Phosphorus (P) in agricultural ecosystems is an essential and limited element for plants and microorganisms. However, environmental problems caused by P accumulation as well as by P loss have become more and more serious. Oxygen isotopes of phosphate can trace the sources, migration, and transformation of P in agricultural soils. In order to use the isotopes of phosphate oxygen, appropriate extraction and purification methods for inorganic phosphate from soils are necessary. Here, we combined two different methods to analyze the oxygen isotopic composition of inorganic phosphate (delta O-18(P)) from chemical fertilizers and different fractions (Milli-Q water, 0.5 mol L-1 NaHCO3 (pH = 8.5), 0.1 mol L-1 NaOH and 1 mol L-1 HCl) of agricultural soils from the Beijing area. The delta O-18(P) results of the water extracts and NaHCO3 extracts in most samples were close to the calculated equilibrium value. These phenomena can be explained by rapid P cycling in soils and the influence of chemical fertilizers. The delta O-18(P) value of the water extracts and NaHCO3 extracts in some soil samples below the equilibrium value may be caused by the hydrolysis of organic P fractions mediated by extracellular enzymes. The delta O-18(P) values of the NaOH extracts were above the calculated equilibrium value reflecting the balance state between microbial uptake of phosphate and the release of intracellular phosphate back to the soil. The HCl extracts with the lowest delta O-18(P) values and highest phosphate concentrations indicated that the HCl fraction was affected by microbial activity. Hence, these delta O-18(p) values likely reflected the oxygen isotopic values of the parent materials. The results suggested that phosphate oxygen isotope analyses could be an effective tool in order to trace phosphate sources, transformation processes, and its utilization by microorganisms in agricultural soils.

Publication name	ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH, 23 (23):23406-23414; 10.1007/s11356-016-7482-7 DEC 2016
Author(s)	Tian, Liyan; Guo, Qingjun; Zhu, Yongguan; He, Huijun; Lang, Yunchao; Hu, Jian; Zhang, Han; Wei, Rongfei; Han, Xiaokun; Peters, Marc; Yang, Junxing
Corresponding author	GUO Qingjun   Guoqj@igsnrr.ac.cn  Chinese Acad Sci, Inst Geog Sci & Nat Resources Res, Ctr Environm Remediat, 11A Datun Rd, Beijing 100101, Peoples R China.
Author(s) from IGCAS	HU Jian

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