Slope position affects nonstructural carbohydrate allocation strategies in different types of biological soil crusts in the Gurbantunggut Desert

Background and aims Biological soil crusts (biocrusts) play a vital role in desert ecosystems. The sand-dune slope position crucially affects biocrust growth and development. This paper investigates the effect of slope position on nonstructural carbohydrates (NSCs) in biocrusts in the Gurbantunggut Desert. Methods Samples were collected from the eastern and western slopes and the bottom of the slope. Biocrust coverage, soil physicochemical properties, and NSCs were assessed. Results The NSCs were more affected by the slope position in the lichen crusts than the algae crusts. The contents of NSCs and their components in the lichen crust were the highest at the bottom of the slope, while those of the algae crust were the highest at the eastern slope. In the algae crusts, soluble sugar, starch, and NSCs were positively correlated with the electrical conductivity, soil organic carbon, and ammonium nitrogen. In the lichen crusts, they were significantly positively correlated with the soil water content, electrical conductivity, total nitrogen, total phosphorus, and ammonium nitrogen. The structural equation model revealed that the most important factors affecting the NSCs were the changes in the soil nutrients caused for the algae crusts and the soil moisture and temperature for the lichen crusts. Conclusions The slope position indirectly influenced the NSC variations in the biocrusts through the soil physicochemical properties, but the key factors affecting the NSC in the different types of biocrusts were different. In conclusion, biocrusts adapt to environmental discrepancies arising from slope position by modulating the NSC content and distribution pattern.