Dynamics of crop residue mineralization and the priming effect in response to increasing temperature and initial soil carbon content

Crop residues are the main source of soil organic matter (SOM). However, their addition to the soil can induce the priming effect (PE), increasing the decomposition of native SOM. Predictions indicate that average global temperatures will increase between 1.4 and 4.4°C by the end of the century. This increase in global temperatures could result in changes in the dynamics of soil organic matter (SOM) decomposition, which could intensify the PE. In addition, the magnitude of PE may vary with the initial soil C content. The objective of this study was to assess the impact of temperature increase on the mineralization of crop residues and the occurrence of PE in soils with different initial C contents. The incubation experiment was conducted in a laboratory, in a completely randomized design, with four replicates. Residues of common vetch (Vicia sativa L.), labeled with ¹³C, were added to the surface (5 Mg ha^-1) in soils with a long history of cultivation under a no-till system. A Typic Paleudalf was utilized, collected from contrasting treatments in terms of initial C content (more - 2%; less - 1.3%), exhibiting minimal textural variation. The soils were incubated at10, 20, 30 and 40°C for 170 days. The apparent (AM) and real (RM) mineralization of residues were quantified continuously by determining the CO₂ and ¹³CO₂ released, respectively. The PE was calculated from the AM and RM data. The results obtained were subjected to analysis of variance and means were compared using the Tukey test (p < 0.05). Residue mineralization increased with temperature elevation in both soils. At 170 days, for temperatures between 10 and 30°C, the highest RM occurred in the less-C soil (41.4 to 45.3% of the added ¹³C) than in the more-C soil (38.3 to 44.0% of the added ¹³C). At 40°C, the highest RM was observed in the more-C soil (54.6% of the added ¹³C). However, the increase in temperature did not intensify the PE in both soils. The influence of residue addition on PE varied according to temperature and initial C content: in the less-C soil, the highest PE occurred at 40°C (274.6 mg C kg^-1), while in the more-C soil the highest PE was observed at 20°C (295.5 mg C kg^-1). These results indicate a variable effect of increasing temperature on the occurrence and intensity of PE in a soil with different initial C contents.