放牧对黄河低阶地盐化草场土壤水盐空间异质性的影响

选定黄河低阶地地形大致相近的放牧草场与封育草场,按实地情况分别设置长770m（放牧）、370m（放牧）和240m（封育）3条样线,采用校正后的便携式WET Sensor以10m为间隔进行土壤水盐的分层（0～10cm,10～20cm）测定,并对其进行地统计学分析.结果表明：黄河低阶地盐化草场表层土壤水盐的变异系数和相关性高于下层,土壤水分的变异系数低于土壤盐分且层间的相关性较高;放牧使土壤水盐之间的相关程度增大,变异降低,且使土壤水分存在一定的冗余.所研究草场的土壤水盐表现为中等或强烈空间自相关,封育盐化草场水盐空间相关尺度的差异较小,而放牧草场则相反.持续放牧已经成为一种稳定影响盐化草场水盐空间分布的结构性因素,使盐化草场的水盐空间异质性减弱.盐生植物在草场内随机分布且不受放牧干扰,是封育盐化草场随机作用较强的最可能原因;而放牧草场内牲畜的啃食和践踏对盐生植物和土壤结构改变所形成的反馈作用大大降低了这些植物对水分特别是盐分的再分配,进而导致放牧草场水盐的含量趋于增大且分布格局趋于简单.

Effects of grazing on spatial heterogeneity of soil moisture and salt content in saline grassland in low terrace of the Yellow River

In order to reveal the spatial difference of water and salt in saline grassland under grazing and exclosure,we have chosen three transects(770m,grazing;370m,grazing;240m,exclosure) in two grasslands,which have similar topography in the low terrace of the Yellow River in Inner Mongolia Autonomous Region.Soil moisture and conductivity were sampled at 10 meter intervals along each transect by a portable WET Sensor for two soil layers(0-10cm,10-20cm).And in each soil layer,we got 78,38 and 25 soil moisture and salt content data all severally from three transects.The coefficient of variation(C_v) and the significance of correlation coefficient of the water and salt in surface soil layer were greater than those of the deeper soil layer;the C_v of the water moisture is lower than that of the salt content,but the correlation coefficient is higher in the surface layer.The correlation of the soil moisture and salt content is higher under grazing,and the variance is lower.Spatial autocorrelation of soil water and salt is medium or strong.In the exclosure where the stochastic factor is stronger,the difference of the spatial correlation scale of the soil water and salt is lower.Under grazing,the difference is greater.Continuous grazing is a factor that impacts on the spatial distribution and weakens the spatial heterogeneity of soil moisture and salt content in saline grassland.In the exclosure the distribution of halophytes has a strong effect.While in grazed grassland the distribution of halophytes and soil structure are changed by browsing and trampling of livestock.This has a big impact as both the content of soil water and salt concentration in grazed grassland trends to increase.