Soil phosphorus transformations along two long-term chronosequences with contrasting climate in south-western Australia

Abstract

Background Soil organic phosphorus (P) and its chemical nature change markedly during long-term pedogenesis, but how variation in ecosystem water balance and associated differences in vegetation impact such transformations remain unclear. Methods We used solution P-31-nuclear magnetic resonance (P-31-NMR) spectroscopy to assess the chemical nature of soil organic P along two > 2-million-year coastal sand dune chronosequences in south-western Australia characterised by contrasting ecosystem water balance. We sampled soils from the progressive and retrogressive stages of the ecosystem along the wetter Warren and drier Jurien Bay chronosequences. Results Organic P was a much greater proportion of the total soil P in the wetter Warren than the drier Jurien Bay chronosequence. However, the composition of soil organic and inorganic P detected by P-31-NMR spectroscopy was similar in the two chronosequences. Orthophosphate and simple phosphomonoesters were the dominant P species, and their proportional importance increased as soils aged, constituting > 80% of soil total P in the late stages of pedogenesis. However, no higher-order inositol phosphates were detected along either chronosequence, presumably due to the sandy texture and limited sorption capacity of the soils. Conclusion Our results provide evidence that ecosystem water balance has little impact on the long-term soil organic P transformations during pedogenesis in south-western Australian dune sequences.