| The experiment was conducted with one grassland plot in natural restoration process in Ansai, which was located in Loess Hilly Region. The CO2flux, energy flux, meteorological factors, soil moisture, soil temperature, and soil heat flux was observed. The observation of CO2flux, energy flux was based on open-path eddy covariance method. The growing season of the grassland was divided into four periods-germination period, initial growing period, vigorously growing period and declining period. In different periods, biomass factors and soil nutrient contents were investigated. Using the combination method of continuous measuring and periodic measuring, it analysed the daily and seasonal variation of CO2flux, the change of meteorological factors, soil factors, biomass factors. It also discussed the major factors influencing the CO2flux. At last, it calculate the monthly CO2flux and yearly CO2flux. The main results were shown as follows:1) Daily variation of CO2flux of grassland communityIn the growing season of grassland, CO2flux at night or in the daytime of every month obeyed certain regularities. In the daytime, it presented a single peak curve. It changed from releasing carbon to absorbing carbon between7:00and8:30and it reversed between17:30and18:30. CO2absorption peaks appeared between11:30and13:30and it did in advance at first, then delayed as the growth of grass. The maximum rate of CO2absorption was0.9266mgCO2·s-1in August. At night, the maximum value of CO2flux presented itself between21:00and22:00. From April to October, the appearance time of the maximum value in each month delayed at first and was in advance then. The maximum value of the CO2flux peak showed in August and the value was0.2131mgCO2·m-2s-1. CO2flux increased before the maximum value.After it, CO2flux first increased, then experienced a stable period, and decreased again between4:00and6:00. 2) Seasonal variation of CO2flux of grassland communityIt showed some differences between total CO2flux at night, total CO2flux in the daytime and daily CO2flux in the growing season and in the non-growing season. In the growing season, total CO2flux at night increased at first, then decreased, and the maximum value was16.0358gCO2·m-2·d-1in August. The variation of total CO2flux in the daytime and daily CO2flux were just opposite to it at night. Both of their minimum value in August were-48.9550gCO·m-2d-1,-40.8067gCO2·-2d-1, respectively. In the non-growing season, total CO2flux at night decreased from November and reached the minimum value at the end of December. Then it kept relatively stable. Total CO2flux in the daytime and daily CO2flux remain stable in November and December, then decreased, and increased from February. At the end of March, it changed into negative value.3) Relationship between meteorological factors and CO2fluxEach meteorological factor had different role in influencing the daytime CO2flux in the growing season and in the non-growing season and night CO2flux. For daytime CO2flux in the growing season, they were solar radiation, air humidity at the height of lm, latent heat flux and sensible heat flux. Solar radiation played an indirect role in CO2flux through latent heat flux, while the effects of the others were direct. For daytime CO2flux in the non-growing season, they were solar radiation and sensible heat flux and the former performed an indirect function through the latter. For CO2flux, they were air temperature and humidity at the height of lm, latent heat flux and sensible heat flux. They all affected CO2flux directly.4) Relationship between soil factors and CO2fluxThere were significant correlation between the daytime CO2flux in the growing season and night CO2flux with temprature of soil in the layer of0-10cm and volumetric water content of soil in the layer of0-20cm(P<0.05). the daytime CO2flux in the non-growing season was only significantly related to temperature of soil in the layer of0-10cm(P<0.01). The results of regression analysis between soil nutrient elements and CO2flux showed that factors impacting CO2flux greatly were the0-10cm soil organic matter content, the10-20cm soil total N content, the80-100cm soil total N content and80-100cm soil total P content. The level of correlation between CO2flux and the20-40cm soil organic matter content, the0-10cm soil total N content and the10-20cm soil total P content is rather low.5) Relationship between biomass and CO2flux CO2flux were negatively related to aboveground living biomass(P<0.01,r=-0.990) and positively related to aboveground dead biomass(P<0.01,r=0.991). The results of regression analysis between CO2flux with aboveground living biomass and aboveground dead biomass showed that the linear correlation between them were striking(P<0.05). The variation of CO2flux can be nicely explicated by the two factors(R2=0.999).6) The characteristic of grassland as carbon sink or sourceGrassland was acting as carbon source in the non-growing season and as carbon sink in the growing season. Monthly CO2flux increased from November to December, then decreased until August,and increased again after August. The value of monthly CO2flux in December was the maximum and it was7.01gCO2·m-2·month-1. The minimum appeared in August and was511.54gCO2·m-2·month-1. In the whole year, grassland represented as carbon sink and absorbed1397.93gCO2per square meter. |
PDF Full Text Request