Net Ecosystem CO2 Exchang and Controls of a Subtropical Manilagrass Lawn
|School||Fujian Normal University|
|Keywords||manilagrass artificial-lawn net ecosystem CO2 exchange infrared gas analyze method gas chromatogram method|
This study focused on the manilagrass lawn in the Minjiang Park of Fuzhou city, Fujian,China.A comparison was made between--chamber/infrared gas analyze method（IRGA method） and static chamber/gas chromatogram method（GC method） in evaluating CO2 net ecosystem exchange（NEE）.The diurnal and seasonal variation of net ecosystem exchange（NEE） in manilagrass lawn ecosystem and its carbon balance components were also measured.The relationships were analyzed between the NEE of manilagrass lawn ecosystem and its various factors（environmental factors and human managements such as clipping and irrigation）.Then the annual NEE rate was estimated. The major results were followed:1) The disturbance to natural conditions in the IRGA chamber was weaker than that in the GC chamber.The values of the NEE rate measured by IRGA method were closer the ture values than that by GC method,but the results were strongly correlated.2) The diurnal variation of NEE showed a unimodal pattern in lawn ecosystem.In the daytime,CO2 absorptions by lawn ecosystem were the strongest around at noon when it had the highest photosynthetically active radiation.While in the nighttime,lawn ecosystem emitted CO2 at low rate.In addition,the ecosystem respiration rates measured at 7:00 could well represent the average flux value for the whole day.3) The lawn ecosystem could uptake CO2 in both summer and winter,even in the coldest February.However,the rate of absorption in summer was generally higher than that in winter.4) The stepwise regression analysis showed that the key factors that controlled the diurnal variation of NEE were photosynthetically active radiation,air temperature and soil moisture.The principal component analysis discovered that the major factors of the seasonal variations of NEE were the observation indexes,which related to moisture temperature and light.5) The clipping plot promoted NEE rate mainly through reduing the gross canopy photosynthesis rates of lawn,while the irrigation plot increased NEE rate by promoting the respiration rate.The clipping effect had lasted about three months,during this period, it emited 202.20 g C·m-2 into the atmosphere.Irrigation at different times had different effects on ecosystem respiration.The increase of the respiration resulted from the artificial irrigation at 18:00 was much smaller than that of the artificial irrigation at 6:00 because the soil moisture was much higher at 18:00 than that at 6:00.6) Based on multi-factor modifying Michaelis-Menten model,the annual NEE flux in lawn was estimated which was -329.04 g C·m-2.yr-1.However,the annual NEE flux was -126.84 g C·m-2·yr-1(-1.27 t C·hm-2·yr-1),if the carbon loss was added due to clipping.