Unexpected responses of SOC decomposition and its temperature sensitivity to plant invasion across soil layers: Implications for plantation understory management

Abstract

Soil organic carbon (SOC) decomposition is a key process in regulating carbon (C) sequestration in plantation ecosystems, and its sensitivity of temperature (Q₁₀) is essential for predicting C-climate feedback. However, plantations exhibit heightened vulnerability to plant invasion due to resource fluctuations and frequent disturbances, which may significantly affect SOC decomposition. The mechanisms by which plant invasion influences SOC decomposition rate and its Q₁₀ in plantations remain poorly understood, particularly in subsoil layers. To fill the knowledge gap, we sampled topsoil and subsoil in poplar plantations, both with and without Solidago canadensis invasion, and conducted a 28-day incubation experiment. The results indicated that S. canadensis invasion increased SOC decomposition rate and its Q₁₀ in both soil layers. Notably, the primary drivers of SOC decomposition rate and its Q₁₀ vary with soil depth. In the topsoil, increased enzyme activities were the dominant factors driving SOC decomposition rate and Q₁₀. In contrast, in the subsoil, increased substrate availability played a more significant role. These findings challenge the assumption that plant effects are limited to surface soils and demonstrate that SOC dynamics in subsoil are as sensitive to plant invasion as those in topsoil, due to increased substrate availability. This emphasizes the importance of considering subsoil processes when evaluating the impacts of plant invasions. Additionally, the results suggest that we should pay attention to plantation understory vegetation management to prevent the harmful effects of plant invasions on SOC dynamics under future climate warming scenarios, effects that enhance carbon dioxide (CO₂) emissions and exacerbate regional C-climate feedbacks.