Estimating Net Primary Productivity and Nutrient Stock in Plant in Freshwater Marsh, Northeastern China

We have investigated the contributions of three dominant macrophyte species Deyeuxia angustifolia Carex lasiocarpa and Carex pseudocuraica (covering about 10 304 km(2)) to carbon (C) nitrogen (N) and phosphorus (P) stocks in the largest freshwater marsh (17 300 km(2)) in China for a 3 year period (from 2002 to 2004) The monthly biomass seasonal and annual net primary productivity (NPP) and nutrient concentrations of three species were measured All three plant species showed rapid growth in the rainy season The maximum and minimum production rates in the freshwater marsh were similar to 36 19 and similar to 9 92 g m(-2) day(-1) respectively The total NPP accounts 1900-2700 g m(-2) year(-1) in the studied area Total organic carbon (TOC) total nitrogen (TN) and total phosphorus (IT) concentrations in roots were higher than those in stem and leaf tissues The vast beds of the three studied species comprise 80% of the grass covered marsh of Sanjiang plain contributing annual nutrient stocks of similar to 10 99 x 10(6) similar to 788 36 x 10(3) and similar to 18 10 x 10(3) t (tonnes) for TOC TN and IT respectively Our results suggest that the nutrient bioaccumulation capacity in freshwater marshes depend mainly on plant species which are decided by hydrological conditions The nutrient stocks in the Sanjiang plain marsh have been greatly reduced because some of the area occupied by C lasiocarpa was replaced by D angustifolia as a result of succession caused by the changes of water table