Chemical nature of soil organic matter under grassland and recently established forest

Carbon-13 (C-13) solid-state NMR spectroscopy was used to investigate the chemical nature of organic C in mineral topsoil sampled under grassland and adjacent recently established (10-17 years old) coniferous forest (Douglas fir, Pseudotsuga menziesii; Ponderosa pine, Pinus ponderosa; Corsican pine, Pinus nigra) at two sites (Craigieburn, Cave Stream) in the South Island of New Zealand. This involved using a Cross-Polarized/Magic-Angle Spinning (CP/MAS) technique to identify different chemical forms of soil organic C, whilst Proton Spin Relaxation Editing (PSRE) was used to determine different 'pools' of soil organic C. Results obtained from the Craigieburn soils (0-5 cm) were more promising than those obtained from the Cave Stream soils (0-10 cm) because the total Fe content was smaller, and indicated a shift towards more recalcitrant forms of organic C in soil under trees compared with grassland, which might reflect reduced inputs of fresh organic matter to the soil under trees.