flade M Hilton GM 《Oecologia》2004,138(2):168-174
Understanding the links between breeding and wintering areas of migratory species has important ecological and conservation implications. Recently, stable isotope technology has been used to further our understanding. Stable isotope ratios vary geographically with a range of biogeochemical factors and isotope profiles in organisms reflect those in their food and environment. For inert tissues like feathers, isotope profiles reflect the environment in which they were formed. Following large-scale habitat destruction, the globally threatened aquatic warbler Acrocephalus paludicola has a fragmented breeding population across central Europe, largely in Belarus, Poland and Ukraine. The species sub-Saharan African wintering grounds have not yet been discovered, and this significantly hampers conservation efforts. Aquatic warblers grow their flight feathers on their wintering grounds, and we analysed stable isotope ratios (948.gif" alt="delta" align="BASELINE" BORDER="0">15N, 948.gif" alt="delta" align="BASELINE" BORDER="0">13C, 948.gif" alt="delta" align="BASELINE" BORDER="0">D) in rectrices of adults from six main breeding sites (subpopulations) across Europe to determine whether different breeding subpopulations formed a single mixed population on the wintering grounds. 948.gif" alt="delta" align="BASELINE" BORDER="0">15N varies considerably with dietary trophic level and environmental factors, and 948.gif" alt="delta" align="BASELINE" BORDER="0">D with the 948.gif" alt="delta" align="BASELINE" BORDER="0">D in rainfall; neither varied between aquatic warbler subpopulations. Uniform feather 948.gif" alt="delta" align="BASELINE" BORDER="0">15N signatures suggest no major variation in dietary trophic level during feather formation. High variance and inter-annual differences in mean 948.gif" alt="delta" align="BASELINE" BORDER="0">D values hinder interpretation of these data. Significant differences in mean 948.gif" alt="delta" align="BASELINE" BORDER="0">13C ratios existed between subpopulations. We discuss possible interpretations of this result, and consider differences in moulting latitude of different subpopulations to be the most parsimonious. 948.gif" alt="delta" align="BASELINE" BORDER="0">13C in plants and animals decreases with latitude, along a steep gradient in sub-Saharan Africa. Birds from the most north-westerly breeding subpopulation (Karsibor, Poland) had significantly lower variance in 948.gif" alt="delta" align="BASELINE" BORDER="0">13C and 948.gif" alt="delta" align="BASELINE" BORDER="0">15N than birds from all other sites, suggesting either that birds from Karsibor are less geographically dispersed during moult, or moult in an area with less isotopic heterogeneity. Mean 948.gif" alt="delta" align="BASELINE" BORDER="0">13C signatures from winter-grown feathers of different subpopulations were positively correlated with the latitude and longitude of breeding sites, suggesting a strong relationship between European breeding and African winter moulting latitudes. The use of stable isotopes provides novel insights into migratory connectivity and migration patterns in this little-known threatened species. 相似文献
55.
In this study we show that the natural abundance of the nitrogen isotope 15, 948;15N, of plants in heath tundra and at the tundra-forest ecocline is closely correlated with the presence and type of mycorrhizal
association in the plant roots. A total of 56 vascular plant species, 7 moss species, 2 lichens and 6 species of fungi from
four heath and forest tundra sites in Greenland, Siberia and Sweden were analysed for 948;15N and N concentration. Roots of vascular plants were examined for mycorrhizal colonization, and the soil organic matter was
analysed for 948;15N, N concentration and soil inorganic, dissolved organic and microbial N. No arbuscular mycorrhizal (AM) colonizations were
found although potential host plants were present in all sites. The dominant species were either ectomycorrhizal (ECM) or
ericoid mycorrhizal (ERI). The 948;15N of ECM or ERI plants was 3.5–7.7‰ lower than that of non-mycorrhizal (NON) species in three of the four sites. This corresponds
to the results in our earlier study of mycorrhiza and plant 948;15N which was limited to one heath and one fellfield in N Sweden. Hence, our data suggest that the 948;15N pattern: NON/AM plants > ECM plants ≥ ERI plants is a general phenomenon in ecosystems with nutrient-deficient organogenic
soils. In the fourth site, a␣birch forest with a lush herb/shrub understorey, the differences between functional groups were
considerably smaller, and only the ERI species differed (by 1.1‰) from the NON species. Plants of all functional groups from
this site had nearly twice the leaf N concentration as that found in the same species at the other three sites. It is likely
that low inorganic N availability is a prerequisite for strong 948;15N separation among functional groups. Both ECM roots and fruitbodies were 15N enriched compared to leaves which suggests that the difference in 948;15N between plants with different kinds of mycorrhiza could be due to isotopic fractionation at the␣fungal-plant interface.
