Straw mineralization and carbon dioxide emissions in soils with different salinity levels

Straw application is widely used to reclaim saline soils. However, the characteristics of straw mineralization and its induced priming effects (PE) in saline soil are largely unknown. Thus, we conducted a 180-day saline soil incubation experiment to observe the characteristics of straw mineralization and CO₂ emissions. Four salinity levels, i.e., 3.0 g kg⁻¹ (BS), 5.0 g kg⁻¹ (LS), 10.0 g kg⁻¹ (MS), and 15.0 g kg⁻¹ (HS), were established, to which ¹³C-labeled maize straw was added at a rate of 5.0%. Results showed that the straw mineralization rate and the amount of potentially mineralized straw significantly decreased with increasing salinity (p < 0.05). Compared with BS, the cumulative CO₂ emissions, PE, and the amount of mineralized straw in LS, MS, and HS decreased by 3.6%–26.8%, 3.4%–26.5%, and 2.7%–15.6%, respectively. Simultaneously, increasing soil salinity prompted the earlier occurrence of the peak straw mineralization and PE. The contribution of straw mineralization to CO₂ emissions on the 1st day significantly decreased with rising salinity levels (p < 0.05), while the opposite change was observed from 5 days to 120 days. Although PE significantly decreased with increasing salinity, the duration of the effect of straw input on soil organic matter mineralization increased substantially in high-salinity soils. These findings reveal the influence of soil salinity levels on the straw mineralization process and CO₂ emission, which will help us assess and boost carbon sequestration in saline soils under straw input conditions.