The forest floor needle mass and the decomposition rates of pine needle litter in a European climate transect were studied in order to estimate the impact of climate change on forest soil carbon sequestration. Eight pine forests preserved from fire were selected along a climatic latitudinal gradient from 40° to 60° N, from Spain and Portugal to Sweden. The forest floor (Oi and Oe layers) was sorted into five categories of increasing decomposition level according to morphological criteria. The needle mass loss in each category was determined using a linear mass density method. The needle decomposition rate was calculated from the needle fall (NF), the mass of each category and its mass loss. For each site, the remaining mass vs. the calculated time was best fitted by an asymptotic model which indicates that the organic matter should be made up of two fractions: a decomposable one and a recalcitrant one. NF was correlated with actual evapotranspiration (AET) whereas the decomposition parameters (decomposition rate of the decomposable fraction, first year mass loss, forest floor needle mass, age of the most-decomposed category) were related to a combined response function to climate (CRF) based on the van’t Hoff law for temperature and the water deficit (DEF) for moisture. Scenarios with temperature increases, without and with DEF increases, were applied to predict forest floor needle mass changes. C would be lost from the forest floor if only temperature increases and this loss would increase from south to north. If more droughts occur, the forest floor would then tend to sequester C according to the level of the DEF and the latitude of the site. For example, a site in Portugal which is presently the most active site of the transect in terms of decomposition because of its present favourable warm Atlantic climate would react with a large range of responses, losing carbon under an unchanged precipitation regime and sequestering up to 3 times its present stock of carbon under drier conditions.

The litterbag method (LB) widely used in decomposition studies was compared to a direct observation method (DO) of the litter collected in the forest floor in three European Scots pine forests. In this last method, needles were sorted out of blocks of the forest floor and separated into 5 categories using morphological criteria representing different layers and decomposition levels. The residence time of the needles in each layer was calculated using the litterfall input, the size of the layer in the forest floor and its level of decomposition. The mass loss of each layer was determined using the linear mass density method. To estimate decomposition rates, the DO method might be more advantageous than the LB method because it is done without any manipulation or microclimatic artifact and because it integrates spatial and temporal variability. It is also convenient because the sampling does not have to be done simultaneously on different sites to allow site comparisons. Indeed, the collected litter blocks include the whole site history until the needle collapses which has been shown to take place after a period of up to 10 years in the present study. After 3 years, the mass loss was lower measured by the DO method than by the LB method. The decrease of litter mass measured by the DO method was best described by a simple asymptotic function of time. This model has a mechanistic signification because it underlines the possible long-term accumulation of recalcitrant products which is not the case with the exponential function. This accumulation of recalcitrant products is a key process in the storage of carbon in the organic matter reservoir of forest soils. Nevertheless this method is time consuming and cannot replace the LB method for large data set collection. This paper recommends when using the LB method to be aware of its inherent bias that can lead to misestimating decomposition in the long run.

SUMMARY Research interest in microbial biodiversity over the past 25 years has increased markedly as microbiologists have become interested in the significance of biodiversity for ecological processes and as the industrial, medical, and agricultural applications of this diversity have evolved. One major challenge for studies of microbial habitats is how to account for the diversity of extremely large and heterogeneous populations with samples that represent only a very small fraction of these populations. This review presents an analysis of the way in which the field of microbial biodiversity has exploited sampling, experimental design, and the process of hypothesis testing to meet this challenge. This review is based on a systematic analysis of 753 publications randomly sampled from the primary scientific literature from 1975 to 1999 concerning the microbial biodiversity of eight habitats related to water, soil, plants, and food. These publications illustrate a dominant and growing interest in questions concerning the effect of specific environmental factors on microbial biodiversity, the spatial and temporal heterogeneity of this biodiversity, and quantitative measures of population structure for most of the habitats covered here. Nevertheless, our analysis reveals that descriptions of sampling strategies or other information concerning the representativeness of the sample are often missing from publications, that there is very limited use of statistical tests of hypotheses, and that only a very few publications report the results of multiple independent tests of hypotheses. Examples are cited of different approaches and constraints to experimental design and hypothesis testing in studies of microbial biodiversity. To prompt a more rigorous approach to unambiguous evaluation of the impact of microbial biodiversity on ecological processes, we present guidelines for reporting information about experimental design, sampling strategies, and analyses of results in publications concerning microbial biodiversity.

