草地修复是推动草地生态系统恢复和实现可持续发展的关键。为了探究翻耕和植物残体覆盖对极度退化高寒草地土壤氧化亚氮(N_(2)O)排放的影响,以青藏高原东缘高寒草甸为研究对象,设置了移除草地地上和地下(0~20cm)全部植物以模拟“黑土滩...草地修复是推动草地生态系统恢复和实现可持续发展的关键。为了探究翻耕和植物残体覆盖对极度退化高寒草地土壤氧化亚氮(N_(2)O)排放的影响,以青藏高原东缘高寒草甸为研究对象,设置了移除草地地上和地下(0~20cm)全部植物以模拟“黑土滩”型退化草地(CK)、退化草地进行翻耕(PL)、退化草地进行植物残体覆盖(MR)、退化草地进行翻耕和植物残体覆盖(PL+MR)4种处理,并测定不同处理下的土壤基础理化指标、微生物生物量、胞外酶活性、硝化和反硝化酶活性、功能微生物基因丰度和28 d N_(2)O累积排放量。结果显示:翻耕较对照显著增加了土壤N_(2)O累积排放量,增加了44.2%,翻耕后进行植物残体覆盖显著抑制了N_(2)O排放,减少了29.1%。翻耕后,土壤pH、可溶性有机碳(DOC)和微生物生物量碳(MBC)含量、β-1,4-葡萄糖苷酶(BG)和β-1,4-N-乙酰氨基葡萄糖苷酶(NAG)活性、氨氧化古菌(AOA)和氨氧化细菌(AOB)amoA基因丰度显著增大,增幅分别为2.6%、209.5%、23.8%、180.4%、233.9%、74.6%和68.0%,土壤C/N、有机碳(SOC)和微生物生物量氮(MBN)含量显著降低,降幅分别为11.3%、13.6%和72.8%。翻耕后覆盖植物残体较翻耕显著降低了土壤DOC含量,抑制了BG、NAG、亮氨酸氨基肽酶(LAP)、酸性磷酸酶(AP)活性及AOA-amoA、AOB-amoA和nosZⅠ基因丰度,降幅分别为12.8%、49.1%、59.9%、31.6%、25.0%、46.5%、59.5%、23.1%,显著增加了MBN含量,增幅为29.1%。相关性分析表明,土壤N_(2)O累积排放量与pH、DOC含量、胞外酶活性、氮循环基因丰度(除nirS以外)均呈显著正相关,而与C/N、SOC和MBN含量显著负相关。AOA-amoA和AOB-amoA丰度是影响N_(2)O排放的关键因子。综上,翻耕会增加土壤胞外酶活性和amoA基因丰度,但会导致SOC分解消耗和N_(2)O增排,而植物残体覆盖能够有效缓解这些负面影响,是一种可行的改良措施。展开更多
Assuming linear theory, the two-dimensional problem of water wave scattering by a horizontal nearly circular cylinder submerged in infinitely deep water with an ice cover modeled as a thin-elastic plate floating on wa...Assuming linear theory, the two-dimensional problem of water wave scattering by a horizontal nearly circular cylinder submerged in infinitely deep water with an ice cover modeled as a thin-elastic plate floating on water, is investigated here. The cross-section of the nearly circular cylinder is taken as r=a（1＋δC（θ））, where a is the radius of the corresponding circular cross-section of the cylinder, δ is a measure of small departure of the cross-section of the cylinder from its circularity and C（θ） is the shape function. Using a simplified perturbation technique the problem is reduced to two independent boundary value problems up to first order in δ. The first one corresponds to water wave scattering by a circular cylinder submerged in water with an ice-cover, while the second problem describes wave radiation by a submerged circular cylinder and involves first order correction to the reflection and transmission coefficients. The corrections are obtained in terms of integrals involving the shape function. Assuming a general Fourier expansion of the shape function, these corrections are evaluated approximately. It is well known that normally incident wave trains experience no reflection by a circular cylinder submerged in infinitely deep water with an ice cover. It is shown here that the reflection coefficient also vanishes up to first order for some particular choice of the shape function representing a nearly circular cylinder. For these cases, full transmission occurs, only change is in its phase which is depicted graphically against the wave number in a number of figures and appropriate conclusions are drawn.展开更多
