Biosynthèses microbiennes de sucres neutres sur un panel de différents sols et différents substrats

International audienceThe presence of neutral carbohydrates in soil organic matter (SOM) in significant amount is apparently in contradiction with their lability. It may result either from stabilization or from continuous recycling of SOM by micro-organisms and biosynthesis of microbial sugars. To address this question, it was necessary to precisely determine the average yield of sugar biosyntheses and the distribution of individual sugars. We performed incubations of 13C labelled substrates and quantified biosyntheses of neutral carbohydrates using compound-specific isotope ratio mass spectrometry. To investigate the natural variation of the microbial biotransformations, we varied the soil characteristics on the one hand and the substrate on the other. Incubation kinetics reflected the existence of two pools of carbohydrate metabolites. One pool was characterized by its lability with a mean residence time of about two weeks, whereas the second was preserved from biodegradation. The yield of sugar production by soil micro-organisms was poorly affected by the quality of the substrates glucose, cellulose and glycine, and very similar distributions of individual sugars were observed (Glc>Gal=Man=Rham>Xyl=Ara=Fuc). Soil type affected sugar biosyntheses slightly more, reflecting some diversity of either microbial communities or ecophysiology among soils. These results provided important indications to further calibrate a comprehensive model of carbohydrate dynamics in soils

Cases lysimètres de Cadarache : minéralisation et organisation de l'azote dans un agro-système de la Basse Vallée de la Durance. Impact d'une culture dérobée

Extrait de documentReview of work carried out at Cadarache using lysimeters methodology, particularly by means of nitrogen is labelling techniques : fate of nitrogenSynthèse des travaux réalisés à Cadarache à l'aide de la technique lysimétrique, notamment sur le devenir de l'azote après marquage à l'azote quinze

Transformations de l'azote et fuites ammoniacales à la suite de l'épandage par injection ou par surface de lisier de porc : essai en laboratoire utilisant du lisier marqué au 15N-ammoniacal

International audienceA laboratory experiment was designed to determine the fate of 15N-labelled slurry ammonium (15NH4-N) and compare soil inorganic-N distribution following surface applied or injected pig slurry. A system of cylindrical volatilisation chambers equipped to allow continuous trapping of ammonia (NH3) was used. Undisturbed soil columns were placed in the chambers prior to the application of slurry. A nitrogen balance including soil, air and plant analysis was established for both treatments, eight days after application. Average cumulative emissions of NH3 were 15% and 11% of the total ammoniacal-N added with the surface and injected treatments, respectively. After 8 days 55 % of the 15NH4-N applied through slurry injection was recovered in the soil inorganic-N pool: 37 % as 15NH4-N and 18 % as 15NO3-N. These figures compare with only 25% 15N-NH4 recovered with the surface applied slurry treatment: 7 % as 15NH4-N and 17 % as 15NO3-N. Immobilisation into soil organic-N accounted for 8 % of the 15NH4-N applied for the injected treatment and 6 % of the surface applied slurry-15N. 15N uptake by the grass was 2 % and 7 % for the injected and surface applied treatments, respectively. The percentage of added 15N accounted for was 76 % for the injected treatment and 53 % for the surface applied slurry treatment.Un essai en laboratoire a été effectué dans le but de déterminer le devenir de l'azote ammoniacal du lisier (marqué au 15N-NH4) et de comparer la distribution des formes minérales de l'azote selon la méthode d'apport du lisier, soit en surface, soit par injection. Un système de chambres de volatilisation équipées pour permettre le piégeage de l'ammoniac a été utilisé. Des colonnes de sol non remaniées sont placées dans les chambres avant l'apport de lisier. Un bilan azoté incluant le sol, l'air et les analyses de végétaux a été établi pour les 2 traitements, 8 jours après l'apport. Les émissions cumulées d'ammoniac s'établissent à 15% et 11% de l'N total ammoniacal apporté pour respectivement l'apport en surface et par injection. Après 8 jours, 55% de l'N ammoniacal marqué sont retrouvés dans le pool d'N inorganique du sol : 37% sous la forme ammoniacale et 18% sous forme de nitrates marqués. Ces résultats sont à comparer avec seulement 25% de l'N-NH4 retrouvés dans le sol pour le traitement avec apport de lisier en surface : 7% sous forme ammoniacale et 17% sous forme nitrique. L'immobilisation dans le sol sous forme N-organique représente 8% de l'15N-NH4 apporté par le traitement injecté et 6% pour l'apport en surface. Le prélèvement d'N par les végétaux s'établit à 2% et 7% respectivement pour l'apport injecté et en surface. Le pourcentage de recouvrement de l'N marqué apporté s'établit à 76% pour l'apport par injection et à 53% pour l'apport en surface

