Biocrusts: Engineers and architects of surface soil properties, functions, and processes in dryland ecosystems

Biocrusts are photosynthetic biotic communities of cryptogams and microbes that aggregate minerals at the soil surface in many ecosystems. Due to their high tolerance to harsh environments, biocrusts are present in a wide range of habitats, but are especially representative ground covers in regions with restricted vegetation growth, such as drylands (hyperarid, arid, semiarid, and dry subhumid regions) where water is a limiting factor, or high latitude or altitude regions where cold is a limiting factor. Since biocrusts fulfill a large range of ecological roles particularly in modifying soil properties and regulating functions, their rehabilitation and management is believed to be a promising measure for combating land degradation. We organized this article collection to further highlight the importance of biocrusts and their fundamental roles in reshaping soil properties and multifunctionality in drylands and other ecosystems, and to elucidate the ways in which global change factors are influencing biocrust-soil systems. The special issue brings together 27 research articles pertinent to soil-biocrust interactions or biocrust response to global change and disturbance from 12 countries worldwide (10 papers from China, 6 papers from the USA, 2 papers from Spain, 2 papers from Australia, in addition to studies from Antarctica, Argentina, Brazil, Iceland, Iran, Mexico, Norway, South Africa, and Sweden). The discussed topics include biocrust roles in regulating soil hydrology (6 papers), reducing soil erosion (4 papers), affecting soil carbon fixation and respiration (2 papers), and influencing soil microbial biodiversity (5 papers). The responses of biocrusts themselves and their functions to trampling disturbance (2 papers), land use shifts (2 papers), and climate change (5 papers) are also emphasized. On the whole, we highlight the capability of biocrusts in reshaping most properties of surface soil, acting as engineers and architects of surface soil properties, functions, and processes in dryland or other harsh environments, and we recognize the necessity of their protection and consideration as valuable nature-based measures to combat soil and land degradation.