Spatial variation in soil C/N/P stoichiometry and its ecological drivers along an east-west transect in the arid region of northwest China

Soil chemistry is often closely related with climates, its covering vegetation, and other local or regional soil traits. Based on samples from 146 arid sites, we explored how soil C/N/P content and their ratios varied along an east-west transect (75°E 106°E) in northwest China and their possible causes. The mean (±SE) contents of soil total C, N and P for overall sites were 11.4±0.7 mg g^-1, 0.40±0.02 mg g^-1 and 0.39±0.01 mg g^-1, respectively. The averaged soil C:N, C:P and N:P ratios were 28.4±1.3, 29.0±1.3 and 1.10±0.04, respectively. There were significant differences in soil C/N/P, and C:N, C:P among sandy, clayey, rocky, and solonchak deserts, while no significant differences in soil N:P among the four desert types. Soil total C/N/P were lowest in sandy deserts; while C:N and C:P were highest in solonchak deserts, which might be attributed to the high soil C in the latter deserts. Soil total C, C:N, and C:P decreased, but N:P increased with increasing longitude. Soil organic C, total N and P showed a curvilinear relationship with longitude, with their extreme values at 90 °E in Turpan Basin, an extremely arid region. Soil C, N, P, C:N, and C:P decreased, while N:P increased with mean annual precipitation (MAP). Soil C/N/P content, and C:N and C:P were negatively correlated with soil pH, while soil N:P was relatively stable with the change of pH. Climates (MAP and mean annual temperature, MAT), combined with soil data (desert types and soil pH) and fractional vegetation coverage (FVC), explained 31%, 21%, and 30% of the variation in soil C, N, and P contents, and 21%, 16%, and 4% of the variation in soil C:N, C:P, and N:P, respectively. MAT/MAP collectively explained less than 14% of the variations in soil C, N and P and their ratios. Desert type accounted for 2 23% of the changes in soil C/N/P and their ratios. Soil pH accounts for less than 16% of the variations in the stoichiometry of soil total C/N/P. However, a much smaller fraction of variation in soil C:N:P ratios was associated with FVC. The desert types explained more variation than other factors (MAP/MAT, pH and FVC) in soil C, N, P, C:N and C:P, while MAP explained more variation in N:P. In conclusion, this study shows a distinct longitudinal trend of soil total C/N/P stoichiometry in the arid area of China, which was assumed to be mainly shaped by the climatic and edaphic factors.