基于地统计学的退化草地狼毒种群土壤种子库空间异质性

Spatial heterogeneity analysis of soil seed bank for degraded grassland Stellera chamaejasme populations based on geostatistics

土壤种子库作为植被天然更新的物质基础,其空间异质性对于认识种群繁殖更新机制具有重要意义。利用野外调查和地统计学方法,设置4个草地退化梯度,研究了祁连山北坡狼毒种群土壤种子库空间异质性及其与地上植被的关系。结果表明：4个退化梯度草地土壤种子库的半变异函数模型均为非线性模型,表现为聚集分布;随着天然草地退化程度加剧,狼毒种群土壤种子库的密度与变程不断增大、基台值与结构比呈＂U＂型变化趋势,其中76.88%-93.75%的空间异质性是由空间自相关引起;在未退化和重度退化草地地上植被密度与土壤种子库密度呈正相关,在轻度和中度退化草地中地上植被密度与土壤种子库密度之间未呈现相关性。在草地退化演替过程中,土壤种子库空间分布主要受地上植被等结构性因素影响,而放牧等干扰因素也在一定程度上降低了空间自相关性。

Soil seed bank is the material basis for natural regeneration of vegetation; the spatial heterogeneity of soil seed bank is of important significance for understanding the mechanism of population reproduction and regeneration. Based on field survey and geostatistics method, this pa- per studied the spatial heterogeneity of soil seed bank in four differently-degraded grasslands and its relationship with the ground vegetation of Stellera chamaejasme population in the northern slope of Qilian Mountains, Northwest China. Our results showed that the semivariogram models of soil seed bank in the four degraded grassland gradients were nonlinear, showing aggregated distribu- tion. With the aggravation of grassland degradation, the density and range of soil seed bank in- creased, the sill and structure proportion showed the trend of ＂U＂ type, and the spatial heteroge- neity of 76.88%-93.75% was caused by the spatial autoeorrelation. Furthermore, in both the no- degradation and heavy-degradation grasslands, the relationship between ground vegetation density and seed bank density of S. chamaejasme population showed a significant positive correlation; in factors such as ground vegetation, while grazing and other disturbance factors to a certain extent reduced the spatial autocorrelation.