The influence of biological soil crusts on ¹⁵N translocation in soil and vascular plant in a temperate desert of northwestern China

Aims: Desert ecosystems are often characterized by patchy distribution of vascular plants, with biological soil crusts (BSC) covering interplant spaces. However, few studies have comprehensively examined the linkage between BSC and vascular plants through nitrogen (N) or element translocation. The objective of this study was to evaluate the ecological roles of BSC on N translocation from soil to the dominant herb Erodium oxyrrhynchum Bieb. (Geraniaceae) in a temperate desert in China. 

Methods: Isotopes (including ¹⁵N-Glu, ¹⁵N-NH₄Cl and ¹⁵N-NaNO₃) were used as a tracer to detect translocation of N in two types of desert soil (BSC covered; bare) to the dominant herb E. oxyrrhynchum. Three different forms of ¹⁵N-enriched N compounds were applied as a point source to small patches of BSC and to bare soil. And we measured isotopes (¹⁴N and ¹⁵N) and obtained the concentration of labeled-¹⁵N in both vascular plants and soils at different distances from substrate application 

Important Findings: Plants of E. oxyrrhynchum growing in BSC-covered plots accumulated more δ¹⁵N than those growing in the bare soil. Similarly, soil from BSC-covered plots showed a higher concentration of labeled-N irrespective of form of isotope, than did the bare soil. The concentration of dissolved organic N (¹⁵N-Glu) in E. oxyrrhynchum was higher than that of dissolved inorganic N (¹⁵N-NH₄Cl and ¹⁵N-NaNO₃). Soil covered by BSC also accumulated considerably more dissolved organic N than bare soil, whereas the dominant form of ¹⁵N concentrated in bare soil was dissolved inorganic N. Correlation analysis showed that the concentration of labeled-N in plants was positively related to the concentration of labeled-N in soils and the N% recorded in E. oxyrrhynchum. Our study supports the hypothesis that BSC facilitates ¹⁵N translocation in soils and vascular plants in a temperate desert of northwestern China.