Study On The Greenhouse-gas Emission And Characteristics Of Soil Microbe On Dry Land Agro-ecology System In Chengdu Plain

This paper dealt with the flux seasonal variation rule of nitrous dioxide and carbon dioxide by static chamber-gas chromatographic techniques in the dry-land agro-ecology in Chengdu plain. There were three kind of treatments: (1)treatment with urea(N_U), (2) treatment without urea(N_O), (3)treatment without crop(N_P). Three types of soil enzyme activity and microbial biomass(C,N) were determined, furthermore the gene diversity were analyzed by the denaturing gradient gel electrophoresis (DGGE). To reveal the relationship between N₂O,CO₂ emission fluxes and soil microbial activities, the results were reported as follows:1) The nitrous dioxide and the carbon dioxide emission fluxes had a seasonal fluctuation which related to the change of temperature. The range of N₂O emission flux in rape and wheat fields was 0.01～0.48 mg m^-2h^-1 and 0.02～0.24 mg m^-2h^-1; And the range of CO₂ emission flux was 121.42～1585.80 mg·m^-2·h^-1 and 142.39～1246.19 mg·m^-2·h^-1, respectively. The emission fluxes were at a low level and had no obviously change during the early days after the semination of wheat and transplant of rape. Following the rise of temperature in the next year,the soil N₂O,CO₂ emission fluxes kept increasing, and got to the highest value when the crops were in its florescence. During the maturity period the emission fluxes decreased to a low level.2) During the crop growth period, N₂O,CO₂ emission fluxes were positively correlated with the soil temperature at 5 cm depth but negatively correlated with the soil moisture(R=-0.478^**), and the correlations were significant at 0.01 level. N₂O,CO₂ emission fluxes were higher in the treatment N_U than those in the treatment No, which showed that fertilization improved the soil N₂O,CO₂ emission fluxes. N₂O,CO₂ emission fluxes in all the treatments of rape field were higher than those in the corresponded treatments of wheat field.3) Results of edaphon diversity by DGGE analysis of soil DNA showed that both bacteria and fungi Shannon index of treatment N_U were lower than those of treatment No, which suggested that planting crop decreased the soil microbial Shannon index. However there was no difference between the same treatments in rape and wheat fields.4) The micrbial biomass C in the treatment N_U was higher than that in the treatment N_p. The micro biomass N in all the treatments in rape field was higher than that in the corresponding treatments in wheat field. The order of microbial biomass N in both rape and wheat fields was as following: N_P＞N_U＞N_O and which demonstrated the microbial biomass N was related with the N level in soil.5) The soil enzyme activities were different in the two types of plantations and the activity of catalase and invertase in rape and wheat fields changed as following: N_U＞N_O＞N_P; Soil catalase activity in all treatments in rape field was higher than that in the corresponding treatments in wheat field. However the soil invertase activity between rape and wheat fields was at the same level, which showed that the plant did little influence to soil invertase activity. Soil urease activity in treatments N_U and N_P was higher than that in treatment N_O, so the use of urea improved soil urease activity.