The effect of soil depth on stoichiometry was greater than that of elevation in Abies georgei var. Smithii forest in Southeastern Tibet, China

Abstract

High-frigid forest soil, as one of the most vulnerable terrestrial carbon reservoirs, exhibits a considerable sensitivity to climate change, potentially influencing soil carbon (C), nitrogen (N), and phosphorus (P) cycles significantly. However, the specific and quantitative impacts of elevation gradients on these soil stoichiometric parameters are yet to be fully elucidated and constitute the primary research objectives of this study. In this study, we investigated stoichiometric characteristics at soil depths of 0–10 cm, 10–20 cm, and 20–30 cm, and along gradients of elevation at 3500 m, 3900 m, and 4300 m a.s.l. In Abies georgei var. Smithii forest at the Sygera Mountains of southeastern Tibet. The results showed that: (1) Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) exhibited U-shaped changes with the increase in elevation, ranging from 53.14 to 70.73 g kg⁻¹, 2.78–3.32 g kg⁻¹, 0.41–0.62 g kg⁻¹, the content of nitrate nitrogen (NO₃⁻-N) in soil was not significantly different at different elevations; (2) The contents of ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), available phosphorus (AP) and available nitrogen (AN) in surface soil were the highest at different elevations; (3) Soil C:N showed a U-shaped change trend with the increase in elevation, while C:P and N:P decreased with the increase in elevation, and the ranges of C:N, C:P and N:P were 18.50–21.65, 116.69–156.38 and 5.47–7.70, respectively; (4) The soil depth had a more pronounced influence on C:N compared to elevation, whereas the elevation factor significantly impacted both C:P and N:P to a greater extent; (5) The soil of the Sygera Mountains is nitrogen-rich but phosphorus-restricted. These findings contribute to our understanding of the macroecological pattern of C:N:P in High-frigid forest ecosystems and provide valuable basic data support for forest management and conservation in this region in the future.