Phosphorus (P) is an essential macronutrient for all life forms and often limits the productivity of aquatic and terrestrial ecosystems. P is predominantly derived from the weathering of P-bearing minerals in parent rocks, and the P released could be associated with weathering products, which in turn affects its distribution, speciation and bioavailability in weathering profile. Soil chronosequences across time are analogous to soil profiles across depth regarding weathering, but gravitational movements and plant activities in profiles could also alter element distribution and speciation. However, limited information is available about depth distribution of P species. Therefore, this study characterizes P speciation in a successive weathering profile developed on a granite substrate in Inner Mongolia, northeastern China using a combination of Hedley extraction, <sup>31</sup>P NMR and P and Fe X-ray absorption spectroscopy (XAS). The total P (TP) of the top soil is the highest (0.28%), which decreases with depth up to 30 cm (0.10%) and then increases to 0.27% at 50 cm. Subsequently, TP declines to 0.10% at 110 cm and remains nearly constant up to 290 cm. Preliminary XANES analysis indicates that the proportion of Ca-P decreases from 14.5% in the top soils to 0.5% at 30 cm and then increases to 73.2% at 290 cm. The Al-P proportion decreases from 19.4% to 0 with increasing depth. The Fe-P proportion increases from 48.6% in the top soil to 73.4% at 30 cm, followed by a decrease to 26.8% at 290 cm. Such distribution of P species between 30 and 50 cm could be attributed to a rapid dissolution of Ca-P around 30 cm and subsequent leaching to the underlying horizons. The extraction and NMR analyses are ongoing. This work will improve the understanding of the processes controlling P mobility and distribution in a depth profile.

Distribution and speciation of phosphorus in a granite weathering profile in a temperate climate

253rd National Meeting (2017)

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