Incorporation studies of NH4+ during incubation of organic residues by 15N-CPMAS-NMR-spectroscopy

Abstract

This study focuses on the processes occurring during incorporation of inorganic nitrogen ioto humic substances. Therefore rye grass. wheat straw, beech saw dust, sulphonated Iignin and organosolve Hgnin were incubated toge!her wi!h highly "N-enriched ammonium sulphate in !he laboralory for 600 days. Samples from the incubates were periodical1y anaJysed for weight loss. and carbon and nitrogen contents. The samples were also analysed by solid-state 13C_ and 15N-CPMAS-NMR-spectroscopy to follow !he tumover of the materials during incubation. Mast of the detectable 15N-signals was assigned to amidepeptide stroctures. The remaining intensities could be ascribed to free and alkylated amino groups, and tbose on the low fletd side of the broad amide-peptide signal to índole, pyrrole and nucleotide derivatives. Abiotic reactions of ammonia with suitable precursors and the fonnation of pyridine, pyrazine or phenyloxazone derivatives were nol observed. Signals from ammonia and nitrate occurred only at the end of the ineubation. lntroduc!ion Ammonia-N and its ionized fonn are the most important sources of nitrogen in soils for plants and microorganisms. Ammonia undergoes several biotic and abiotic reactions by which it is immobilized and remobilized from inorganic to organie forms and vice versa duriog langer or shorter periods (Jansson & Persson, 1982). The continuaus exchange between mineral and organic bound N-forms is well estab-Jished. This is also the reason why only 60% or less of fertilizer-N applied to soil is directly taken up by plants, whereas 40-60% ar even more originales from continuously mineralized soil N. Application of 15N_labelled arnrnonia fertilizer showed that afier harvest 50-60% becarne irnmobilized in the soil organic matter (Broadbent & Carlton. 1978). Only during ¡he first or second year did this irnmobiJized N become prefercntially available to plants, and thereafter this residual fertilizer-N behaved like !he bulk of soi! nitrogen (Stevenson & Kelley, 1985). Irnmobilization and mobilization of ammonia depend mainly on the C/N ratio of plant residue during humification. Bacteria and fungi utilize ammonia during lhe degradation of carbonrich plant material mainly as a source of N for the synthesis of their biomass. During prolonged incubation when the cachan source becomes exhausted and the C/N ratio decreases to less than lO, NH3 is released and is present in soi! as NH.t, or afier nitrification as N0 3-. Microorganisms are the catalysts of most transfonnations in soils. In arable soiJs of westem Eurape they contain about 80-120 kg N ha-1 ; but 60-70 times more of organic N (5000-8000 kg N ha-1) is contained in humic components. During a growing season less !han 1 % of !his immobilized N is available to plants. Upon hydrolysis wi!h hot 6 N Hel about 4()...{j0% can be identified as amino acids, amiDo sugars and runmonia, whereas the rest cemmns unknown (Anderson et aJ., 1989). This unknown nitrogen consists of both hydrolysableand nooM hydrolysable-N, but identified and unlmown N participate in !...

Nitrogen Incorporation into Lignite Humic Acids during Microbial Degradation

“…Two other reports also contain 15 N-NMR spectroscopic evidence of ammonia fixation with the formation of 15 N-labeled indole, pyrrole, pyridine, pyrazine, and aminohydroquinone (Thorn and Mikita, 1992;Knicker et al, 1997). In our study, the dominant signal of cHA (-260ppm) 15 N-NMR spectra came from amide-N, which is consistent with an earlier report about the important component in humic substances .…”

Is nitrogen functionality responsible for contrasted responses of riverine dissolved organic matter in pyrolysis?

“…This could be a result of the small quantity of sample available and the rather low signal/noise ratio. In all the spectra, no signal was detected in the chemical shift region of pyridinic N between −25 and −90 ppm [53]. This is in agreement with XPS results, particularly since 15 N NMR has been reported for heterocyclic N underestimation [54] and especially for pyridinic N [45,47].…”

Humic acids buffer the effects of urea on soil ammonia oxidizers and potential nitrification

“…Humic substances can incorporate nitrogen into their structure either directly through chemical reactions or indirectly through microbial activities and subsequent decomposition of microbial biomass (Clinton et al, 1995). Several reports indicate that ammonia–N may be abiotically fixed to soil organic matter, lignin, peat or coal (Nommik and Vathras, 1982; Lapierre et al, 1994; Bosatta and Agren, 1995) when the C/N ratio of plant residue during humification is higher than 10 (Knicker et al, 1997). Thorn and Mikita (1992), using 15 N and 13 C NMR techniques, detected that 15 N-labeled ammonia was incorporated into HAs in the laboratory incubation and that the average N content of HAs increased from 0.88 to 3.17%.…”