Η μελέτη της νιτροποίησης στα φυσικά εδαφολογικά συστήματα είναι σημαντική όχι μόνο για αγρονομικούς λόγους αλλά και λόγω των αποτελεσμάτων της στο περιβάλλον. Δεδομένου ότι τα λιπάσματα της ουρίας και αμμωνίου περιλαμβάνουν τον συνολικό όγκο των λιπασμάτων που χρησιμοποιούνται στην παγκόσμια γεωργία, το ποσοστό νιτροποίησης είναι ένας βασικός παράγοντας που καθορίζει τις πιθανές απώλειες του Ν. Συσσωρευμένο NO3 μπορεί να μειωθεί από το εδαφικό οικοσύστημα μέσω της διύλισης και της διάσπασης νιτρικών, οι οποίες προκαλούν τη ρύπανση των υδάτων εδάφους και επιφάνειας και τις αεριώδεις εκπομπές στη ατμόσφαιρα Η παρούσα εργασία ασχολήθηκε με την νιτροποίηση, (βιολογική οξείδωση της αμμωνίας) που υλοποιείται από δύο διαφορετικές κατηγορίες αυτότροφων βακτηριών. Η πρώτη ομάδα (νιτρωδοποιητές) μετατρέπει την αμμωνία ( ) σε νιτρώδη ( ) και στη συνέχεια η δεύτερη ομάδα, οι νιτρικοποιητές, οξειδώνει περαιτέρω το ενδιάμεσο προϊόν σε νιτρικά. Ακολούθως προαιρετικά αερόβιοι ετερότροφοι μικροοργανισμοί με τη βοήθεια οργανικής πηγής άνθρακα σε αναερόβιο περιβάλλον μετατρέπουν το νιτρικό άζωτο σε αέριο άζωτο (απονιτροποίηση). Το στάδιο της απονιτροποίησης δεν θα μας αποασχολήσει στην παρούσα εργασία. Τα βακτήρια που είναι υπεύθυνα για την οξείδωση της αμμωνίας είναι τα (ammonium oxidizing bacteria) ή νιτρωδοβακτήρια, ενώ τα βακτήρια που οξειδώνουν τα νιτρώδη σε νιτρικά είναι τα νιτρικοβακτήρια. Βακτήρια των γενών Nitrosomonas συμμετέχουν στο πρώτο στάδιο της νιτροποίησης. Στο δεύτερο στάδιο περιλαμβάνεται το γένος Nitrobacter. Με μια σειρά πειραμάτων φυσικού και τεχνητού χώματος, με την παρουσία ή μη μικροοργανισμών, μελετάμε την κινητική της νιτροποίησης και τους παράγοντες που ενδεχομένως επιδρούν στην κινητική αυτή, καθώς και τους παράγοντες που παρεμποδίζουν την νιτροποίηση. / The study of nitrification in the natural soil' systems is important not only for agronomic reasons but also because of its potentials effects on the environment. Since urea and ammonium fertilizers comprise the bulk of total fertilizer N uzed in world agriculture, the rate of nitrification is a basic factor determining potential losses of N. Accumulated NO3 can be depleted from the grassland ecosystem via leaching and denitrification, which cause ground and surface water pollution and gaseous emissions to the atmosphere. The present work is about the nitrification, (biological oxidation of ammonia) that is materialized by two different categories of autotrophic bacteria. The first group (ammonia oxidizers) converts ammonium ( ) to nitrite ( ), then the second group, nitrite oxidizers, oxidizes further the intermediate product to nitrate. Denitrification is the biological process, which is responsible for the removal of nitrogen in the form of nitrate and/or nitrite by conversion to nitrogen gas. The stage of denitrification won’t occupy us in the present work. The bacteria responsible for biological oxidation of ammonia are (ammonium oxidizing bacteria), while the bacteria that oxidize nitrite to nitrate are nitrite oxidizers. Bacteria of genders Nitrosomonas participate in the first stage of nitrification. In the second stage the gender Nitrobacter is included. With a row of experiments including natural and artificial soil, and with the presence or not of micro-organisms, we study the kinetics of nitrification and the factors that potential influence this kinetics, as well as the factors that impede the nitrification.

