不同尺度苔藓结皮土壤性状的空间分布特征

Abstract

Biological soil crusts are the organic complexes composed of bacteria,cyanobacteria,algae,lichen and moss with soil particles. They play critical roles in desert ecosystems,including enhancing soil stability and fertility,preventing soil erosion by water or wind,facilitating seed germination. Moss crust is the latest successional stage of biological soil crusts in arid and semiarid land,which perform important functions. Most of the studies focused on the difference of soil properties between moss crust and lack of moss crust. Generally,moss crust distributes in patches in interdune areas of sand dunes,it is a small scale. Little is known about its nutrients distribution at patch scale. The aims of this research are to( 1) make sure the strength of soil heterogeneity for moss crust at both quadrate scale and patch scale;( 2) support basic data for moss crust according to patch size. In this study,patch' s area is calculated by Photoshop CS 5. 0. Five soil physiochemical properties were analyzed with standard soil analytical methods. Classical statistics,geostatistic techniques,semivariogram model fitting and mapping methods were used to describe the spatial distribution of soil properties at both scales. The results indicated that there were medium variations for five soil properties of moss crusts at both scales.Coefficient variations of five properties at quadrate scale varied from 12% to 30%. With the exception of total phosphorus,most coefficient valuations of the other four properties at patch scale were less than 20%,which indicated the soil spatial heterogeneity of moss crust at quadrate scale is much stronger than that at patch scale. The spatial autocorrelation of five soil properties at quadrate scale ranged from 65% to 92%. For patch scale, except for total phosphorous, spatialautocorrelations of the other four parameters were over 90%,which means,that the proportion of spatial autocorrelations of moss crust increase with the decreasing of sampling scale. Additionally,the effect of structure factors increased on patch scale with the decreasing proportion of the random factors,which was consistent with the result of spatial autocorrelation. In this study,values of soil water,organic matter and total nitrogen decreased from center of moss patch to edge,however,total phosphorus increased from center to edge at patch scale,which indicated that there was heterogeneity for moss crust patch at micro scale. There was irregular change for total soluble salt at patch scale,but at quadrate scale,total soluble salt content with mosses was much higher than that without mosses,which implied that with the decreasing of sampling scale,the heterogeneity of soil salt disappeared. The autocorrelation ranges of water,organic,total nitrogen and total phosphorus at patch scale were smaller than the diameter of the moss crusts patch,autocorrelation range of total soluble salt was out of patch size,on the whole,autocorrelation ranges in creased with the sampling size. Thus,sampling distance can be increased at quadrate scale, but for patch scale, sampling distance should be reduced to avoid missing the tiny heterogeneity. At both scales,the lowest autocorrelation range of total phosphorus was observed. Therefore,the sampling distance must be short for variation of phosphorus,while for total salt,sampling distance can be increased properly due to its big variation range.