However, differences in 948;15N between soil N forms absorbed by the plants could also contribute to the wide differences in plant 948;15N found in most heath and forest tundra ecosystems. We hypothesize that during microbial immobilization of soil ammonium the
microbial N pool could become 15N-depleted and the remaining, plant-available soil ammonium 15N-enriched. The latter could be a main source of N for NON/AM plants which usually have high 948;15N. In contrast, amino acids and other soil organic N compounds presumably are 15N-depleted, similar to plant litter, and ECM and ERI plants with high uptake of these N forms hence have low leaf 948;15N. Further indications come from the 948;15N of mosses and lichens which was similar to that of ECM plants. Tundra cryptogams (and ECM and ERI plants) have previously
been shown to have higher uptake of amino acid than ammonium N; their low 948;15N might therefore reflect the 948;15N of free amino acids in the soil. The concentration of dissolved organic N was 3–16 times higher than that of inorganic N
in the sites. Organic nitrogen could be an important N source for ECM and, in particular, ERI plants in heath and forest tundra
ecosystems with low release rate of inorganic N from the soil organic matter.
Received: 8 June 1997 / Accepted: 28 February 1998 相似文献
56.
The chemical and biological characteristics of humus within the Ah horizon (Calcic-Luvisol) have been studied. Attention was paid to variation in the NMR spectra of humic fractions and 948.gif" alt="delta" align="BASELINE" BORDER="0"> 13C values and to how these changes are related to different biological humic fraction activities.The chemical changes in particular involve the decrease of the aromatic component and the increase of the non-aromatic component within the horizon and the different 948.gif" alt="delta" align="BASELINE" BORDER="0"> 13C value not only within the horizon but also among the humic fractions distinctive of different molecular sizes.An attempt has been made to explain the vertical chemical changes in terms of processes affecting the biological characteristics of the high and low molecular size humic fractions. The main conclusions are that the low molecular size humic fractions, in the upper part of the horizon, are of greater importance with respect to the other humic fractions in influencing the enzyme activities linked to growth metabolism. The biological role of the high molecular size humic fractions characterised by a relevant content of peptidic- and carbohydratic-C is also presented. 相似文献
57.
The effects of , 948.gif" alt="delta" align="BASELINE" BORDER="0">, and receptor-agonists on forskolin stimulated cyclic adenosine-3, 5-monophosphate (cAMP) formation were examined in astroglial enriched primary cultures from the cerebral cortex of newborn rats. Intracellular cAMP accumulation was quantified by radioimmunoassay. Morphine was used as a -receptor agonist, D-Ala-D-Leu-Enkephalin (DADLE) as a 948.gif" alt="delta" align="BASELINE" BORDER="0">-receptor agonist and dynorphine 1–13 (Dyn) as a -receptor agonist. Basal cAMP levels were unaffected by either the opiate agonists or the antagonists used. In the presence of the cAMP stimulator forskolin, morphine had no significant effect on the cytoplasmic cAMP levels. DADLE caused a dose related inhibition of the forskolin stimulated cAMP accumulation. The effects of this 948.gif" alt="delta" align="BASELINE" BORDER="0"> receptor stimulation was blocked with the selective antagonist ICI 174.864. In the presence of Dyn, the forskolin stimulated cAMP accumulation was inhibited in a dose related manner. This receptor stimulation was blocked with the selective antagonist MR 2266. Co-administration of DADLE and Dyn resulted in a non additive inhibition of the forskolin stimulated accumulation of cAMP. These findings indicate that astroglial enriched cultures from the cerebral cortex of rats express 948.gif" alt="delta" align="BASELINE" BORDER="0"> and -receptors co-localized ont he same population of cells, and that these receptors are inhibitory coupled to adenylate cyclase. 相似文献
58.
