生物土壤结皮对风沙土和黄绵土膨胀特性的影响

作为重要的土壤物理性质，膨胀性在影响土壤导水性、持水性、抗蚀性以及土壤结构的形成和发育等方面发挥着重要作用。为了探讨生物土壤结皮（BSCs）土壤的膨胀特性及其主要影响因素，针对黄土高原风沙土和黄绵土两种典型土壤，利用膨胀仪测定并比较了有、无藓结皮及其在不同因素（初始含水量、干湿循环、冻融循环、温度）下膨胀率的差异，分析了BSCs对土壤膨胀性的影响及其与环境因素和BSCs性质的关系。结果显示：风沙土上藓结皮的膨胀率为1.93%，较无结皮增加了8.65倍；而黄绵土上藓结皮的膨胀率为2.05%，与无结皮相比降低了76.68%。藓结皮的生物量和厚度与其膨胀率在风沙土上均呈线性正相关关系（P < 0.05），在黄绵土上分别呈二次函数（P=0.02）和线性正相关关系（P=0.02）。初始含水量同时影响了土壤最大膨胀率和稳定膨胀时间，影响程度风沙土远大于黄绵土（包括藓结皮和无结皮）；干湿循环次数对无结皮土壤膨胀率的影响程度大于藓结皮土壤，其中风沙土和黄绵土上无结皮的膨胀率分别是50.00%~620.00%和-2.28%~10.81%，而两种土壤上藓结皮的膨胀率分别是-5.70%~10.88%和-10.24%~-21.46%；冻融循环下4种土壤的膨胀率均有不同程度的降低，降幅为0~18.54%。黄绵土无结皮的膨胀率受温度影响程度较大，50℃下黄绵土无结皮的膨胀率分别是25℃和35℃下的1.17倍和1.21倍。BSCs显著地改变了风沙土和黄绵土表层的膨胀性，其影响的程度和方向取决于土壤类型。同时，BSCs的膨胀性受含水量、温度、干湿以及冻融循环等关键因素影响。

Effects of moss-dominated biocrusts on the swelling characteristics of aeolian and loessal soil in the Chinese Loess Plateau

As one of the important physical properties of soil, swelling characteristic plays an important role in affecting the water conductivity, water holding capacity, corrosion resistance of soil and the formation and development of soil structure. In order to investigate the swelling characteristics and influencing factors of biocrusts, we took moss-dominated biocrusts and bare soil from aeolian and loessal soil on the Loess Plateau, and investigated their differences in swelling rates under different factors (initial water content, dry-wet cycle, freeze-thaw cycle, temperature) using soil dilatometer. The relationships between the swelling rates of the samples and the environmental factors or biocrusts properties were also analyzed. The results showed that the swelling rate of aeolian soil with biocrusts was 1.93%, which was 8.65 times higher than that without crust; the swelling rate of the loessal soil with biocrusts was 2.05%, which was 76.68% lower than the loessal soil without crust. At the same time, the biomass and thickness of biocrusts on aeolian soil were linearly positively correlated with the swelling rate (P < 0.05), and they were quadratic functions (P=0.02) and positive correlations on the loessal soil (P=0.02), respectively. The initial water content also affected the maximum swelling rate and stable swelling time, and the degree of influence was that the aeolian soil was much larger than the loessal soil (including the biocrusts and bare crust); The degree of dry-wet cycle numbers affected the swelling rate of bare soil more than that of biocrusts. The dry-wet cycle changed the swelling rate of bare soil on aeolian soil and loessal soil from 50.00% to 620.00% and from -2.28% to 10.81%, respectively; and the swelling rate of the biocrusts on both soils changed from -5.70% to 10.88% and from -10.24% to -21.46%, respectively. Under the freeze-thaw cycle, the swelling rates of four soils decreased to varying degrees, with a decrease of 0 to 18.54%. The swelling rate of the loessal soil without crust was greatly affected by the temperature, and the swelling rate of loessal soil without crust at 50℃ was 1.17 and 1.21 times at 25℃ and 35℃, respectively. The studies have shown that the biocrusts significantly changed the swelling of the surface soil of aeolian soil and loessal, but the extent and direction of its impact depended on the soil type. At the same time, the swelling of biocrusts is affected by several key factors such as water content, temperature, wet and dry, and freeze-thaw cycles.