| The authors take the rice season of Rice-wheat rotation system near Tai Lake as the object and establish an empirical model for determining net CO2 emission from a paddy rice ecosystem using techniques of static transparent and opaque chambers. Then the model is applied to estimate the hourly net ecosystem exchange (NEE) of a normal rice paddy field at a suburb of Wuxi, Jiangsu province during the entire rice season.The modeling results show the seasonal variation of NEE from the paddy rice ecosystem in Wuxi in the rice season of 2003. Fractional net CO2 emission occurred during the riving and the early tillering stage. Net CO2 fixation occurred in the later tillering, panicle initiating and heading stage and daily mean net flux of CO2 fixation appeared with an increasing trend as rice growing. The maximum of net flux of CO2 fixation occurred in the panicle initiating stage. A decline trend in the net flux of CO2 fixation was documented after the heading stage and therefore net CO2 emission occurred in the maturing stage. The daily mean NEE of the investigated rice paddy field are on average 0.4-0.5, -2.8-3.2, -12.0-13.7, -7.8-8.9, 2.7-3.1, and 1.0 -1.1 g CO2 m2 d-1 in the riving, tillering, panicle initiating, heading, flowering and maturing stage, respective, hi the rice season of 2003, with an seasonally accumulative NEE of-1424-1632 kg Cha-1.The R and NEE estimated using the empirical model fit the R and NEE observed in the field using techniques of static transparent and opaque chambers leasonably well. The diurnal and seasonal variations of NEE estimated using the empirical model are consistent with those observed by other researchers using the methods of eddy covariance and relax eddy accumulation. These suggest that the NEE estimated using the empirical model established in this study is reliable and the empirical model can accurately determinate the actual variations of R and NEE in the field. |
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