土壤碳酸氢钠提取态无机磷酸盐中氧同位素分析  

Analysis of the oxygen isotopic composition of inorganic phosphate extracted from soils with NaHCO_3

作　　者：温云杰 刘荣乐[2] 汪洪[1] 

机构地区：[1]中国农业科学院农业资源与农业区划研究所耕地培育技术国家工程实验室农业部植物营养与肥料重点实验室,北京100081 [2]中国农业科学院研究生院,北京100081

出　　处：《环境科学学报》2017年第1期326-331,共6页Acta Scientiae Circumstantiae

基　　金：国家重点基础研究发展计划(973计划)(No.2013CB127402)~~

摘　　要：土壤中碳酸氢钠提取的无机磷(Olsen-P)是可被植物吸收利用的有效磷.利用磷酸盐中^(18)O和^(16)O组成(δ^(18)O-P)开展土壤磷来源示踪和磷循环转化,具有重要意义.选择0.5 mol·L^(-1)Na HCO_3(pH 8.5)溶液并加入无磷活性炭提取土壤磷,通过Mg(OH)_2-PO_4共沉淀、磷酸铈沉淀等过程分离纯化其中磷酸盐,获得磷酸银沉淀,利用元素分析仪-稳定性同位素比例质谱仪测定氧同位素组成δ^(18)O-P值.结果表明:分离纯化沉淀3个关键过程中磷酸盐的回收率均能达到93%以上,损失较少,未出现氧同位素分馏.X射线衍射仪和氧含量测定表明,实验获取的磷酸银样品纯度较高.加入无磷活性炭可有效去除有机质对δ^(18)O-P测定影响.供试黑土和潮土中碳酸氢钠提取态土壤无机磷酸盐δ^(18)O-P值分别为17.64‰±1.03‰和18.20‰±0.83‰,差异不明显.本文建立土壤碳酸氢钠提取态无机磷酸盐中氧同位素分析测定方法,为农田土壤中磷的循环转化及其溯源研究提供技术支撑.The ratio between the heaviest and lightest oxygen isotopes（18O and 16O） in phosphate,i. e. the oxygen isotope composition of phosphate（ δ18O-P）,is widely used to study phosphorus（ P） cycle and transformations in soils. In this study,we used 0.5 mol·L-1 NaHCO3（ pH 8.5） combined with the activated carbon without P to extract soil available P（ Olsen-P）. Phosphate in the extract solution was co-precipitated with magnesium hydroxide and further purified through cerium phosphate precipitation and resin separation. It was ultimately converted to silver phosphate. Silver phosphate samples were pyrolitically decomposed to carbon monoxide and analyzed for δ18O by elemental analyzer-stable isotope ratio mass spectrometer. The results showed that P recovery rate in the process of three key purification precipitations was more than 93%,indicating less phosphate loss. There was no isotope fractionation during extraction and purification. The obtained silver phosphate sample had high purity according to X-ray diffraction and oxygen content determination. Activated carbon without P could alleviate the influence of oxygen in soil organic matter on the determination of δ18O-P values. The δ18O-P values in fluvo aquic soil and black soil were 18.20‰±0.83‰ and 17.64‰±1.03‰,respectively. This study established a method for analyzing δ18O-P of inorganic phosphate extracted from soils with NaHCO3,which could be used to trace P sources and to determine the extent of P cycle in soil.

关 键 词：土壤磷 氧同位素 稳定性同位素 

分 类 号：X53[环境科学与工程—环境工程]