The mineralization of soil organic carbon (SOC) plays a vital role in regulating atmospheric CO₂ concentrations, and its sensitivity to temperature increase (Q₁₀) determines the direction and magnitude of climate-carbon cycle feedback. However, Q₁₀ values exhibit large variability. Moreover, in riparian zones, where soil oxygen levels are highly dynamic owing to frequent flooding, the spatial pattern of Q₁₀ and its mechanisms are still obscure. These uncertainties and knowledge gaps hindered us from accurately predicting soil carbon loss and its response to global warming.

Researchers from Wuhan Botanical Garden investigated the latitudinal and vertical variations in Q₁₀ for aerobic and anaerobic mineralization and determined the dominant influencing factors. Topsoil (0~20 cm) and subsoil (40~60 cm) samples from 30 typical riparian zones along a 3500 km latitudinal transect across eastern China were collected.

The results showed that anaerobic carbon mineralization showed a higher temperature sensitivity than aerobic mineralization, and Q₁₀ varied with climate and soil depth. Q₁₀ increased with latitude for aerobic metabolism but decreased for anaerobic metabolism, and Q₁₀ for aerobic metabolism decreased with soil depth. Overall, the anaerobic SOC mineralization in subsoils from warmer areas exhibited the highest Q₁₀. These findings suggested that permanently or seasonally flooded areas or deep soil layers in southern China may experience severe carbon losses as warming continues, and the use of Q₁₀ from the topsoil alone to represent the entire soil profile would overestimate or underestimate carbon release.

The abundance of genes responsible for the degradation of both the most resistant C (lignin) and the most labile C (carbohydrate esters and starch) increased with latitude, especially in topsoil. In contrast to oxic conditions, the genes responsible for anaerobic C (acetate) degradation were less abundant in the temperate zone, regardless of soil depth.

The Q₁₀ value under oxic conditions was positively correlated with soil electrical conductivity, pH, and sand proportion but negatively correlated with soil density and soil water content. Whereas, under anoxic conditions, the Q₁₀ value was positively controlled by the abundance of the acetate degradation genes, mean annual precipitation and mean annual temperature, and the proportion of sand.

Overall, this study highlights that the discrepancies in aerobic and anaerobic SOC metabolism and the carbon cycling process at different soil depths might play a non-negligible role in affecting the assessment of global carbon emissions under climate change.

This study has been published in Soil Biology and Biochemistry entitled “Temperature sensitivity of aerobic and anaerobic organic carbon mineralization varies with climate and soil depth in riparian zones”. Dr. LU Mingzhu is the first author, Prof. LIU Wenzhi and Associate Prof. MA Lin are the corresponding authors.This research was funded by the National Natural Science Foundation of China and the China Postdoctoral Science Foundation.

 The latitudinal and vertical patterns of aerobic and anaerobic Q₁₀ and the driving factors (Image by WBG)