Contribution du traçage isotopique 15N à l'étude du devenir des émissions azotées gazeuses du lisier

15N tracer techniques are usually recognised as a unique tool to follow nitrogen turn-over from soil-plant studies, particularly from nitrogen fertilizer applications, they remain poorly documented in studying losses from animal manures. Direct labelling of animal manure with 15N is possible by incorporating 15N into animal feed, but is very expensive, labor intensive and time consuming. It is however particularly relevant when the organic N fraction is investigated. More frequently, authors labelled the NH4+-N pool of a slurry by adding a small amount of highly enriched NH4+-N. Moal et al conducted a preliminary study that demonstrated that the added N behaves as the endogenous NH4+ initially present in the slurry. This abstract describes field and laboratory 15N balance studies conducted to determine the fate of labelled ammonium sulphate into a pig slurry.L'utilisation de l'isotope stable 15N est largement répandue pour l'étude du devenir de l'azote - dans le système sol-plante - des fertilisants chimiques. Peu d'études ont été conduites pour l'étude du devenir de l'azote des lisiers à l'aide de l'outil isotopique. Ce résumé illustre différentes applications du traçage isotopique 15N pour l'étude du devenir de l'azote des lisiers, à la fois des émissions d'ammoniac après épandage et des processus de nitrification dénitrification

Utilisation de l'isotope 15N pour la détermination de la source de protoxyde d'azote (nitrification et dénitrification) au cours du traitement aérobie du lisier

International audienceIn order to elucidate and quantify nitrogen transformations occurring during aerobic treatment of pig slurry, two laboratory experiments were carried out with contrasting levels of aeration, high level of aeration (experiment 1) and low level of aeration (experiment 2). During these experiments, after reaching steady state conditions, a single pulse of NO3--15N tracer was added directly in the reactor. When nitrification conditions were prevailing (experiment 1), no transformation of added NO3--15N occurred (98.7% 15N-recovery as nitrates in the liquid slurry). Moreover, the unlabelled nitrous oxide (N2O) measured (7.4% of the total nitrogen content of the raw slurry) strongly demonstrated that the source of N2O emitted was nitrification. During simultaneous nitrification and denitrification conditions (experiment 2), the added NO3--15N was found in gaseous nitrogen forms (N2O-15N: 27%; N2-15N: 18%) and in the liquid (TN-15N: 54%). From this result, it was evident that N2O was mainly emitted by denitrification process. Using the decrease of the isotopic excess of the NO3--15N we calculated that 92% of NO2-- N was directly denitrified (as gaseous forms) without any previous oxidation to nitrate.Afin de quantifier les transformations de l'azote au cours du traitement aérobie du lisier de porc, 2 essais en laboratoire ont été effectués en utilisant des niveaux d'oxygénation fort (essai 1) et faible (essai 2). Au cours de ces expériences, après avoir atteint l'équilibre dans le réacteur, une faible quantité de 15N- NO3- a été ajoutée dans le réacteur. Lorsque les réactions de nitrifications sont favorisées (essai 1), aucune transformation du 15N- NO3- n' a été observée (recouvrement de 98.7% du 15N- NO3- ajouté). De plus, le protoxyde d'azote émis était non marqué, ce qui prouve que la principale source de N2O était, dans ces conditions, la nitrification. Lorsque la nitrification et dénitrification simultanées sont favorisées (essai 2), le 15N- NO3- ajouté se retrouve partiellement sous forme gazeuse (N2O-15N: 27%; N2-15N: 18%) et sous forme liquide. D'après ces résultats, il apparaît que dans ces conditions, la principale source de N2O est la dénitrification. En utilisant les équations relatives à la dilution isotopique, nous avons calculé que 92% des nitrites étaient directement dénitrifiés (sous forme gazeuse) sans oxydation préalable en nitrates

