Biological soil crusts: An eco-adaptive biological conservative mechanism and implications for ecological restoration

Biological soil crusts (BSCs) are highly complex associations of soil particles with mosses, cyanobacteria, lichens, bacteria, and fungi. BSCs affect many ecological processes, including infiltration and evaporation, soil erosion, vegetation succession, and nutrient cycling, and perform important ecological functions of ecosystems in arid areas. In the past 30 years, many studies on BSCs were conducted by researchers all over the world. This paper reviews the recent research progresses and frontier problems, and discusses the current controversial conclusions. The main ideas are as follows: (1) influenced by many macroclimate and micro-environment factors, BSCs are characterized by developmental complexity, composition diversity, and spatial heterogeneity. In any typical areas where exist all types of BSCs at different succession stages, it is of great significance to conduct comparable studies on BSCs and to explore if there exists a probable zonality for them. (2) BSCs not only exert positive impacts on soil fertility and soil erosion, but they also show controversial influences on the hydrological processes, especially on infiltration, evaporation, soil moisture, and vegetation succession such as survival, germination, emergence, and establishment. To understand the function-performing mechanisms of BSCs is helpful for the revealing of their action patterns and the comprehension of the implications of the patterns on ecological processes and restoration as well as clarification of existing controversial points. It will eventually contribute to the effective management and utilization of BSCs resources in a given region for large-scale ecological engineering.