Soil temperature dynamics and freezing processes for biocrustal soils in frozen soil regions on the Qinghai–Tibet Plateau

• Biocrusts exert important impacts on soil temperature in frozen soil regions. • The annual mean soil temperature of biocrustal soil decrease 0.6–1 °C within 100 cm. • Soil temperature reductions of biocrusts mainly occur in daytimes when thawing. • Biocrusts prolong the freezing duration by approximately 10–20 days within 100 cm. The relationship between soil temperature and its variations with different types of land cover are critical to understanding the effects of climate warming on ecohydrological processes in frozen soil regions such as the Qinghai–Tibet Plateau (QTP) of China. Biological soil crusts (biocrusts), which cover approximately 40% of the open soil surface in frozen soil regions, exert great impacts on soil temperatures. However, little attention has been given to the potential effects of biocrusts on the temperature characteristics, dynamics and freezing duration of soil in frozen soil regions. To provide more insight into this issue, an automatic system was used to monitor soil temperatures and dynamics at depths of 5, 30, 50 and 100 cm beneath bare soil and two types of biocrustal soils (soils covered with two types of biocrusts) on the QTP of China. The results showed that biocrusts play an important role in controlling the dynamics of soil temperatures. Biocrusts cause a 0.6–1 °C decrease in the mean annual temperature of soils down to a depth of 100 cm. The extent of the decrease in soil temperature was dependent on biocrust type, and dark biocrust showed a greater reduction in soil temperature than light biocrust. In addition, reductions in soil temperatures of biocrusts mainly occurred in daytimes of the thawing period, and this prolonged the freezing duration in the top 100 cm by approximately 10–20 days. The results of this study indicate that biocrusts maintain lower temperatures in the thawing period and slow the thawing of frozen soil in the spring, which helps to maintain the stability of the frozen soil. This information may aid understanding of the function of biocrusts in the frozen soil regions under global warming conditions.