大田原位条件下,种植元阳梯田地方水稻品种白脚老粳,研究UV-B辐射增强(0、5.0 k J·m-2)对水稻生长期稻田土壤活性有机碳含量及其转化相关酶活性、温室气体排放量的影响,结果表明:UV-B辐射增强导致稻田土壤多酚氧化酶和蔗糖酶的活...大田原位条件下,种植元阳梯田地方水稻品种白脚老粳,研究UV-B辐射增强(0、5.0 k J·m-2)对水稻生长期稻田土壤活性有机碳含量及其转化相关酶活性、温室气体排放量的影响,结果表明:UV-B辐射增强导致稻田土壤多酚氧化酶和蔗糖酶的活性显著降低,降幅为10%~17%;纤维素酶活性分蘖期和拔节期显著增加,分别增加了2.7 U·g^(-1)和5.5 U·g^(-1)。UV-B辐射增强显著降低水稻孕穗期、抽穗期和成熟期稻田土壤微生物量碳和易氧化有机碳的含量,降幅分别为10%~36%和9%~31.5%;增加拔节期、孕穗期和成熟期土壤溶解性有机碳的含量,分别增加了123.0、79.5 mg·kg^(-1)和57.8 mg·kg^(-1)。UV-B辐射增强显著降低水稻生长期稻田CH4的排放通量,降幅为23%~42%;但显著增加CO2和N2O的排放通量,分别平均增加418.9 mg·m-2·h-1和3.7μg·m-2·h-1。相关分析发现,稻田土壤多酚氧化酶活性与微生物量碳、易氧化有机碳含量呈显著正相关,且土壤微生物量碳含量与CH4排放通量呈极显著正相关。因此,UV-B辐射通过改变稻田土壤碳转化酶活性与活性有机碳含量,进而影响稻田温室气体排放。展开更多
Double-electrode gas shielded arc welding （ DE - GMAW） was used to weld the magnesium alloy cylinder with the diameter of 200 mm and the thickness of 6 mm. In order to study the residual stress distribution of AZ31B...Double-electrode gas shielded arc welding （ DE - GMAW） was used to weld the magnesium alloy cylinder with the diameter of 200 mm and the thickness of 6 mm. In order to study the residual stress distribution of AZ31B magnesiunl alloy welding point, numerical sinmlation of welding temperature field, stress field and residual stress were carried out by MSC. mare software. The results show that the residual stress in the weld and the heat affected zone is large, and with the increase of the distance away from the weld center, the residual stress decreases. In most areas, the longitudinal residual stress is greater than the transverse residual stress （except for the inside and outside surfaces of the weld） , all of which provides theoretical support for the study of magnesiunl alloy welding residual stress.展开更多
文摘Double-electrode gas shielded arc welding （ DE - GMAW） was used to weld the magnesium alloy cylinder with the diameter of 200 mm and the thickness of 6 mm. In order to study the residual stress distribution of AZ31B magnesiunl alloy welding point, numerical sinmlation of welding temperature field, stress field and residual stress were carried out by MSC. mare software. The results show that the residual stress in the weld and the heat affected zone is large, and with the increase of the distance away from the weld center, the residual stress decreases. In most areas, the longitudinal residual stress is greater than the transverse residual stress （except for the inside and outside surfaces of the weld） , all of which provides theoretical support for the study of magnesiunl alloy welding residual stress.