The dynamics of plant decomposition in the soil were analysed in an altitudinal transect from 65 to 3968m under tropical conditions. Six sites were studied, with a mean annual temperature ranging from 5.5 to 27.4°C, and an annual precipitation from 790 to 1992mm. A 14C-labelled standard plant material was incubated in situ, at 5cm depth, over a period of 1.5–3years, depending on the altitude. The aim was to determine the contribution of climate (temperature and moisture) and of other factors, such as soil properties, to explaining the differences in mineralisation between the sites. Data analysis was performed using two-compartment models with first-order kinetics. To evaluate the effect of climate on decomposition, a response function to temperature (τ) and a response function to moisture (μ) were calculated. The kinetics of the remaining 14C were adjusted to the two-compartment first-order model considering successively time, τcum (cumulated τ), and τμcum (cumulated τμ) as independent variables. The assumption was that if the introduction of a climatic component into the explanatory variable reduces the distances between the decomposition curves of the sites, the differences are related to this factor. If the distance is not reduced, other factors in addition to climate must influence decomposition and/or the climatic response to altitude is not linear. The results show a clear decrease in decomposition with increasing altitude. Nevertheless, the altitudinal effect is not equal for the two fractions estimated using the two-compartment model. The size of the labile fraction decreased with altitude, whereas the recalcitrant fraction increased. The labile fraction decomposed very quickly, independently of the altitude, whereas the rate of decomposition of the recalcitrant fraction decreased with altitude. When τcum is used as the independent variable, the distance between the curves diminishes, indicating the great effect of temperature on decomposition, but in the high mountain sites, additional factors act. Using τμcum the difference between sites was not reduced, showing that the moisture effect is low or that the moisture response function is not appropriate.

Pseudomonas brassicacearum is a newly described bacterial species isolated from the rhizosphere of Arabidopsis thaliana. The P. brassicacearum populations were isolated from the rhizosphere of two ecotypes of A. thaliana (Wassilewskija (WS) and Columbia (COL)), a mutant of Columbia impaired in starch metabolism (pgm mutant), and a genetically distant plant (wheat), grown in a French eutric cambisol (Méréville). The strains were isolated on semi-selective media. Their diversity was assessed using repetitive extragenic palindromic (REP)-PCR profiling and their affiliation to the P. brassicacearum species using ARDRA and siderotyping. A total of 379 strains isolated in two experiments were clustered into 68 REP-genotypes. Statistical analysis showed that the genetic structure of the P. brassicacearum populations was homogeneous for strains isolated from different plants of the same genotype within the same experiment, but significantly differed across the four tested plant genotypes. Comparison of the REP-genotype distributions showed that some bacterial genotypes were poorly represented, whereas others were strongly stimulated by plant roots.

Pinus pinaster (Soland) litter was sampled from a Mediterranean forest floor in order to study decomposition kinetics under natural conditions. Needles were divided into five distinct and successive compartments L, F1a, F1b, F2a, F2b, according to their morphology. The methods of Kendrick (Kendrick, W.B., 1959. The time factor in the decomposition of Coniferous leaf litter. Canadian Journal of Botany 37, 907-912) and Gourbiere, (Gourbiere, F., 1981. Vie, senescence et decomposition des aiguilles de sapin (Abies alba Mill.) Part I: Methodologie et premiers resultats. Acta oecologica, Oecologica Plantarum 2, 223-232) were used to determine the mass loss of each compartment. On the forest floor, the total needle compartment represented 39% of the total decomposing litter mass and the five distinct compartments had similar mass values of 2.8-3.1 t ha(-1) ash-free material. The decomposition rate of each compartment was calculated from the mass compartment, its mass loss and the litter-fall in the site. The remaining mass in relation to calculated time was described by a single first-order decay model with a decomposition rate (k) of 0.135 year(-1) (R-2 = 0.86) or by an asymptotic model with k = 0.180 year(-1) and the asymptote at 83.2% (R-2 = 0.87). The first-year mass loss equalled 13%, and after 5.1 years it reached 50% for both models. (C) 2000 Elsevier Science Ltd. All rights reserved.

