Abstract:

Five typical vegetation types (i.e., coniferous forests, meadow grasslands, alpine shrubs, alpine meadows, and sparse vegetations of limestone flat) along a vertical belt of the Qilian Mountains were selected to explore the spatial elevational patterns of soil carbon, nitrogen, and phosphorus and their stoichiometric ratios. Results showed that: (1) The contents of total carbon (C), nitrogen (N), and phosphorus (P) at the 0-40 cm depth were 15.33-83.46, 1.63-7.76, and 0.41-0.66 mg·kg^-1, respectively. Soil C and N decreased gradually with increasing altitudes, following the order coniferous forests>meadow steppes>alpine shrubs>alpine meadows>sparse vegetations of limestone flat. Soil P in alpine scrubs was significantly higher than that in alpine meadows, but the other three vegetations showed no significant difference. (2) The contents of $\mathrm{NH}_{4}^{+}-\mathrm{N}$, $\mathrm{NO}_{3}^{-}-\mathrm{N}$ and available phosphorus at the 0-40 cm depth were 11.01-14.73, 2.78-12.46, and 4.35-13.57 mg·kg^-1, respectively. Ammonium was the main inorganic nitrogen form in all vegetation types. The nitrite content decreased gradually with increasing altitude. The content of soil available phosphorus was higher in sparse vegetations of limestone flats. (3) The ratios of soil C:N, C:P, and N:P at the 0-40 cm depth were 9.52-10.11, 29.89-320.24, and 3.18-29.63, respectively. Soil C:N decreased with elevation. Soil C:P and N:P were significantly lower in the soil of sparse vegetations of the limestone flat than in other vegetations, indicating that carbon and nitrogen were the limiting nutrients in the limestone flat. By contrast, the limestone flat was in a phosphorus-rich state. Elevational variations in soil C, N, and P contents and their stoichiometric ratios reflect the joint control of multiple environmental factors, thereby affecting the biochemical processes of soil C, N, and P.

Key words: vegetation type, elevations, soil physicochemical properties, eco-stoichiometry, Qilian Mountains