宁夏东部荒漠草原向灌丛地人为转变过程土壤粒径分形特征

Changes in soil particle size distribution and fractal characteristics across an anthropogenic transition from desert steppe grassland to shrubland in eastern Ningxia

以宁夏东部荒漠草原-人工灌丛地典型镶嵌区域为研究对象,根据生态界面理论,选取荒漠草地、草地边缘、灌丛边缘、灌丛地为主要转变样地,利用野外采样室内分析的方法,研究荒漠草原向灌丛地人为转变过程土壤性状、土壤粒径分形维数变化特征及其相互关系。结果表明,转变过程各样地土壤颗粒体积百分含量均表现为砂粒>粉粒>黏粒,且砂粒比例随着过渡逐渐增加,灌丛地最高,达98.97%;土壤分形维数变化介于1.02~2.58,随着转变过程呈降低趋势,抗土壤侵蚀能力逐渐降低,其中荒漠草地、草地边缘、灌丛边缘间无显著差异(P>0.05),但均显著高于灌丛地36.79%~41.48%(P<0.05)。土壤分形维数变化在转变过程中与黏粒含量(<2μm)、粉粒含量(2~50μm)呈显著正相关关系(P<0.05),与砂粒含量(50~2000μm)呈显著负相关关系(P<0.05);与土壤水分含量、毛管孔隙度、有机碳含量、全磷含量呈极显著或显著正相关关系(P<0.01,P<0.05),与土壤容重呈极显著负相关关系(P<0.01)。主成分分析表明,土壤粉粒、土壤砂粒、土壤毛管孔隙度、土壤容重、土壤有机碳,土壤全磷在草地向灌丛地人为转变过程中对土壤粒径分形维数影响较大(P<0.05)。

This research aimed to characterize changes in soil particle size and fractal dimensions across a grassland-shrubland vegetation transition boundary in the desert steppe of Eastern Ningxia.Following ecological boundary theory and standard methodology,sites located in desert grassland,at the grassland edge,at the shrubland edge,and in shrubland were selected as representative of the main states found in a typical anthropogenic grassland-shrubland transition in vegetation mosaics in the region.Samples were collected for 0-10 cm,10-20 cm and thereafter 20 cm soil depth increments to 100 cm.It was found that the percentage of soil volume by particle size in the transition zone studied was sand>silt>clay.The proportion of sand increased gradually across the anthropogenic transition from approximately 70%in grassland to 95.54%-98.97%in the shrubland,depending on soil depth.Conversely,soil fractal dimension decreased with increasing sand content from 2.10-2.42 in desert grassland to 1.02-1.78 in shrubland.Soil fractal dimension did not differ significantly between desert grassland,grassland edge and shrubland edge(P>0.05),but the soil fractal dimension at all three of these site categories was significantly higher,by36.79%-41.48%,than in shrubland(P<0.05).The change of soil fractal dimension across the vegetation transition zone was significantly positively correlated with clay content(<2μm)and silt particle content(2-50μm),but significantly negatively correlated with sand content(50-2000μm).The soil fractal dimension also showed a very significant positive correlation with soil moisture content,capillary porosity,organic carbon content,and soil total phosphorus(P<0.01,P<0.05),and a significant negative correlation with soil bulk density(P<0.01).A principal component analysis indicated that soil silt and sand content,soil capillary porosity,soil bulk density,and soil organic carbon and total phosphorus contents were the parameters most closely associated(P<0.05)with the change in soil fractal dimension across the studied anthropogenic vegetation community transition.