The genetic structure of Pseudomonas corrugata populations was investigated in bulk soil to evaluate the impact of crop management on the intraspecific diversity of this bacterium stimulated in plant rhizosphere. As these bacteria are rare in bulk soil, an immunotrapping assay was developed to isolate them from soils located in Grignon (France), where adjacent plots with similar soil features were cultivated under maize/wheat crop rotation or continuous wheat cropping. Genomic fingerprinting of 291 isolates was performed using repetitive sequence-based polymerase chain reaction (ERIC-PCR). Most of these isolates (236 out of 291) were assigned to P. corrugata on the basis of an amplified ribosomal DNA restriction analysis (ARDRA) with 12 restriction enzymes. Data were analyzed by Pearson's chi-squared tests and genetic diversity was evaluated with specific indices for richness and evenness. Comparison of richness or evenness diversity indices (global diversity) showed no significant difference, whereas ERIC-PCR fingerprinting data (intraspecific diversity) showed that the genetic structure of P. corrugata was significantly affected by crop management.

The diversity of Paenibacillus polymyxa populations associated with the rhizosphere of durum wheat was investigated in Algerian soils sampled in regions where wheat had been cultivated for 5 and 26 years (Hamiz, H5 and Z26), 70 years (Algiers, D70), and more than 2 000 years (Tiaret, T2000 and K2000). A total of 111 strains were isolated by immunotrapping and identified as P. polymyxa using an AP150CHB kit and restriction analysis of the amplified 16S rDNA gene. The phenotypic characteristics of the P. polymyxa populations were compared and the strains found not to cluster according to their origin. The longer the history of wheat cultivation, the lower the phenotypic diversity and the higher the frequency of nitrogen-fixing strains. Population genetic diversity, evaluated by ERIC-PCR, showed the same trends as phenotypic diversity. The distribution of ERIC genotypes among the different populations studied were compared using Pearson's Chi-squared test. The strains isolated in D70, 226, and H5 derived from soil populations sharing the same genetic structure, but those isolated in T2000 and K2000 each stemmed from a population with a specific genetic structure. These data suggest that the genetic structure of P. polymyxa populations has been affected by long-term wheat cultivation. (C) 2000 Editions scientifiques et medicales Elsevier SAS.

Spin-trapped radicals from gamma-irradiated dilinoleoyl-phosphatidyl choline, linoleic acid [C-18:2], glycerol and choline are compared. Three main radicals are detected in the phospholipid and in the fatty acid: D-1, D-2 and D-3; The glycerol and the choline signals are not recorded in the phospholipid. These results show that the fatty acid chains are the gamma rays target in the phospholipid molecule. D-1 and D-2, also detected in the autoxidized samples, are identified by analogy with ESR studies of C-18:2 autoxydation. The chemical structures assigned to spin-trapped radicals from C(18:2)are also available for radicals gamma-induced in C-18:1, C-18:3 and in the related phospholipids.

Les radicaux γ-induits dans le dilinoléoyl-phosphatidyl choline, l'acide linoléique [C18:2], le glycérol et la choline sont étudiés par la méthode de piégeage de spin. Trois radicaux principaux, D1, D2 et D3, sont détectés dans le phospholipide et dans l'acide gras. Les signaux du glycérol et de la choline ne sont pas retrouvés dans le phospholipide. Les chaînes des acides gras insaturés du phospholipide constituent donc la cible privilégiée des rayons γ. D1 et D2, enregistrés également dans les témoins auto-oxydes, sont identifiés par analogie avec des études par RPE de l'auto-oxydation de C18:2· Les structures chimiques proposées pour les radicaux piégés dans C18:2 sont étendues aux radicaux radioinduits dans C18:1, C18:3 et dans les phospholipides correspondants.

