Tian Liyan, Guo Qingjun, Zhu Yongguan, He Huijun, Lang Yunchao, Hu Jian, Zhang Han, Wei Rongfei, Han Xiaokun, Peters Marc, Yang Junxing
Center for Environmental Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Chaoyang District, Beijing, 100101, China.
University of Chinese Academy of Sciences, Beijing, 100039, China.
Environ Sci Pollut Res Int. 2016 Dec;23(23):23406-23414. doi: 10.1007/s11356-016-7482-7. Epub 2016 Sep 9.
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 (δO) from chemical fertilizers and different fractions (Milli-Q water, 0.5 mol L NaHCO (pH = 8.5), 0.1 mol L NaOH and 1 mol L HCl) of agricultural soils from the Beijing area. The δO results of the water extracts and NaHCO 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 δO value of the water extracts and NaHCO extracts in some soil samples below the equilibrium value may be caused by the hydrolysis of organic P fractions mediated by extracellular enzymes. The δO 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 δO values and highest phosphate concentrations indicated that the HCl fraction was affected by microbial activity. Hence, these δO 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.
农业生态系统中的磷（P）是植物和微生物所必需的有限元素。然而，磷积累以及磷流失所引发的环境问题已变得越来越严重。磷酸盐的氧同位素能够追踪农业土壤中磷的来源、迁移和转化。为了利用磷酸盐氧同位素，需要有合适的从土壤中提取和纯化无机磷酸盐的方法。在此，我们结合两种不同方法来分析来自化肥以及北京地区农业土壤不同组分（超纯水、0.5 mol/L NaHCO（pH = 8.5）、0.1 mol/L NaOH和1 mol/L HCl）的无机磷酸盐的氧同位素组成（δO）。大多数样品中水提取物和NaHCO提取物的δO结果接近计算出的平衡值。这些现象可以通过土壤中快速的磷循环以及化肥的影响来解释。一些土壤样品中水提取物和NaHCO提取物的δO值低于平衡值，可能是由细胞外酶介导的有机磷组分水解所致。NaOH提取物的δO值高于计算出的平衡值，反映了微生物对磷酸盐的吸收与细胞内磷酸盐释放回土壤之间的平衡状态。δO值最低且磷酸盐浓度最高的HCl提取物表明HCl组分受微生物活动影响。因此，这些δO值可能反映了母质的氧同位素值。结果表明，磷酸盐氧同位素分析可能是追踪农业土壤中磷酸盐来源、转化过程及其被微生物利用情况的有效工具。
