|其他摘要||The effects of farmland managements on soil CO2 emissions have become one of the important part of the global carbon cycle and global warming researches. If the effects of farmland managements on farmland soil carbon library measure by long time and accurate measurements would provide prerequisite and foundation of assessing the function of terrestrial ecosystem in carbon source and carbon sink and predicting response of ecosystem to climate change. This study was conducted at Aksu station in Xinjiang，and oasis cotton soil was selected as the subject in this thesis. To carry out the effect of different cotton straw returned ways on decomposition, and the spatial and temporal distribution characteristic of soil CO2 under cotton straw returned, and drying-wetting alteration (caused by irrigating) and straw and nitrogen application on soil CO2 emissions, the main results were listed as follows:
1 To study the effects of different cotton straw returned ways on decomposition rates, using the nylon mesh bags method, we found that: 1) The decomposition rate of cotton straw returned was faster at the initial stage decomposition but then slowed down right through the final stage of decomposition. 2) There was no significant effects of cotton straw returned amounts on decomposition rates (P>0.05). 3) After 90d’s straw returned, the less length of cotton straw was beneficial to decompose. But then, there was no significant effect cotton straw returned of length on decomposition rates (P>0.05). 4) The effects of different depths of cotton straw returned on decomposition rates showed that the decomposition ratios of surface was minimum, the depth of 10cm was mediate, and the depth of 20cm was maximum.
2 The spatial and temporal distributions of soil CO2 concentration and efflux under cotton straw returned were conducted by using closed chamber method and diffusion chamber technique in oasis arid areas. The soil CO2 concentration and efflux of temporal variations exhibited similar pattern, with a peak in July and a minimum in October, but compared to NS (control), soil CO2 concentration and efflux also reached a peak in May under cotton straw returned. The vertical distributions of soil CO2 concentration were increased with the increase of soil depth, but no significant effect on soil CO2 concentration of vertical distribution under cotton straw returned. Inherence, cotton straw returned played an important role in soil CO2 concentration and efflux under different treatments, and soil CO2 concentration and efflux were significantly higher in double amounts of cotton straw returned than other treatments (P<0.05). In addition, the soil CO2 concentration and efflux were significant correlation (P < 0.05), which increased with the amounts of cotton straw returned, indicating that the soil CO2 efflux strongly depends on the soil CO2 concentration.
3 To evaluate the effects of soil moisture content and drying and wetting alternation on soil CO2 emissions were carried out in laboratory incubation. The results showed that: 1) Compared with 60% WFPS (water filling soil porosity), 40% WFPS was inhibitory on soil CO2 emissions (P<0.05), while 80% WFPS existed no significant influence on soil CO2 emissions (P>0.05). 2) After alternation cycles of many times, the soil CO2 accumulative emissions were lower than constant moisture treatment (P<0.05). Under different drought intensity, severe drought was higher than moderate drought for the effects of range of on soil CO2 emission rate, but after many times, severe drought was lower than moderate drought for the accumulation of soil CO2 emissions. As the times of drying and wetting alternation increased, the soil CO2 emission rates were reduced significantly, especially for the maximum of soil CO2 emission rate.
4 According to the effects of straw and nitrogenous fertilizer on soil CO2 emissions in an incubation, we found that: 1) Cotton straw returned significant increased soil CO2 emissions and soil organic carbon (P<0.05), but applying nitrogenous fertilizer had no significant effects on soil CO2 emissions and soil organic carbon (P > 0.05). 2) In the form of CO2 emissions of carbon accounts for percentage total carbon of straw decomposed, the maximum were 48.71 and 50.72% under moderate straw and Low nitrogen level, and the minimum were 46.68 and 45.94% under double straw+ no fertilizer level. 3）The effect of amount of cotton straw returned and nitrogen application on EF(emission factor of straw carbon), the maximum of emission factor of straw carbon were 36.68 and 35.71 under moderate straw and no fertilizer level, and the minimum of EF were 33.53 and 34.86% under double straw and high nitrogen level, but EF was not a constant under different treatments.|