Immobilization of ¹⁵ N in forest litter studied by ¹⁵ N CPMAS NMR spectroscopy

Abstract

Abstract Solutions labelled with 15 N were applied as ( 15 NH 4 ) 2 SO 4 or K 15 NO 3 to isolated microplots in the floor of mountain beech forest (Nothofagus solandri var. cliffortioides) and incubated for 135 days under field conditions of moisture and temperature. Solid state 15 N CPMAS NMR spectra of the forest litter layer showed that more than 80% of the total signal intensity was attributable to the secondary amide‐peptide peak. The degree of 15 N enrichment or form of N did not alter the relative intensity of signals attributable to 15 N in peptides, nucleic acids and aliphatic amine groups (amino sugars and free NH 2 on amino acids). Combinations of 13 C and 15 N‐NMR spectra, edited by a process that exploited differences in proton spin properties between distinct categories of organic matter, indicated incorporation of 15 N in humified organic matter rather than partly degraded plant material. This application demonstrated that solid state 15 N CPMAS NMR has potential for use in studies of N immobilization under field conditions and with materials containing little N and small 15 N enrichment.