Marquage de l'azote du lisier de porc par ajout direct de sulfate d'ammonium : une expérience en laboratoire de la volatilisation de NH3

International audienceThe addition of exogenous ammoniacal nitrogen to slurry can be used to study the influence of ammoniacal nitrogen concentration or the presence of different ions on ammonia emissions. This preliminary study aimed to test the validity of such a direct incorporation of ammonium salts to slurries in relation to ammonia volatilization. It was conduted using cylindrical glass volatilization chambers an 15N-labelling techniques. Labelled pig slurry was prepared by direct addition of 15N-(NH4)2SO4(15N-AS). The fate of total ammoniacal nitrogen was followed for 48 h from surface application to soil. The analysis of isotopic excess (E%) of volatilized ammonia 0.25, 2, 6, 12, 24 and 48 h after labelled slurry application suggested that the added N4+ behaved as the endogenous NH4+ initially present in the slurry. An average TAN-15N (total ammoniacal nitrogen) recovery of 97.5% (CV 2%) was obtained. During this study, no immobilization or nitrification of slurry-derived nitrogen was noticed.Description d'une procédure de marquage de l'azote du lisier par ajout direct de sulfate d'ammonium enrichi en N15 au cours d'une étude cinétique de volatilisation de l'azote des lisiers

Nitrification activity of soil polluted with copper and zinc after intensive pig slurry application

Nitrate pollution is a big hazard around industrial pig farms. It is possible to manage this problem by the help of soil filtering plots. The SOLEPUR treatment represents a soil purifying system for treatment of pig slurry using soil physical and chemical capacities succeeded by denitrification of nitrogen in leachates. The SOLEPUR process was described in detail in a previous paper (Martinez, 1997). After intensive application of pig slurry, pollution by Cu and Zn is observed. High concentrations of heavy metals can perturb the soil nitrogen cycle (Wilson, 1977). Premi and Cornfield (1969) reported that soil Zn concentrations of 100, 1000 and 10 000 μg Zn g-1 (as ZnSO4) showed no, partial and complete inhibition of nitrification, respectively. The aim of our study was to determine the threshold of heavy metal (Cu, Zn) concentrations in soil of the SOLEPUR treatment facility beyond which nitrification will be inhibited, thereby interrupting the purifying capacity of this soil based system

Transformations de l'azote au cours du stockage anaérobie de lisier marqué au 15N

International audienceDifferent forms of nitrogen : dissolved inorganic-N (or total ammonium-N), suspended organic-N and dissolved organic-N were followed during anaerobic storage of N-15 labelled pig slurry. The kinetics of nitrogen transformations were recorded at 0, 1, 3, 7, 14, 28, 63 and 84 days during a laboratory incubation. At day O, 15N enriched urea (150 mgN/kg of slurry with a isotopic excess of 50%) was added to the slurry. After a rapid total hydrolysis of the urea (within 1 day), a continuous decay of the suspended organic-N fraction was observed concurrently with the increase in the total ammonium-N pool. This mineralization reached 19% of the initial total organic-N fraction, resulting in an increase of the total ammoniacal nitrogen content from 2 410 to 2 780 mgN-NH4+/kg of slurry. Labelling techniques allowed measurement of a simultaneous slight immobilization (into the suspended organic-N fraction) of 4.6 % of the initial ammoniacal-N.L'évolution de différentes formes azotées : N-minéral dissous (i. e. azote ammoniacal), N-organique en suspension et N-organique dissous a été suivie au cours du stockage anaérobie du lisier de porc. Après une hydrolyse rapide de l'urée enrichie en 15N (moins de 1 jour), une minéralisation continue de la fraction N-organique en suspension a été observée et simultanément une augmentation du pool d'azote ammoniacal, qui passe de 2 410 à 2 780 mg N-NH4+/kg de lisier. L'utilisation d'azote marqué permet de mesurer une immobilisation faible de l'orde de 4,6% de l'azote ammoniacal total initial