Characteristics of spatial and temporal variability in the distribution of biological soil crusts on the Loess Plateau, China.

Biological soil crust (biocrust) is widely distributed on the Loess Plateau and plays multiple roles in regulating ecosystem stability and multifunctionality. Few reports are available on the distribution characteristics of biocrust in this region, which limits the assessment of its ecological functions. Based on 388 sampling points in different precipitation zones on the Loess Plateau from 2009 to 2020, we analyzed the coverage, composition, and influencing factors of biocrust across different durations since land abandonment, precipitation levels, topography (slope aspect and position), and utilization of abandoned slopelands (shrubland, forest, and grassland). On this base, with the assistance of machine learning and spatial modeling methods, we generated a distribution map of biocrust and its composition at a resolution of 250 m × 250 m, and analyzed the spatial distribution of biocrust on the Loess Plateau. The results showed that the average biocrust coverage in the woodlands and grasslands was 47.3%, of which cyanobacterial crust accounted for 25.5%, moss crust 19.7%, and lichen crust 2.1%. There were significant temporal and spatial variations. Temporally, the coverage of biocrust in specific regions fluctuated with the extension of the abandoned durations and coverage of cyanobacterial crust, while moss crust showed a reverse pattern. In addition, the coverage of biocrust in the wet season was slightly higher than that in the dry season within a year. Spatially, the coverage of biocrusts on the sandy lands area on the Loess Plateau was higher and dominated by cyanobacterial crusts, while the coverage was lower in the hilly and gully area. Precipitation and utilization of abandoned land were the major factors driving biocrust coverage and composition, while slope direction and position did not show obvious effect. In addition, soil organic carbon content, pH, and texture were related to the distribution of biocrust. This study uncovered the spatial and temporal variability of biocrust distribution, which might provide important data support for the research and management of biocrust in the Loess Plateau region.

Effects of temperature and initial pH on the growth of four dominant cyanobacteria species in biological soil crusts.

Biological soil crusts are of great significance for environment health and sustainable development in arid and semi-arid areas. Cyanobacteria, Microcoleus vaginatus, Scytonema sp., Nostoc sp., and Anabaena sp. are the dominant species in microbial community of biological soil crusts worldwide. Considering their broad application prospect, it is meaningful to cultivate them extensively. We examined the effects of temperature (10, 20, 25, 30, 35 ℃) and initial pH (4, 6, 8, 10, 12) on biomass and solution pH towards the four species of cyanobacteria with liquid culture in laboratory. The results showed that the biomass of the four cyanobacterial species grew slowly under 20 ℃, and that all species could grow in 25-35 ℃, with the highest growth rate at 25 and 30 ℃. The optimum culture temperature of different cyanobacterial species was slightly different. The optimum culture temperature was 25-30 ℃ for Scytonema sp. and Nostoc sp., and 30 ℃ for M. vaginatus and Anabaena sp. The four cyanobacterial species had a strong ability to adjust solution pH and proliferate in five different initial pH conditions. The highest maximum biomass and specific growth rate were recorded in the culture environment with initial pH of 4, while the lowest maximum biomass and specific growth rate were observed in initial pH of 12. Our results would provide scientific basis for the propagation of dominant cyanobacteria in biological soil crusts.