Elevation‐Driven Contrasting Mechanisms of Carbon‐Degrading Enzyme Activities Between Topsoil and Subsoil in Hengduan Mountain Forests

ABSTRACT The balance between oxidative and hydrolytic extracellular enzyme activities (Ox‐EEAs and Hy‐EEAs, respectively) serves as a key indicator of microbial substrate preferences, offering insights into the decomposition dynamics of diverse soil organic carbon (C) pools within forest ecosystems. Despite its significance, spatial patterns and environmental determinants of the ratio of Ox‐EEAs to Hy‐EEAs (Ox‐to‐Hy EEA ratio)—particularly across elevational gradients and soil horizons—remain poorly characterized in montane forests. In this study, we investigated the elevational variation (2100–3900 m a.s.l.) of Ox‐EEAs, Hy‐EEAs and the Ox‐to‐Hy EEA ratio in topsoil (0–10 cm) and subsoil (10–20 cm) across representative forest sites in the Hengduan Mountains. Both enzyme types exhibited an upward trend in activity with increasing elevation. Interestingly, the Ox‐to‐Hy EEA ratio followed a unimodal pattern in topsoil, whereas it declined monotonically with elevation in the subsoil, resulting in consistently lower values in the upper soil layer. Among all measured variables, soil total nitrogen (N) emerged as the primary driver influencing both enzyme categories across depths. In topsoil, however, soil physicochemical properties—especially ammonium N (NH 4 + ‐N)—exerted the strongest control over the Ox‐to‐Hy EEA ratio. In subsoil, the ratio was directly influenced by soil physicochemical properties (mainly soil pH) and soil stoichiometry (primarily soil organic C: total phosphorus ratio). Overall, our results reveal the depth‐dependent patterns and regulatory mechanisms of C‐degrading enzyme activities in dominant forest soils along an elevational gradient, thus providing insights into management practices of enhancing forest ecosystem services and functions in mountain forest ecosystems.