Soil Ecological Stoichiometry Characteristics of Picea crassifolia Forest at Different Altitudes in the Eastern Section of Qilian Mountains

Objective The article aimed to explore the response of soil nutrients and stoichiometry to altitude and soil layers in the P. crassifolia forest in the eastern section of the Qilian Mountains, and to reveal the limited factors for soil nutrients, in order to provide theoretical support for the ecosystem protection in the region.

Methods Four altitude gradients (2622 - 2664, 2741 - 2782, 2840 - 2872 and 2932 - 2950 m) were selected in the eastern section of the Qilian Mountains to analyze the differences of soil organic carbon (C), total nitrogen (N), total phosphorus (P), total potassium (K) contents and stoichiometric ratios in different soil layers (0 - 20, 20 - 40, 40 - 60, 60 - 80 and 80 - 100 cm) within different altitude ranges, as well as their relationships with environmental factors.

Results The average contents of soil organic C, total N, total P and total K in the P. crassifolia forest were 33.29, 3.96, 0.66, and 21.54 g kg⁻¹, respectively. The average values of C∶N, C∶P, N∶P, C∶K, N∶K, and P∶K were 8.74, 68.70, 5.72, 1.61, 0.19 and 0.03, respectively. As the altitude gradient increased, the soil organic C, total N, C∶N, C∶P, N∶P, C∶K and N∶K in each soil layer showed the increasing trend. The total P was relatively stable, while the total K and P∶K showed the fluctuating trend. As the depth of the soil layer increased, soil organic C, total N, C∶P and C∶K showed the decreasing trend at various altitude gradients, while total P, total K and C∶N remain relatively stable. N∶P, N∶K, and P∶K showed the fluctuating trend. Soil moisture content, altitude and pH were the dominant factors affecting the changes in soil organic C, total N, total P, total K contents and stoichiometry in Qinghai spruce forests, with explanatory rates of 65.80%, 25.10%, and 9.1%, respectively.

Conclusion The results indicated that soil organic C, total N, total P, total K contents and stoichiometric ratios of the P. crassifolia forest in the eastern section of the Qilian Mountains had undergone significant changes along the altitude gradient and soil depth. The P element was the limited factor for soil nutrients, and soil conservation work should be emphasized.