干旱区生态环境知识资源中心

In a global meta study, which contained 157 biological soil crust (BSC) samples from all climatic regions worldwide, climatic and soil texture threshold values favoring BSC development were derived. Response variable was the "relative crust biomass", which was computed per literature source as the ratio between each individual crust biomass value of the given study to the study maximum value reported. Four crust types were distinguished: cyanobacterial, lichen, green algal and moss crusts. To quantify threshold conditions at which crust biomass responded to differences in texture and climate, we (I) determined correlations between bioclimatic variables, (II) calculated generalized linear models to determine the effect of typical climatic variables with soil clay content and with study site as a random effect. (III) Thresholds of climatic and texture effects were identified using a regression tree. Three mean annual temperature classes for texture dependent BSC growth limitation were identified: (1) < 9 degrees C with a threshold value of 25% silt and clay (limited growth on coarser soils), (2) 9-19 degrees C, where texture did have no influence on relative crust biomass, and (3) > 19 degrees C at soils with < 4 or > 17% silt and clay. Non of the precipitation related bioclimatic variables did influence the relative crust biomass significantly. Because biocrust development is limited under certain climatic and soil texture conditions, it is suggested to consider soil texture in biogeochemical modeling of cryptogamic ground covers.