不同利用方式对小针茅荒漠草原土壤有机碳储量及其结构的影响

在围封、3个放牧梯度[0.50羊单位·hm~(-2)(G0.50)、0.94羊单位·hm~(-2)(G0.94)、1.25羊单位·hm~(-2)(G1.25)]和开垦5种处理条件下,对内蒙古小针茅荒漠草原土壤容重、土壤有机碳含量、有机碳密度和有机碳储量的影响开展野外监测试验,并利用核磁共振波谱法测定0~20 cm土层土壤有机碳结构。结果表明:同一土层,不同利用方式下,放牧区和开垦区与围封区相比,土壤有机碳含量、有机碳密度有降低的趋势,土壤容重有增加的趋势。随着放牧强度的增加,土壤有机碳含量、有机碳密度表现为逐渐降低的趋势。同一处理,随着土层的加深,小针茅荒漠草原土壤容重先降低后增加,而土壤有机碳含量和有机碳密度先增加后降低,在30~40 cm土层达到最大值。放牧和开垦与围封相比,土壤有机碳储量下降。其中,G1.25和开垦区的土壤有机碳储量显著(P0.05)低于围封区。随着放牧强度的增加,土壤有机碳储量逐渐降低。不同利用方式和放牧强度下小针茅荒漠草原土壤有机碳化学组分没有发生变化,各组分的相对比例出现差异。其中,烷氧碳(34.86%~37.85%)、烷基碳(26.05%~33.87%)、芳香碳(10.60%~17.69%)和羰基碳(14.57%~16.90%)是土壤有机碳结构的主要组成成分。放牧区和开垦区与围封区相比,烷基碳和羰基碳的相对比例减小,烷氧碳和芳香碳的相对比例增加,随着放牧强度的增加,烷基碳的相对比例逐渐降低,烷氧碳相对比例逐渐增加。围封草原土壤腐殖化指数最大(表现为围封区开垦区G0.50G0.94G1.25),而芳香性最小(表现为G1.25G0.94开垦区G0.50围封区),说明围封区土壤有机碳更趋稳定,在土壤固碳方面有一定的意义。

Effects of different land use types on storage and structure of soil organic carbon in Stipa klemenaii steppe in Inner Mongolia

The composition and structure of soil organic carbon(SOC) are complex and includes many functional components. In order to study the influence of different land use types on SOC storage and structural characteristics in Stipa klemenaii desert steppe of Inner Mongolia, field sampling, laboratory analysis and ¹³C Nuclear Magnetic Resonance(¹³C NMR) were employed to analyze the soil bulk density, SOC content, density and storage in soil depth of 0~100 cm, and the structure of SOC in soil depth of 0~20 cm. 5 different treatments were set up, including three grazing treatments[0.50 sheep·hm^-2(G0.50), 0.94 sheep·hm^-2(G0.94), 1.25 sheep·hm^-2(G1.25)], one enclosure and one reclamation treatments. The enclosed area was fenced excluding livestock and human disturbance while the reclamation area planted maize(Zea mays) as local general agricultural management. The results showed that:compared with the enclosed area, in the same soil layer, SOC content and density showed a decrease trend; soil bulk density showed an increase trend. With the increase of grazing intensity, SOC content and density reduces gradually. In the same treatment, the soil bulk density of S. klemenaii desert grassland firstly reduced then increased as the soil layer deepen, while the content of SOC and SOC density increased then decreased, and reached the maximum in 30~40 cm. Compared with the enclosed area, the SOC declines in the grazing and reclamation areas. In which, the SOC of the G1.25 and reclamation treatments were significantly(P<0.05) lower than the enclosed area, besides, the SOC reduce gradually with the increase of grazing intensity. The influence of different land use types on S. klemenaii desert grassland SOC structure was mainly embodied on chemicals composition, meanwhile the chemicals of SOC component has not changed. Of which, silane oxygen carbon(34.86%~37.85%), alkyl carbon(26.05%~33.87%), aromatic carbon(10.60%~17.69%) and carbonyl carbon(14.57%~16.90%) are the main compositions of SOC structure. Compared with grazing and reclamation, the soil humification index of the enclosure grassland was the biggest, which performed as enclosed area>reclamation area >G0.50 >G0.94 >G1.25; however the aromatic degree of enclosure grassland was the smallest, characterized by G1.25 >G0.94 >reclamation area >G0.50 >enclosed area. Which demonstrated that the SOC in enclosed area was more stable, and had certain significance in terms of soil carbon sequestration.