探明土壤磷素的存在形态, 有助于揭示其在环境中的累积、 迁移和转化过程及生物有效性。 目前, 在大尺度样带上开展土壤磷素形态空间变异规律的研究较少。 本研究中, 沿纬度方向采集了我国东部不同气候带分布的7种地带性林地土壤(包括寒温带的棕色针叶林土、 中温带的暗棕壤、 暖温带的棕壤、 北亚热带的黄棕壤、 中亚热带的黄壤、 南亚热带的赤红壤和热带的砖红壤), 将化学浸提法与溶液磷-31核磁共振(³¹P NMR)波谱法相结合, 分析了土壤中磷素形态以及与其他土壤性质之间的关系, 以期为阐明土壤磷素形态的空间变异性及其驱动因素提供基础资料。 结果表明: 供试土壤中, 全磷、 有效磷、 无机磷和有机磷的含量范围分别为179.8~825.2, 2.41~15.3, 92.6~351.2和14.7~474.4 mg·kg^-1, 其中活性、 中等活性、 中等稳定性和高稳定性有机磷组分的含量范围分别为1.38~30.9, 8.63~213.7, 3.01~32.2和1.73~199.2 mg·kg^-1。 根据溶液³¹P NMR波谱, 鉴定出供试土壤中含有无机形态的磷素即正磷酸盐和焦磷酸盐, 同时也鉴定出了磷酸单酯、 磷酸二酯和膦酸盐等有机形态磷素的存在, 其中磷酸单酯中又鉴定出了新-肌醇六磷酸、 D-手性-肌醇六磷酸、 RNA单核苷酸、 α-磷酸甘油、 肌-肌醇六磷酸、 β-磷酸甘油和鲨-肌醇六磷酸, 磷酸二酯中又鉴定出了DNA的存在; 所有土壤中均未检测出多聚磷酸盐的存在, 除棕色针叶林土和暗棕壤外的其他土壤中未检测出膦酸盐的存在, 而赤红壤中未检测出DNA的存在; 无机形态的磷素以正磷酸盐为主, 而有机形态的磷素则以磷酸单酯为主。 总体来看, 无论化学浸提法还是溶液³¹P NMR波谱法, 从寒温带的棕色针叶林土到热带的砖红壤, 全磷、 有效磷、 无机磷、 有机磷及其组分的含量均呈现下降趋势。 溶液³¹P NMR波谱与化学浸提法鉴定的磷素形态之间存在相关关系, 其中正磷酸盐与活性有机磷的关系最为密切, 磷酸单酯和膦酸盐与中等活性有机磷的关系最为密切, 而焦磷酸盐和磷酸二酯与中等稳定性有机磷的关系最为密切。 与化学浸提法相比, 溶液³¹P NMR波谱法能从详细的分子水平上揭示土壤磷素形态的空间变异规律。

Understanding the forms of phosphorus present in soil is important for elucidating its accumulation, migration, transformation, and bioavailability in the environment. At present, however, studies on the spatial variability of different forms of phosphorus in soil across large-scale transects are rare. In the present study, seven zonal forest soils from sites across different climatic zones were collected along a latitudinal transect in eastern China. The soils used included brown coniferous forest soil from the cold temperate zone, dark brown soil from the middle temperate zone, brown soil from the warm temperate zone, yellow brown soil from the northern subtropical zone, yellow soil from the middle subtropical zone, lateritic red soil from the southern subtropical zone, and latosol from the tropical zone. A chemical extraction method was combined with solution phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectroscopy to analyze the phosphorus forms present in the soils and determine their relationships with other soil properties. The concentrations of total phosphorus, available phosphorus, inorganic phosphorus, and organic phosphorus in the tested soils ranged from 179.8 to 825.2, 2.41 to 15.3, 92.6 to 351.2, and 14.7 to 474.4 mg·kg^-1, respectively. The concentrations of four organic phosphorus components (i. e., active, moderately active, moderately stable, and highly stable organic phosphorus) obtained through continuous chemical extraction were 1.38~30.9, 8.63~213.7, 3.01~32.2, and 1.73~199.2 mg·kg^-1, respectively. According to solution³¹P NMR spectra, both inorganic (i. e., orthophosphate and pyrophosphate) and organic (i. e., phosphomonoester, phosphodiester, and phosphonate) forms of phosphorus were identified in the test soils. Moreover, neo-inositol hexakisphosphate, D-chiro-inositol hexakisphosphate, RNA mononucleotides, α-glycerophosphate, myo-inositol hexakisphosphate, β-glycerophosphate and scyllo-inositol hexakisphosphate in phosphomonoesters and deoxyribonucleic acid in phosphodiesters were also identified. In all the tested soils, polyphosphate was not detected. Phosphonate was not detected in the soils except in brown coniferous forest soil and dark brown soil, whereas deoxyribonucleic acid was not detected in lateritic red soil. Inorganic phosphorus was dominated by orthophosphate, while organic phosphorus was dominated by phosphomonoester. In general, regardless of whether chemical extraction or solution³¹P NMR spectroscopy, the concentrations of total phosphorus, available phosphorus, inorganic phosphorus and organic phosphorus and its fractions tended to decrease from brown coniferous forest soil in the cold temperate zone to latosol in the tropical zone. There was a correlation between phosphorus forms identified using solution³¹P NMR spectroscopy and those identified using chemical extraction method. Orthophosphate was most closely related to active organic phosphorus; phosphomonoester and phosphonate were most closely related to moderately active organic phosphorus; and pyrophosphate and phosphodiester were most closely related to moderately stable organic phosphorus.³¹P NMR spectroscopy is a more effective method than chemical extraction to understand the spatial variability in soil phosphorus at a detailed molecular level.