Organic phosphorus fractionation in wetland soil profiles by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy

摘要

Organic P (OP) plays an important role in soil P cycling and is a potential P source for wetland plants. In this study, a modified chemical sequential fractionation method and 31P nuclear magnetic resonance spectroscopy (~(31)P NMR) of NaOH-EDTA extracts were used to examine the distribution of organic P fractions and compounds in soil profiles of the Beijing Yeyahu Wetland, China. The influence of acid treatment prior to NaOH-EDTA extraction on ~(31)P NMR spectra was also investigated. Results show that highly resistant OP was the major class of organic P. The rank order of organic P fractions was highly resistant OP (on average accounting for 68.5% of total OP)>moderately resistant OP (15.8%m of total OP)>moderately labile OP (11.4% of total OP)>labile OP (4.3% of total OP). Most of the organic P fractions decreased with soil depth due to the accumulation of plant residues in surface soils and the deposition and diagenesis of soils. Moderately (r=0.586, p<0.01) and highly (r=0.741, p<0.01) resistant OP fractions were positively correlated with soil organic matter. Phosphorus compounds including orthophosphate (23-74.6% of total P in spectra), monoester phosphate (18.6-76%), diester phosphate (nil-7.8%) and pyrophosphate (nil-6.7%) were characterized using ~(31)P NMR. Monoester-P was the dominant soil organic P compound identified. The proportion of monoester-P increased significantly in NaOH-EDTA extracts with HCl pretreatment and it was confirmed by chemical analysis. Therefore, it can be concluded that HCl pretreatment can remove more than half of the inorganic P and increase the overall recovery rate of organic P during subsequent NaOH-EDTA extraction, which might be a new approach for organic P detection. Furthermore, the OP chemical sequential fractionation method presented in this study is an integrated and comprehensive approach which can be used for further verification.