To better understand the relationship between salinity and the carbon stable isotope composition (expressed as 948;13C) of mangrove plants and to test whether the patterns of variation in 948;13C of mangrove plants differ from those of nonhalophytes as response to salinity, the effect of salinity on leaf 948;13C in two dominant mangrove species, Aegiceras corniculatum and Kandelia candel, was studied. Furthermore, to determine whether the variation in 948;13C of mangrove species is adjusted by stomatal conductance, K. candel was selected as an example, and leaf gas-exchange characteristics of the seedlings were measured. It was observed that both
mangrove species had a lower leaf 948;13C under their optimum salinity (1.50% for Ae. corniculatum and 2.00% for K. candel). This variation in 948;13C of mangrove plants was attributable largely to stomatal adjustment as for nonhalophytes in which a strong correlation between
948;13C and relevant photosynthetic properties is observed. This result suggests that the different response pattern in 948;13C was a consequence of the variation in stomata in relation to the different tolerance to salinity. The optimum salinity inferred
by leaf 948;13C provides a feasible method for comparing salt tolerance between mangrove plants belonging to different species, which is
useful for mangrove restoration. 相似文献
59.
Sudha Rao Gopalakrishna Kamath Gururaj Maralihalli Anil S. Bhagwat 《Photosynthesis research》1987,12(2):155-164
The 948.gif" alt="delta" align="BASELINE" BORDER="0">-aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of 948.gif" alt="delta" align="BASELINE" BORDER="0">-ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations 948.gif" alt="delta" align="BASELINE" BORDER="0">ALAD
948.gif" alt="delta" align="BASELINE" BORDER="0">-aminolevulinic acid dehydratase
- FMN
flavin mononucleotide
- O2
-
superoxide
- H2O2
hydrogen peroxide
- 102
singlet oxygen
- LA
levulinic acid
- PBG
porphobilinogen
- BSA
bovine serum albumin
- BME
2-mercaptoethanol
- SOD
superoxide dismutase
- pHMB
para-hydroxymercuribenzoate
- DTT
dithiothreitol
- FAD
flavin adenine dinucleotide
- NADH
nicotinamide adenine dinucleotide 相似文献
60.
The isotopic composition of tree ring cellulose was obtained over a 2-year period from small-diameter riparian-zone trees
at field sites that differed in source water isotopic composition and humidity. The sites were located in Utah (cool and low
humidity), Oregon (cool and high humidity), and Arizona (warm and low humidity) with source water isotope ratio values of
–125/–15‰ (948;D/948;18O), –48/–6‰, and –67/–7‰, respectively. Monthly environmental measurements included temperature and humidity along with measurements
of the isotope ratios in atmospheric water vapor, stream, stem, and leaf water. Small riparian trees used only stream water
(both 948;D and 948;18O of stem and stream water did not differ), but 948; values of both atmospheric water vapor and leaf water varied substantially
between months. Differences in ambient temperature and humidity conditions between sites contributed to substantial differences
in leaf water evaporative enrichment. These leaf water differences resulted in differences in the 948;D and 948;18O values of tree ring cellulose, indicating that humidity information was recorded in the annual rings of trees. These environmental
and isotopic measurements were used to test a mechanistic model of the factors contributing to 948;D and 948;18O values in tree ring cellulose. The model was tested in two parts: (a) a leaf water model using environmental information
to predict leaf water evaporative enrichment and (b) a model describing biochemical fractionation events and isotopic exchange
with medium water. The models adequately accounted for field observations of both leaf water and tree ring cellulose, indicating
that the model parameterization from controlled experiments was robust even under uncontrolled and variable field conditions.
Received: 7 April 1999 / Accepted: 8 December 1999 相似文献