A field experiment was designed to follow the fate of fertilizer nitrogen in an annual crop (maize) and a permanent meadow (Digitaria decumbens) cultivated on an alfisol under the tropical two-season-climate of the Venezuelan Llanos.15N labelled urea equivalent to 150 kg N.ha−1 was added to field plots and to lysimeters of undisturbed soil.

As an approach to the conformational dynamics of erabutoxin b, the 1H2H exchange kinetics have been measured in 2H2O at 30°C, pH 4.75, by means of infrared spectrometry and high resolution 1H NMR. With a solvent exposure coefficient higher than 10−3 for 90 % of its backbone amide hydrogens, erabutoxin b shows a relatively large solvent accessibility: this is consistent with an open and/or flexible molecule. 17 backbone hydrogens and 9 side chain hydrogens exchange slowly. These results compare fairly well with the number of potential hydrogen bonds recently reported from X-ray analysis.

Temperature effects on the hydrogen exchange kinetics and the infrared spectra of two homologous snake neurotoxins (Laticauda semifasciata erabutoxin b and Naja nigricollis toxin α) were investigated between 10 and 40°C, at their isoionic pH. (1) Erabutoxin b is more accessible to the solvent than toxin α. (2) With increasing temperature, both toxin molecules undergo a global transition affecting the most accessible as well as the most buried hydrogens: the overall accessibility changes are more important for erabutoxin b than for toxin α. The different conformational stabilities of the toxins are also qualitatively supported by the temperature-induced shifts which affect the infrared amide I band of toxin α only. The existence of two conformer families could be responsible for the different conformational stability of these proteins.

1H2H exchange kinetics of the peptide hydrogens in corticotropin have been examined in 2H2O and CF3C2H2O2H solutions by means of infrared absorption measurements. In aqueous solution, around pH 3, the experimental data suggest a partially ordered structure, since in the two corticotropins 1–24 and 1–32 about 6 slowly exchanging peptide protons are numbered. These might belong to the N-terminal part of the molecule. The C-terminal 25–32 octapeptide segment appears to be unordered and slightly destabilizes the overall hormone conformation. For corticotropin1–24 in CF3C2H2O2H, the qualitative interpretation of infrared spectra and the quantitative analysis of exchange data give evidence of a strong stabilization: a predominantly α-helical structure is induced by trifluoroethanol.

