Effects of elevated O3 and CO2 on the relative contribution of carbohydrates to soil organic matter in an agricultural soil

• Elevated O3 alone and combined with elevated CO2 decreased the total soil neutral sugars.
• Elevated O3 promoted the relative contribution of microbe-derived carbohydrates to SOM.
• N application determined the plant-microbial relationship on carbohydrate dynamics.

As labile fraction of soil organic matter, soil carbohydrates are sensitive to environmental changes due to their high turnover rates. The effects of elevated O3 and CO2 on the concentration and composition of soil carbohydrates in agroecosystems have been rarely studied. The present experiment was conducted to investigate the dynamics of the concentration and composition of neutral sugars in soil under the influence of elevated O3 and CO2 with different N application rates (150 kg N ha−1 and 225 kg N ha−1). Our results showed that elevated O3 decreased soil carbohydrate accumulation, with the effect being more pronounced with high than with low N application rate. Elevated O3 significantly increased the ratio of (mannose + galactose)/(arabinose + xylose), indicating that elevated O3 promoted the relative contribution of microbe-derived carbohydrates to soil organic matter (SOM). The high N application rate further increased the contribution of microbe-derived carbohydrates to SOM under elevated O3 conditions. However, elevated CO2 had no effect on soil carbohydrate accumulation and little effects on carbohydrate composition in the study soil, regardless of N application rates. The elevated O3-induced effects were not altered by elevated CO2 at the low N application rate, and the change in composition mediated by elevated CO2 was observed only at the high N application rate. Our results suggest that elevated O3 affected soil carbohydrate accumulation and their composition and that the effects on composition were mediated by elevated CO2 and N application rates.