Abstract:

Soil swelling affects soil system resistance and resilience by altering soil structure and hydrological processes. Biocrusts are important ecosystem engineers on the surface of arid sandy areas， which can accelerate soil formation and change soil physicochemical properties. But how the formation and development of biocrusts affect soil swelling is unclear. Our study use the method of spatial sampling instead of biocrusts' development time. Experiments were carried out on the biocrusts developed under the sand-fixing vegetation of different ages on the southern edge of the Tengger Desert. The sequence of the formation and succession of biocrusts was constructed （64， 39， 33 years and mobile sand dunes （0 years）， the method of simulating precipitation （0， 1， 3， 5， 10 mm） was used to measure the biocrusts （cyanobacteria， algal-lichen mixed crust， Bryum argenteum， Didymodon vinealis， and Syntrichia caninervis） Variation in swell height under different precipitation conditions. The sequence of biocrust formation and succession was constructed to elucidate the expansion changes of biocrusts in five succession stages at different developmental times under different precipitation conditions.The results showed that： （1） the formation of biocrusts increased the soil swelling height， and the average swelling height of the soil after crusting was 94 times that of quicksand， with an average of 0.939 mm. （2） the biocrusts and the succession stages of the biocrusts were both With the increase of its developmental age， the soil swelling height increased significantly （P<0.05）， which was mainly reflected in two aspects. Among them， D. vinealis are the most significant. The same crust is in different vegetation areas. With the increase of vegetation age， the effect of increasing the expansion of biocrusts after 39 years of development is the most significant， and the increase of algal-lichen mixed crusts is the most significant. （P<0.05）. （3） The increase of precipitation significantly increased the swelling height of soil under the cover of biocrusts （P<0.05）. The biocrusts （moss crusts） in the high succession stage were most sensitive to precipitation， especially within 3 mm. （4） Redundancy analysis showed that the biocrust succession stage was the most critical factor for soil swelling in arid sandy regions （RDA 1： 88.21%， RDA 2： 6.49%）. Our study revealed the changing trend of soil swelling under different successional stages of biological crusts and their developmental years， and explored the ways that biocrusts affect ecosystems by affecting soil swelling. It provides an important reference for a comprehensive understanding of the function of biocrusts to play an ecosystem.

Key words: soil swelling, biocrust, biocrust succession, Tengger Desert