Biological soil crusts ( biocrusts) are ubiquitous living surface covers in arid and semi-arid regions． The
succession of biocrusts exerts significant influence on soil nutrient cycles owing to their functions of carbon and nitrogen
fixation． Therefore，soil ecological stoichiometry characteristics are likely to be affected by the succession of biocrusts． To
explore the effects of biocrusts on the contents of organic carbon (C)，total nitrogen (N)，total phosphorus (P)，and their
stoichiometric characteristics，biocrusts in six successional stages，totaling 59 sites，were chosen from the hilly Loess
Plateau region． Biocrusts and subsoils (0—2 cm，2—5 cm，and 5—10 cm) were sampled at each site． The contents of C，
N，and P were analyzed and their ratios were calculated． The results showed that biocrusts significantly affected the contents
of C，N，and P，and their ratios，which resulted in differences between biocrusts and the soils beneath them． Further，the
differences increased with the succession of the biocrusts． The contents of C，N，and P significantly increased in thebiocrust layers，which were significantly higher than that of the subsoils (0—10 cm)． The contents of C，N，and P in
biocrusts increased by 161%，127%，and 9%，respectively，in the later successional stage compared with that in the
earlier stage． The ratios of C/N，C/P，and N/P in biocrusts were all significantly higher than in the soils beneath them
(0—10 cm)． Variances of C/N were lower than that of C/P and N/P，with a range from 10．0 to 11．8． The C/P and N/P
ratios in the later successional stage of biocrusts were 2．4 and 2．1 times as high as that in the earlier successional stage，
respectively． The slope aspect was the major influencing factor for the ecological stoichiometry characteristics of biocrusts．
The ratios of C/N，C/P，and N/P were positively correlated with moss biomass and negatively correlated with soil bulk
density． The recovery of topsoil nutrients was improved owing to the succession of biocrusts and the improvement of recovery
appeared to be limited to a maximum depth of 2 cm under the biocrusts． Owing to the significant influences of biocrust
succession on soil nutrients and their stoichiometric characteristics，and the differences between biocrusts and their subsoil，
biocrusts play a crucial role for ecological restoration in arid and semi-arid regions． The results reveal the contribution of
biocrusts to nutrient cycles from the perspective of soil stoichiometric characteristics and the study provides scientific basis to
the ecological restoration and management in arid and semi-arid regions．
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