Grazing changes topography-controlled topsoil properties and their interaction on different spatial scales in a semi-arid grassland of Inner Mongolia, P.R. China
Grazing changes topography-controlled topsoil properties and their interaction on different spatial scales in a semi-arid grassland of Inner Mongolia, P.R. China
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DOI：
10.1007/s11104-010-0473-4
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发表时间：
2011-03-01
期刊：
影响因子：
4.9
通讯作者：
Koegel-Knabner, Ingrid
中科院分区：
文献类型：
--
作者：
Koelbl, Angelika;Steffens, Markus;Koegel-Knabner, Ingrid
半干旱草原生态系统占据了大片陆地面积，被认为是大型碳(C)汇。然而，在不同的空间尺度上，包括地形的影响，表层土壤对放牧敏感性的基本信息缺乏。我们的跨学科方法考虑了土壤化学、物理和植被特性，包括对坑尺度（平方米尺度）、地块尺度（公顷尺度）和景观剖面尺度（几公顷）的调查。五个不同的地点，代表放牧强度梯度，从长期放牧圈地到重度放牧地点。在坑尺度上，对代表性土壤剖面的表层土样品进行了团聚体粒径分布、不同土壤有机碳库数量、有机碳矿化、导水率和抗剪强度等数据分析。在常规正交网格的基础上，通过在样地尺度和景观剖面上使用两种不同网格尺寸，分析了不同放牧处理下地形参数、表层土壤质地、容重、有机碳、疏水性和植被覆盖度的空间变异性。在坑尺度上，集约放牧明显降低了土壤团聚体和新鲜、凋落物样颗粒有机质（POM）的数量。弱聚集与动物践踏相结合，导致有机碳矿化增强，表层土壤容重增加，入渗率降低，随后土壤侵蚀风险增加。在样地尺度上，放牧对土壤结构破坏的影响因植被斑块的退化而增强，导致土壤表面的润湿性受到质地控制。放牧封育区表层土壤由于POM含量较高，具有良好的机械特性和soc控制的润湿性。地质统计学和一般线性模型相结合的方法确定地形是在景观剖面尺度上形成纹理分数和相关土壤参数空间分布的基本因素。放牧强烈干扰地形控制的颗粒迁移过程，对地上生物量产量和与生物量相关的土壤性质（如有机碳储量）的影响最大。我们得出结论，跨学科的多尺度分析是必要的：(1)区分地形和放牧控制的表土和植被特性的空间格局；(2)在小尺度上识别主要的放牧敏感过程，这些过程与大尺度上的空间分布和迁移过程相互作用。
Semiarid steppe ecosystems account for large terrestrial areas and are considered as large carbon (C) sinks. However, fundamental information on topsoil sensitivity to grazing is lacking across different spatial scales including the effects of topography. Our interdisciplinary approach considering soil chemical, physical, and vegetation properties included investigations on pit scale (square-metre scale), plot scale (hectare scale), and the scale of a landscape section (several hectares). Five different sites, representing a grazing intensity gradient, ranging from a long-term grazing exclosure to a heavily grazed site were used. On the pit scale, data about aggregate size distribution, quantity of different soil organic carbon (SOC) pools, SOC mineralisation, hydraulic conductivity and shear strength was available for topsoil samples from representative soil profiles. Spatial variability of topographical parameters, topsoil texture, bulk density, SOC, water repellency, and vegetation cover was analysed on the basis of regular, orthogonal grids in differently grazed treatments by using two different grid sizes on the plot scale and landscape section. On the pit scale, intensive grazing clearly decreased soil aggregation and the amount of fresh, litter-like particulate organic matter (POM). The weak aggregation in combination with animal trampling led to an enhanced mineralisation of SOC, higher topsoil bulk densities, lower infiltration rates, and subsequently to a higher risk of soil erosion. On the plot scale, the effects of soil structure disruption due to grazing are enhanced by the degradation of vegetation patches and resulted in a texture-controlled wettability of the soil surface. In contrast, topsoils of grazing exclosures were characterised by advantageous mechanical topsoil characteristics and SOC-controlled wettability due to higher POM contents. A combined geostatistical and General Linear Model approach identified topography as the fundamental factor creating the spatial distribution of texture fractions and related soil parameters on the scale of a landscape section. Grazing strongly interfered with the topography-controlled particle relocation processes in the landscape and showed strongest effects on the aboveground biomass production and biomass-related soil properties like SOC stocks. We conclude that interdisciplinary multi-scale analyses are essential (i) to differentiate between topography- and grazing-controlled spatial patterns of topsoil and vegetation properties, and (ii) to identify the main grazing-sensitive processes on small scales that are interacting with the spatial distribution and relocation processes on larger scales.