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Several nitrogen fixers were isolated from the roots and rhizosphere of Quebec crops. Many of these nitrogen fixers were discarded when the production of N(,2)O in the presence of C(,2)H(,2), as a test for denitrifying ability, was included as a selected characteristic. Further characterization of the Nir('+) strains showed that they were Azospirillum lipoferum. / The cytochrome composition of Azospirillum brasilense (a denitrifier) grown under various conditions in a defined medium was investigated. Optical absorbance difference spectra of the particulate fraction of cells grown under aerated conditions indicated the presence of cytochromes of type b, c and a+a(,3). Under low aeration there was a quantitative increase in cytochromes b and c with a concomitant decrease in the a+a(,3)-type cytochrome. At high aeration, a CO spectrum indicated the possible participation of an o-type cytochrome. / At both high and low oxygen concentrations, the supernatant fraction revealed only one c-type cytochrome. Its abundance was increased at low oxygen concentrations. / Cytochrome spectra of anaerobically grown cells using different nitrogen oxides (NO(,3)('-), NO(,2)('-) and N(,2)O) as final electron acceptors revealed the presence of the different cytochromes involved in anaerobic respiration. The reduction of NO(,2)('-) was associated with the cytochrome cd (peak at 620 nm) found only in the supernatant fraction of NO(,2)('-)-grown cells. / Growth on NO(,3)('-) was characterized by a diauxic type of curve in which the first logarithmic phase corresponded to the reduction of NO(,3)('-). The second logarithmic phase corresponded to the reduction of NO(,2)('-). / Growth of Azospirillum brasilense with NO(,2)('-) and N(,2)O as final electron acceptor was possible only when a small amount of NO(,3)('-) was present initially. In contrast with other bacteria, growth of Azospirillum brasilense with tungstate instead of molybdate did not result in NO(,3)('-) reductase-deficient cells. / The NO(,2)('-) accumulation observed with NO(,3)('-)-grown cells possibly resulted from the different NO(,3)('-)- and N(,2)('-)-reductase specific activities. However, the longer lag in the NO(,2)('-) reduction when higher concentrations of NO(,3)('-) were used may be due to a direct effect of NO(,3)('-) on the synthesis or activity of the NO(,2)('-) reductase.

Adsorption of the nitrification inhibitors dicyandiamide (DCD) and nitrapyrin (2-chloro-6(trichloromethyl)-pyridine) on humic acid (HA) and fulvic acid (FA) extracted from five Indiana soils was studied. Ten mg of HA or FA were suspended in aqueous solutions (10 ml) of either DCD (5,10, 20, 40 and 80 ug ml-1) or nitrapyrin (2,4,6,8,12 ug ml-1). The amount of nitrification inhibitor absorbed was evaluated after shaking the suspension of DCD for 48 h or nitrapyrin for 24 h. Infrared spectra of the nitrification inhibitor-humic material complexes were recorded. The results indicated that FA adsorbed more DCD than HA, and HA was a better adsorbent for nitrapyrin. Correlation between Freundlich K values and organic carbon content of HA and FA was not statistically significant, indicating a slight contribution of hydrophobic forces in the adsorption of DCD and nitrapyrin. The infrared spectra provided evidence that adsorption occurred predominantly through an ionic bonding mechanism involving the protonated amino group of DCD or the nitrogen of the pyridine ring of nitrapyrin and the negative functional groups of the humic materials. / Department of Natural Resources

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xxii, 212 leaves : ill., graphs ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Biochemistry, 1979

Thesis (M.S. - Agricultural Chemistry and Soils)--University of Arizona. / Includes bibliographical references (leaves 48-50).

Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Biochemisty, 1979.