生物结皮生长发育对黄绵土抗侵蚀性能的影响

[目的]黄土高原退耕还林(草)工程驱动的生物结皮发育可显著抑制土壤侵蚀,为探明土壤抗侵蚀性能随生物结皮生长发育的变化特征及其响应机制。[方法]设置藻结皮、藓结皮和自然演替结皮3个处理,培育176天,系统研究生物结皮不同发育阶段及其类型差异对黄绵土抗侵蚀性能的影响。[结果](1)生物结皮盖度、厚度、生物量、叶绿素和粗糙度随生长时间均显著增加,培育初期藓结皮较高,培育末期自然演替结皮反而最高。(2)随生物结皮发育,土壤黏结力呈幂函数增强,较初期增加39.8%~60.3%;质量损失率呈指数函数减小,较初期降低45.6%~57.3%;饱和导水率变化趋势较为复杂,但培育末期均最低(0.08~0.12 mm/min)。(3)土壤黏结力随生物结皮盖度、厚度、叶绿素、生物量和表面粗糙度的增加呈幂函数增长,质量损失率随生物结皮盖度、厚度、叶绿素、生物量和表面粗糙度的增加呈指数函数下降。(4)土壤抗侵蚀综合指数(C_(ser))可表示为盖度(Cov)、厚度(T)和生物量(B)的幂函数(Cser=0.279 Cov^(0.194)T^(0.188)B0.119,R^(2)=0.73,p<0.05)。[结论]黄土高原生物结皮发育可显著提高黄绵土抗侵蚀性能,藓结皮效果最强。

草地土壤分离能力季节变化特征及其影响因素

土壤分离能力是土壤侵蚀机理模型的重要参数。受土壤性质、植被根系等因素影响,土壤分离能力呈现显著的季节变化。为研究草地土壤分离能力季节变化特征及其影响机制,以建植一年的柳枝稷、无芒雀麦草地及对照裸地为研究对象,以20 d为周期,测定土壤密度、黏结力和根系密度,并采集原状土样进行水槽实验(τ=6.5-23.4Pa),测量土壤分离能力,并运用相关分析、回归分析等方法,研究土壤性质及植被根系对土壤分离能力季节变化的影响。结果显示:柳枝稷和无芒雀麦草地具有类似的季节变化特征,而裸地与二者差异明显。4月中旬至6月下旬,草地土壤分离能力较大,此后土壤分离能力迅速下降;7月中旬直至10月上旬,草地土壤分离能力较低;10月下旬,土壤分离能力小幅回升;裸地土壤分离能力7、8月份较低,其余时间较高。裸地土壤分离能力试验期均值为柳枝稷草地的10.6倍,无芒雀麦草地的23.7倍。草地土壤分离能力的季节变化受根系密度和土壤黏结力的影响,随着根系密度与土壤黏结力增大,土壤分离能力呈指数形式降低,而土壤密度对土壤分离能力季节变化的影响并不显著。试验区内草地土壤分离能力可用水流剪切力、根系密度、根径和土壤黏结力等参数进行模拟(R2=0.636)。研究结果可为土壤侵蚀机理模型的推广应用,以及小流域水土保持措施配置等工作提供科学依据。

草地土壤细沟可蚀性季节变化研究

[目的]为土壤侵蚀预报模型的校验及中国土壤侵蚀预报机理模型的开发等工作提供科学依据和数据支持。[方法]采用水槽试验方法,研究柳枝稷草地土壤细沟可蚀性的季节变化,在取样同时测量土壤黏结力和根系密度。[结果]草地土壤细沟可蚀性具有明显的季节变化。4月中旬至6月中旬细沟可蚀性较大。此后,土壤细沟可蚀性迅速下降。在7月上旬至9月中旬,细沟可蚀性较低。之后直至生长季末期,细沟可蚀性小幅回升。试验期内草地土壤细沟可蚀性最大值出现在5月下旬,为0.012 s/m,最小值出现在9月中旬,为0.001 4 s/m,试验期均值为0.005 s/m。[结论]草地土壤细沟可蚀性的季节变化受根系密度和土壤黏结力的影响,随着根系密度与土壤黏结力增大,细沟可蚀性呈指数形式降低。试验区内草地土壤细沟可蚀性可用根系密度和土壤黏结力模拟(R2=0.604)。

The microstructure and formation of biological soil crusts in their early developmental stage

The biological soil crust serves as one of the biological factors contributing to the sand fixation in the Gurbantunggut Desert, the largest fixed and semi-fixed de- sert in China. This study was conducted to investigate the microstructure and formation of biological soil crusts which develop as a result of occurrence of cryptogams. One year after removal of biological soil crusts, the exposed surface could be fixed by bacteria, which make sand particles cohere by exopolysaccharides. The exopolysaccharides were mainly composed of glucose, mannitol, arabinose and galactose. The intension of pressure for this kind of crust is 13.42±1.38 Pa. After four-year recovery of the exposed sandy surface, the biological soil crust resulting from the colonization of soil surface by communities of filamentous cyanobacteria were mainly dominated by Microcoleus, which occurred as a clus- ter of filaments surrounded by a gelatinous sheath. At this developmental stage, the main contributors for sand fixation were changed from bacteria to filamentous cyanobacteria. Microscopic examination of this kind of crust revealed an intricate network of filamentous cyanobacteria and ex- tracellular polymer secretions, which binds and entraps mineral particles and finer particles on the filament surface. These effects enhance soil cohesion and resistance to erosion. The intension of pressure for this kind of crust is 32.53±3.08 Pa.