文摘草地修复是推动草地生态系统恢复和实现可持续发展的关键。为了探究翻耕和植物残体覆盖对极度退化高寒草地土壤氧化亚氮(N_(2)O)排放的影响,以青藏高原东缘高寒草甸为研究对象,设置了移除草地地上和地下(0~20cm)全部植物以模拟“黑土滩”型退化草地(CK)、退化草地进行翻耕(PL)、退化草地进行植物残体覆盖(MR)、退化草地进行翻耕和植物残体覆盖(PL+MR)4种处理,并测定不同处理下的土壤基础理化指标、微生物生物量、胞外酶活性、硝化和反硝化酶活性、功能微生物基因丰度和28 d N_(2)O累积排放量。结果显示:翻耕较对照显著增加了土壤N_(2)O累积排放量,增加了44.2%,翻耕后进行植物残体覆盖显著抑制了N_(2)O排放,减少了29.1%。翻耕后,土壤pH、可溶性有机碳(DOC)和微生物生物量碳(MBC)含量、β-1,4-葡萄糖苷酶(BG)和β-1,4-N-乙酰氨基葡萄糖苷酶(NAG)活性、氨氧化古菌(AOA)和氨氧化细菌(AOB)amoA基因丰度显著增大,增幅分别为2.6%、209.5%、23.8%、180.4%、233.9%、74.6%和68.0%,土壤C/N、有机碳(SOC)和微生物生物量氮(MBN)含量显著降低,降幅分别为11.3%、13.6%和72.8%。翻耕后覆盖植物残体较翻耕显著降低了土壤DOC含量,抑制了BG、NAG、亮氨酸氨基肽酶(LAP)、酸性磷酸酶(AP)活性及AOA-amoA、AOB-amoA和nosZⅠ基因丰度,降幅分别为12.8%、49.1%、59.9%、31.6%、25.0%、46.5%、59.5%、23.1%,显著增加了MBN含量,增幅为29.1%。相关性分析表明,土壤N_(2)O累积排放量与pH、DOC含量、胞外酶活性、氮循环基因丰度(除nirS以外)均呈显著正相关,而与C/N、SOC和MBN含量显著负相关。AOA-amoA和AOB-amoA丰度是影响N_(2)O排放的关键因子。综上,翻耕会增加土壤胞外酶活性和amoA基因丰度,但会导致SOC分解消耗和N_(2)O增排,而植物残体覆盖能够有效缓解这些负面影响,是一种可行的改良措施。
基金the financial support from CTS Visitors Program, Indian Institute of Technology, Kharagpur during the tenure of which the revision of the paper has been made
文摘Assuming linear theory, the two-dimensional problem of water wave scattering by a horizontal nearly circular cylinder submerged in infinitely deep water with an ice cover modeled as a thin-elastic plate floating on water, is investigated here. The cross-section of the nearly circular cylinder is taken as r=a（1＋δC（θ））, where a is the radius of the corresponding circular cross-section of the cylinder, δ is a measure of small departure of the cross-section of the cylinder from its circularity and C（θ） is the shape function. Using a simplified perturbation technique the problem is reduced to two independent boundary value problems up to first order in δ. The first one corresponds to water wave scattering by a circular cylinder submerged in water with an ice-cover, while the second problem describes wave radiation by a submerged circular cylinder and involves first order correction to the reflection and transmission coefficients. The corrections are obtained in terms of integrals involving the shape function. Assuming a general Fourier expansion of the shape function, these corrections are evaluated approximately. It is well known that normally incident wave trains experience no reflection by a circular cylinder submerged in infinitely deep water with an ice cover. It is shown here that the reflection coefficient also vanishes up to first order for some particular choice of the shape function representing a nearly circular cylinder. For these cases, full transmission occurs, only change is in its phase which is depicted graphically against the wave number in a number of figures and appropriate conclusions are drawn.
