Soil organic matter transformations induced by Hieracium pilosella L. in tussock grassland of New Zealand

 To study the effect of Hieracium pilosella L. invasion on the transformations of soil organic matter of New Zealand tussock grassland soils (Ustochrepts), plant material and soils underneath Hieracium, the surrounding halo, and the adjacent herbfield (depleted tussock grassland) were examined for their chemical composition. An attempt was made to reveal possible changes in chemical composition of the soil organic matter induced by H. pilosella invasion. Small differences were detected by solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy in the composition of the plant and soil materials from these zones. Most of the differences in soil organic matter occurred due to differences in the amount and quality of plant-residue inputs. Comparable amounts of phenolic C were detected in the solid-state ¹³C NMR spectra of H. pilosella and herbfield vegetation, while alkaline CuO oxidation yielded considerable lower lignin oxidation products for H. pilosella. A slightly higher proportion of these compounds in H. pilosella soil revealed an accumulation and a low degradation rate of lignin compounds under H. pilosella. The HCl hydrolysis and solid-state ¹⁵N NMR spectroscopy showed similar chemical compositions of the N fractions of the three different soils. The absence of ¹⁵N NMR signal intensity assignable to aniline derivatives or aromatic heterocyclic N indicates that the condensation of phenolic compounds with N groups plays a minor role in N sequestration in these soils. Received: 6 September 1999