Spatial patterns in the C:N:P stoichiometry in Qinghai spruce and the soil across the Qilian Mountains, China

Knowledge of nutrient traits, especially carbon (C), nitrogen (N), and phosphorus (P), is essential for understanding the biogeochemical cycle and ecosystem functioning. However, spatial patterns in soil and plant tissues stoichiometry in the arid and semiarid forest ecosystem are not yet fully understood. Here, a regional-scale study was conducted on the Qilian Mountains to illustrate the macroecological patterns of soil C:N:P stoichiometry and the plant tissue N and P contents in Qinghai spruce (Picea crassifolia) forest and their driving forces. Soil C, N, and P contents and C:N:P ratios at all four soil depth layers (0-5, 5-10, 10-20, and 20-40 cm) showed depths, latitudinal, and longitudinal trends (p < 0.01), except for the soil P content and C:N ratios. The plant N and P contents and N:P ratios were found to be correlated with the latitude and longitude (p < 0.05). The N content and N:P ratios of plant tissue showed a negative correlation with the temperature (p < 0.05), which coincides with the temperature-plant physiological hypothesis. Additionally, the N and N:P of both the soil and plant tissue were positively correlated with precipitation (p < 0.05), which led to the plant tissue N and N:P and the soil TN and N:P being tightly related. Variation partitioning analysis revealed that the soil properties (39.31%) contributed more to the plant tissue N:P stoichiometry variations than climate (6.47%). The results demonstrated that the macroecological pattern of plant tissue N:P stoichiometry is mainly regulated by soil traits. These findings contribute to our understanding of the C:N:P macroecological pattern of forest ecosystems in arid regions, providing basic data for future forest cultivation and management in those areas.