Degradation and small-scale spatial homogenization of topsoils in intensively-grazed steppes of Northern China
Degradation and small-scale spatial homogenization of topsoils in intensively-grazed steppes of Northern China
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DOI：
10.1016/j.still.2009.04.005
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发表时间：
2009-07
影响因子：
6.5
通讯作者：
M. Wiesmeier;M. Steffens;A. Kölbl;I. Kögel‐Knabner
中科院分区：
文献类型：
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作者：
M. Wiesmeier;M. Steffens;A. Kölbl;I. Kögel‐Knabner
在过去的几十年里，过度放牧导致了中国北方半干旱草原的严重退化和荒漠化。尽管半干旱草原植被具有异质性分布，但放牧对土壤性质空间分布的影响却很少引起人们的关注。以内蒙古羊草和大针茅为主的草原生态系统为研究对象，测定了连续放牧（CG）和未放牧（UG79= 1979年围篱和未放牧）2个样地土壤有机碳（SOC）、全氮（Ntot）、全硫（Stot）、体积密度（BD）、pH、Ah厚度和碳同位素比值（δ13C）的空间格局。每个站点的表层土壤（0-4cm）采用一个大网格（120m×150m）和一个小地块（2m×2m），分别有100个采样点和40个采样点。应用地质统计学方法，分别在野外（120m×150m格网）和植物（2m×2m样地）尺度上进行空间分布分析。两个试验点的SOC、Ntot、stot的浓度和储量均显著降低，BD显著升高。在野外尺度上，这些参数的半变异图显示UG79位点的非均匀分布和CG位点的均匀分布，而核基比则显示出较高的小尺度变异性。在植物尺度上，所有研究参数的半方差在UG79位点比CG位点高一个数量级。UG79站点表土性质的异质性可归因于被裸露土壤隔开的植被斑块的马赛克。两种草原类型的自相关范围与草丛和灌木的空间扩展基本一致。在CG站点，羊和蹄对生物量的消耗消除了植被斑块，导致土壤化学和物理性质均质化。研究结果表明，植物尺度（<2m）表土性质的空间分布可以作为半干旱草地退化的一个指标。我们的研究结果进一步表明，在半干旱草地生态系统中，非均质植被和相关表土结构的维持对SOM的积累至关重要。
Overgrazing has led to severe degradation and desertification of semi-arid grasslands in Northern China over the last decades. Despite the fact that vegetation is often heterogeneously distributed in semi-arid steppes, little attention has been drawn to the effect of grazing on the spatial distribution of soil properties. We determined the spatial pattern of soil organic carbon (SOC), total nitrogen (Ntot), total sulphur (Stot), bulk density (BD), pH, Ah thickness, and carbon isotope ratios (δ13C) at two continuously grazed (CG) and two ungrazed (UG79=fenced and excluded from grazing in 1979) sites in Leymus chinensis and Stipa grandis dominated steppe ecosystems in Inner Mongolia, Northern China. Topsoils (0–4cm) were sampled at each site using a large grid (120m×150m) with 100 sampling points and a small plot (2m×2m) with 40 points. Geostatistics were applied to elucidate the spatial distribution both at field (120m×150m grid) and plant (2m×2m plot) scale. Concentrations and stocks of SOC, Ntot, Stotwere significantly lower and BD significantly higher at both CG sites. At the field scale, semivariograms of these parameters showed a heterogeneous distribution at UG79 sites and a more homogeneous distribution at CG sites, whereas nugget to sill ratios indicated a high small-scale variability. At the plant scale, semivariances of all investigated parameters were one order of magnitude higher at UG79 sites than at CG sites. The heterogeneous pattern of topsoil properties at UG79 sites can be attributed to a mosaic of vegetation patches separated by bare soil. Ranges of autocorrelation were almost congruent with spatial expansions of grass tussocks and shrubs at both steppe types. At CG sites, consumption of biomass by sheep and hoof action removed vegetation patches and led to a homogenization of chemical and physical soil properties. We propose that the spatial distribution of topsoil properties at the plant scale (<2m) could be used as an indicator for degradation in semi-arid grasslands. Our results further show that the maintenance of heterogeneous vegetation and associated topsoil structures is essential for the accumulation of SOM in semi-arid grassland ecosystems.