Coupling of soil carbon and nitrogen dynamics in drylands under climate change

• Soil C and N stoichiometry increase with increasing altitude on the sunny slope. • Soil C and N stoichiometry are non-linear with altitude on the shady slope. • Altitudinal patterns of soil C and N dynamics vary across slope aspects. • Soil C significantly correlated with soil N on the sunny and shady slopes. • Soil C and N dynamics in drylands kept coupled under climate change. Climate change is predicted to be more dramatic in arid regions. Soil carbon (C) and nitrogen (N) dynamics maintain various functions in terrestrial ecosystems. It has been suggested that soil C and N dynamics are biologically coupled due to the strict proportions of C and N in organisms. However, whether dramatic climate change in drylands would break this coupling remained largely unknown. Given that climate change could occur over short distances in mountainous terrain, this study conducted a soil sampling across an altitude transect in Tianshan Mountains, China, which are the largest mountain system in drylands across the world. To avoid the disturbance of the influence of slope aspect, we therefore collected soil samples on the sunny and shady slopes of Tianshan Mountains. Our results showed that soil C and N concentrations and C:N ratio all increased with increasing altitude on the sunny slope and their changes were affected by temperature, soil sand content and precipitation. For the shady slope, soil C and N concentrations and C:N ratio all first increased then decreased along the altitude gradient. Soil pH, precipitation, temperature and soil sand content influenced soil C and N dynamics at altitude below 2650 m; soil pH and soil sand content affected soil C and N dynamics at altitude above 2650 m. These results indicated that soil C and N dynamics on the sunny and shady slopes both kept coupled under the condition of changing altitude. Furthermore, although the altitudinal patterns of soil C and N dynamics on the sunny and shady slopes were different, the correlations between soil C and N concentrations on these two slopes both were significant with a correlation coefficient of about 0.9. Hence, this study suggested that the coupling of soil C and N dynamics in drylands would still exist under climate change.