Biocrust wetting induced change in soil surface roughness as influenced by biocrust type, coverage and wetting patterns

Roughness significantly affects the hydrological and erosion processes in arid and semi-arid areas where biological soil crusts (biocrusts) are ubiquitous. Biocrusts influence roughness by the presence of the organisms and their swelling due to the wetting effect. However, the potential effects of biocrust coverage and wetting patterns on swelling induced roughness are elusive. This study aimed to determine the effects of biocrust type, coverage, and wetting patterns on wetting induced roughness (WIR) and to quantify the change process of WIR after wetting. Samples of cyanobacteria and moss with coverages categorized in five different classes were collected. High-resolution laser system samples were used to obtain measurements. The results showed that the mean swelling heights of cyanobacteria and moss were 0.068 mm and 0.415 mm, respectively, after 10 min of 2 mm water spraying. The swelling height of moss increased linearly (R-2 = 0.58, P < 0.001) with coverage. A mean negative WIR (-0.005 mm) was found for cyanobacteria, whereas it was 0.079 mm for moss. The WIR of moss was related to coverage (R-2 = 0.16, P = 0.003), and a critical coverage of moss existed between 20% and 40%, above which WIR increased sharply. The WIR of moss decreased as a power function of time after wetting (R-2 = 0.83). However, neither wetting-drying cycles nor drying durations influenced WIR for both cyanobacteria and moss crusts. The modifications of biocrust to soil surface are small. However, their potential influences on hydrology and erosion may help organisms in arid and semi-arid ecosystems make full use of the limited water, thus adapting to gradually changing environments.