Functions of Calcium-bound Phosphorus in Relation to Characteristics of Phosphorus Releasing Bacteria in Sediment of a Chinese Shallow Lake (Lake Wabu)

摘要

Sediment phosphorus (P) release accelerates lake eutrophication, while retention capacity and release potential of different P fractions, calcium-bound P (CaCO3 approximate to P) in particular, still remains unclear. Fractionation and sorption behaviors of phosphorus were studied in sediment of a Chinese shallow lake (Lake Wabu) and two inflowing rivers from December 2011 to December 2012. Abundance of P releasing bacteria was analyzed, and their main species were isolated using a culture-dependent method and identified by their 16S rDNA sequences. CaCO3 approximate to P release abilities of these bacteria were also tested. In sediments of both the lake and rivers studied, the rank order of the different P extracts was CaCO3 approximate to P > iron-bound P > acid-soluble organic P > hot NaOH-extractable organic P. At the same time, CaCO3 approximate to P content and equilibrium P concentration (EPC0) values in river sediments were significantly higher than those in the lake. Additionally, EPC0 changes non-monotonically with increasing CaCO3 approximate to P content, forming a V-shaped curve, with the lowest EPC0 at an intermediate CaCO3 approximate to P content (around 180mg kg(-1)). Below this threshold, CaCO3 approximate to P was a component strengthening P retention; moreover, CaCO3 approximate to P became an active species responsible for P release. Noticeably, between the two parts divided by this threshold, the differences in abundance of inorganic phosphorus solubilizing bacteria (IPB) and organic phosphorus mineralizing bacteria (OPB) were insignificant and the dominant IPB species clustered together. By contrast, OPB was distinguished from each other, whose dominant species isolated from the part with higher CaCO3 approximate to P content, namely Novosphingobium sp., exhibited a stronger ability to solubilize CaCO3 approximate to P. Shortly, with lower content, CaCO3 approximate to P tends to stabilize P in sediment; while with higher content or under eutrophic condition, it shifted into P source, with some OPB species becoming the main factors to drive its release.