Seasonal changes of soil phosphorus fractions under Calamagrostis angustifolia wetlands in Sanjiang Plain, China

The seasonal dynamics of soil P fractions was determined in the Sanjiang plain marshes. The soil samples were taken from a depression marsh once or twice every month during the growth season and soil P fractions were determined by the modified Hedley fraction method in 2005. The study showed that P was mainly organically bound in the Sanjiang Plain wetlands. NaOH extractable organic P ( NaOH-Po ) and inorganic P ( NaOH-Pi ) was the predominant form in total organic P (TPo) and total inorganic P (TPi); respectively. The content of Resin-P was highest at end of August and lowest at the early days of July, seasonal dynamic of NaHCO3-Pi and NaOH-Pi were similar to Resin-P. Dil. HCl-Pi and Conc. HCl-Pi had their highest and lowest value at the beginning of September and the initial stage of May. The variation coefficient of ResinP and Conc. HCl-Piwere higher than other Pi fractions, the level of them decreased from the beginning of growth season to the end of growth season, while the other Pi fractions increased i