The complex interactions between biocrust properties and rainfall characteristics give rise to partitioning of infiltration and runoff. In this review we examine primary mechanisms for runoff generation due to water repellency (WR), pore clogging (PC), soil texture and structural features including surface roughness. The primary hypothesis is that while WR plays an important role in runoff generation in humid regions, PC is a dominant process for runoff in arid and semiarid regions even under moderate rainfall intensities. Evidence suggests that the amount and properties of biocrust extracellular polymeric substances (EPS) dictate the rheological properties and swelling characteristics of the biocrust, which, in turn, govern the degree of pore clogging (due to surface swelling) and the resulting surface saturation. Changes in species composition of the main photoautotrophic component of the biocrust control the amount and properties of the embedded EPS. Disturbance or warmer climate may affect runoff generation via changes in biocrust species composition. These changes may not be necessarily long-lived when the disturbance is ceased or climate conditions revert to ‘original’ long term state.

生物结皮性质和降雨特征之间的复杂相互作用导致了入渗和径流的划分。在这篇综述中，我们研究了由于斥水性 (WR)、孔隙堵塞 (PC)、土壤质地和包括表面粗糙度在内的结构特征而产生径流的主要机制。主要假设是，虽然 WR 在潮湿地区的径流生成中起重要作用，但 PC 是干旱和半干旱地区径流的主要过程即使在中等降雨强度下。有证据表明，生物结皮细胞外聚合物 (EPS) 的数量和性质决定了生物结皮的流变性质和溶胀特性，进而决定了孔隙堵塞程度（由于表面溶胀）和由此产生的表面饱和度。生物结皮主要光合自养成分物种组成的变化控制着嵌入 EPS 的数量和性质。干扰或气候变暖可能会通过生物结皮物种组成的变化影响径流的产生。当干扰停止或气候条件恢复到“原始”长期状态时，这些变化可能不一定长期存在。