**3.1 Effects of different treatments on soil physical indexes**

The soil bulk density after spraying algae culture solution in different proportions was shown in **Figure 2**. After spraying different proportions of algae culture solution, the bulk density of the 0–5 cm surface soil tended to decrease as a whole, among which, the soil bulk density of spraying mixed algae Microcolus vaginatus:

#### **Figure 2.**

*Effects of different treatments on soil physical indexes. CK T1: Microcolus vaginatus: Scytonema sinense: Phormidum lucidum 1:1:1; T2: Microcolus vaginatus: Scytonema sinense: Phormidum lucidum 3:2:1; T3: Microcolus vaginatus: Scytonema sinense 5:1; T4: Microcolus vaginatus; T5: Scytonema sinense; T6: Phormidum lucidum.*

Scytonema sinense: Phormidum lucidum 3:2:1 significantly decreased (P < 0.05). In conclusion, spraying different proportion of algal culture solution can reduce the soil bulk density, and the mixed algae with the ratio of Microcolus vaginatus: Scytonema sinense: Phormidum lucidum 3:2:1 has the best culture status. In the study of biological soil crusts in the Horqin Sandy Land of Inner Mongolia, algae crusts can significantly reduce the surface soil bulk density [21].
