| Phosphorus (P) is one of the major nutrient-limiting in wetland ecosystem, which is directly related to the productivity of plants. Its oversupply is of great concern in wetlands and aquatic systems due to its role in eutrophication. Beijing Yeyahu Wetland was chosen as a typical wetland in which collected different soil samples from May 2009 to March 2010. Distribution and adsorption characters of phosphorus forms in soils were analyzed, bioavailability was then estimated. Meanwhile, influences of soil physical-chemical characteristics on phosphorus forms were discussed by relativity analysis method.Both inorganic phosphorus (IP) fractionation method and organic phosphorus (OP) fractionation method were optimized in this paper. Through optimum methods, IP was separated as exchangeable phosphorus (Ex-P), iron-bound phosphorus (Fe-P), aluminium-bound phosphorus (Al-P), occluded phosphorus (Oc-P) and calcium-bound phosphorus (Ca-P). OP was separated as labile organic phosphorus (LOP), moderate labile organic phosphorus (MLOP), moderate resistant organic phosphorus (MROP) and highly resistant organic phosphorus (HROP). Distribution characters of various phosphorus forms in soils were as follows:(a) Contents of total phosphorus (TP) in soils were from 376.16 to 638.20 mg·kg-1. Contents of TP were decreased with the increase of soils depth, meanwhile seasonal variation was showed as November> March> May> Septemper. (b) IP was the main form of TP with the contents in soils were from 183.77 to 600.94 mg-kg-1. Ca-P, which content was the highest is relatively steady. Fe-P, Ex-P and Al-P, which contents were in a low lever didn't change with seasons obviously. But Oc-P, which contents changed with seasons, showed as November>March>May>Septemper. (c) The contents of OP in soils were from 40.26 to 328.01 mg·kg-1, only took a little part of TP. Seasonal variation of OP was showed as November> May> March>Swptember, and contents of different parts of OP were in the order:HROP>MLOP>MROP>LOP. The contents of MLOP and HROP decreased in winter obviously which reflected the translation to HROP. (d) The contents of bioavailable phosphorus (BAP) which were from 29.00 to 107.90 mg·kg-1, were in low lever, and their seasonal variation trend of BAP contents was as same as TP.Correlation analysis demonstrated that, pH showed negative correlations with the oontents of Fe-P. Soil moisture content rate showed positive correlations with the content of Oc-P, as well as LOP and MLOP. Organic matter showed positive correlation with the contents of OP. Clay and silt showed positive correlations with the contents of P, while fine sand showed negative correlations.The maximum of IP adsorption capacities were between 18.08 and 68.97 mg·kg-1, and the adsorption on soils were described by second-order kinetics model and modified Langmuir adsorption equation. |
