Research On Fluxes Of CO₂, N₂O And CH₄ From Grassland Soil-vegetation System In Central Sichuan Hilly Area

Atmospheric greenhouse gases such as CO₂, CH4, N₂O ect increased since industry revolution. Serious global environmental problems, such as sea level rising, vegetation and production change, desertification, and frequently natural disaster ect have already appeared. The global changes will bring about extensive influence on the terrestrial ecosystem system and social economic system necessarily. Since late 70's of 20 centuries, global change research is one of the most important topics. Carbon and nitrogen circling in terrestrial ecosystem is an important part. Cycling of carbon and nitrogen in terrestrial ecosystem is crucial to predict the content of CO₂ and other greenhouse gases in atmosphere in the future.Based on the observation of CO₂, N₂O and CH4 emission from soil-vegetation systems of the wild grassland, clover and perennial ryegrass, diurnal and seasonal variation characteristics, influence factors were discussed in this paper. CO₂, N₂O and CH4 emission was measured by static chamber-gas chromatographic techniques (GC) in the hilly area of the central Sichuan Basin. The main results and conclusions were listed as follows:1) The processes of diurnal and seasonal variations of CO₂ flux in different lawns in mid-Sichuan hilly area had obvious character of single peak. The diurnal variation trend of CO₂ emission fluxes were consistent with temperature; the soil moisture change was quite small at daily scale, generally less than 3%, so the temperature was confirmed as the dominant factor of CO₂ diurnal emission fluxes. Seasonal variation trend of CO₂ emission fluxes from lawns were consistent with changes of temperature and biomass of vegetation. CO₂ emission fluxes of three kinds of lawn were obviously affected by temperature, the correlated coefficient R¹> 0.8 (n=7, p< 0.05). The mid-Sichuan hilly area belongs to Subtropics with moist monsoon climate. Although this area has abundant precipitation, Soil moisture change is not evident and it was in the range of soil moisture that fits soil organic matter decomposed and releases carbon dioxide, influences of soil moisture on CO₂ emission flux were less than temperature's.2) Three kinds of lawn in the hilly area of the central Sichuan Basin ;were a source for atmospheric N₂O and larger emission flux with a range from 0.125 mg N₂O.m^-2.h^-1 to 0.232 mg N₂O.m^-2.h^-1. The N₂O emission flux from lawns in this area had obvious diurnal and seasonal dynamics. There appeared two peaks for N₂O that occurred in middle May and late July and appeared holistic variation character of "higher-lower-higher-lower" in the whole monitoring period. The temperature had influences on N₂O diurnal variation, and was the key factor for N₂O seasonal dynamics. Soil moisture and biomass of vegetations were proved to be another significant factors for N₂O emission flux.