Soil organic matter (SOM) decomposition is a key process that affects soil carbon storage and greenhouse gas emissions. Investigating the temperature sensitivity (Q₁₀) of SOM decomposition and its regulating mechanisms is important for improving predictions of SOM stability and carbon fluxes under future warming. Most studies on Q₁₀ are based on aerobic conditions, but little is known about how Q₁₀ varies in soils under oxygen limitation. This study compares Q₁₀ under oxic, suboxic, and anoxic conditions in three grassland soils and reveals the different roles of substrate carbon quality and nitrogen limitation in regulating Q₁₀. The findings were published in Soil Ecology Letters on January 18, 2024.

Xiaojuan Feng’s team at the Institute of Botany, Chinese Academy of Sciences, conducted soil microcosm incubation experiments to test how Q₁₀ varies in three grassland soils at different oxygen levels. They used three oxygen concentrations of 21%, 1% and 0% to simulate oxic, suboxic and anoxic conditions, respectively. They found that Q₁₀ did not show consistent patterns under different oxygen conditions, suggesting that other factors may override the effect of oxygen on Q₁₀. To delve deeper into these findings, they analyzed the soil properties by conducting a supplementary experiment and found that substrate carbon quality was a strong predictor of Q₁₀ in oxic soils, while nitrogen limitation was more important in suboxic and anoxic soils.

Professor Xiaojuan Feng, the corresponding author of the study, said, “We used incubated soils at varying temperatures to calculate Q₁₀. This method is increasingly popular in estimating Q₁₀, as it eliminates potential complications introduced by varying depletion rates of substrates at different, constant temperatures, which may affect soil C concentrations and microbial biomass in ‘equal-time’ incubations.”

“Our study shows that substrate carbon quality and nitrogen limitation may play roles of varying importance in determining Q₁₀ under various oxygen conditions. This implies that the response of SOM decomposition to warming may differ among soil types and moisture regimes due to differences in substrate availability and quality as well as nitrogen status.”

The study also highlights the importance of considering oxygen availability and its interactions with other factors when predicting soil carbon dynamics under climate change. Oxygen-deprived soils are widespread in wetlands and upland microsites, which contain a large proportion of global soil carbon stock. Understanding how Q₁₀ varies under different oxygen conditions will help improve the accuracy and reliability of soil carbon models and better inform management practices for soil carbon sequestration.

CAPTION

(A) Soil cumulative C-CO₂ emission and (B) Q₁₀ in Experiment 1 (mean and standard errors are shown; n = 3). Uppercase and lowercase letters indicate different levels among three temperature cycles and three O₂ levels, respectively (Tukey’s test, p < 0.05).

CAPTION

Relationship between (A) Q₁₀ and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄), and (B) Q₁₀ and L-leucine aminopeptidase (LAP) activity under three O₂ levels (n = 9). The SUVA₂₅₄ was positively related to Q₁₀ in oxic soils. The activity of LAP, an important N-targeting enzyme involved in releasing N from SOM, showed stonger correlated with Q₁₀ in suboxic and anoxic soils than in oxic soil based on a partial analysis. These results suggest that substrate quality had a strong influence on Q₁₀ in oxic soils, and N limitation likely influenced Q₁₀ variations in the suboxic and anoxic soils.