The configuration and the conformation of alpha and beta anomers of pyrazomycin, cytidine and pseudouridine in aqueous solution have been investigated by 1H-NMR at 250 MHz. T1 proton relaxation measurements are an excellent method to determine the conformation of the base around the glycosidic linkage. Frequently, steric hindrance considerations can help to decide which conformations are possible in nucleoside anomer pairs. The proton-proton coupling constants indicate that the N conformer is largely predominant in the alpha anomers while the S conformer is particularly abundant in beta-pyrazomycin. The steric hindrance is much larger for alpha than for beta-nucleosides and change of a C-C to a C-N glycosidic bond reduces considerably the rotational possibilities of the base. The relaxation data show that alpha-cytidine adopts the anti conformation with gamma = 200 degrees in good agreement with the crystal structure and with the sterical computations. In the other case, when the syn and anti conformations are sterically accessible, the orientation of the base may be completely different from one nucleoside to the other. It can be predicted neither from the crystal structure nor from comparisons with similar compounds. For alpha-pseudo-uridine the predominant orientation of the base (gamma = 120 degrees) is in the boundary of the syn-anti regions; for beta-cytidine the syn (gamma = 65 degrees) and anti (gamma = 215 degrees) conformations are equiprobable at room temperature while beta-pseudouridine shows the syn conformation with gamma = 40 degrees, the smallest angle observed until now. There is no correlation between the N/S and syn-anti ratios.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConfiguration and conformation of the .alpha.- and .beta.-anomers of C-nucleosides by proton magnetic resonance spectroscopy: new criterion for determination of .alpha.- and .beta.-anomersTran Dinh Son, Jean Michel Neumann, Jean Marie Thiery, Huynh Dinh Tam, Jean Igolen, and Wilhelm GuschlbauerCite this: J. Am. Chem. Soc. 1977, 99, 10, 3267–3273Publication Date (Print):May 1, 1977Publication History Published online1 May 2002Published inissue 1 May 1977https://pubs.acs.org/doi/10.1021/ja00452a011https://doi.org/10.1021/ja00452a011research-articleACS PublicationsRequest reuse permissionsArticle Views297Altmetric-Citations31LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Chemischer InformationsdienstVolume 8, Issue 32 Physical Organic Chemistry ChemInform Abstract: CONFIGURATION AND CONFORMATION OF THE α- AND β-ANOMERS OF C-NUCLEOSIDES BY PROTON MAGNETIC RESONANCE SPECTROSCOPY- NEW CRITERION FOR DETERMINATION OF α- AND β-ANOMERS TRAN DINH SON TRAN DINH SON, TRAN DINH SON TRAN DINH SONSearch for more papers by this authorJ.-M. NEUMANN, J.-M. NEUMANNSearch for more papers by this authorJ.-M. THIERY, J.-M. THIERYSearch for more papers by this authorHUYNH DINH TAM HUYNH DINH TAM, HUYNH DINH TAM HUYNH DINH TAMSearch for more papers by this authorJ. IGOLEN, J. IGOLENSearch for more papers by this authorW. GUSCHLBAUER, W. GUSCHLBAUERSearch for more papers by this author TRAN DINH SON TRAN DINH SON, TRAN DINH SON TRAN DINH SONSearch for more papers by this authorJ.-M. NEUMANN, J.-M. NEUMANNSearch for more papers by this authorJ.-M. THIERY, J.-M. THIERYSearch for more papers by this authorHUYNH DINH TAM HUYNH DINH TAM, HUYNH DINH TAM HUYNH DINH TAMSearch for more papers by this authorJ. IGOLEN, J. IGOLENSearch for more papers by this authorW. GUSCHLBAUER, W. GUSCHLBAUERSearch for more papers by this author First published: August 9, 1977 https://doi.org/10.1002/chin.197732060Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue32August 9, 1977 RelatedInformation

Hydrogen-deuterium exchange kinetics of (Asn1-Val5) angiotensin II has been investigated by proton magnetic resonance at 250 MHz in deuterated trifluoroethanol, as an approach to the "in situ" hormone conformation. An interactive program was specially developed to perform the data analysis on a computer similar to those used for spectroscopic data acquisition. Nine exchange sites are evidenced and characterized by their individual kinetic parameters. Three of them are assigned to peptide NH hydrogens, and the six remaining to slowly exchanging side chain protons. At 11 degrees C, more than three peptide hydrogens, sterically hindered or involved in hydrogen bonds, do not exchange. These results corroborate previous circular dichroism and infrared investigations performed in the same solvent, and suggest a family of well-folded conformations, stabilized in trifluoroethanol by internal hydrogen bonds, involving both the backbone and the side chain hydrogens.

Hydrogen-deuterium exchange in 2H20 solutions of the two redox states of horse heart cytochrome c was investigated at 20 degrees C, pH 7, by mass spectrometry and infrared spectroscopy. Mass spectrometry indicates that ferricytochrome has 20 hydrogens unexchanged after 24 h, 28 hydrogens exchanging between 10 min and 24 h, and 156 hydrogens exchanging within 10 min; comparative values for ferrocytochrome are 45, 19 and 140. The displacement of the exchange curves obtained by infrared corresponds to 8 to 9 peptide hydrogens. These combined methods show many non-peptide hydrogens exchanging rapidly (87 and 79 for ferricytochrome c and ferrocytochrome c respectively), whereas others, probably buried inside the molecule and involved in hydrogen bonds, are not exchanged, even after 24 h (14 and 30 hydrogens respectively, which is relatively large for a small protein). Infrared results are given in terms of changes of standard free energy for the transconformational reaction which exposes the peptide hydrogens to solvent: in ferricytochrome c and ferrycoytochrome c, 30% and 40% respectively of the peptide hydrogens are protected by conformational transitions stabilized by more than 5 kcal/mol (21 kJ/mol), which implies a large increase in rigidity for the reduced form.