The soil carbon pool in saline–alkali land is a research hotspot in the field of agricultural environmental science. However, there are no systematic conclusions regarding the paddy soil carbon pool in the Yellow River Delta in China. Therefore, this study focused on the paddy soil in the Yellow River Delta; using statistical analysis methods and establishing relevant models, we explored the dynamic changes in organic carbon and its active components and their influencing factors in saline paddy fields under two planting patterns. The results showed that there was no significant difference in the dissolved organic carbon (DOC) content between the two planting patterns. However, the rice–wheat rotation pattern was more conducive to the accumulation of microbial biomass carbon (MBC). The soil organic carbon (SOC) and readily oxidizable organic carbon (ROC) contents increased under the two patterns and different salinization treatments. The results of the redundancy analysis and the random forest model indicated that SSA was the key environmental parameter affecting SOC and its active components under the single-season rice pattern. Under the rice–wheat rotation pattern, soil sucrase activity (SSA) was also a key environmental factor for predicting the SOC content, while electrical conductivity (EC) contributed the most to the active components of SOC. The PLS-PM model showed that the soil carbon sequestration capacity could be improved by enhancing soil enzyme activity under the rice–wheat rotation pattern, while the influence of the soil environment on SOC and its active components was not obvious under the single-season rice pattern. In general, the rice–wheat rotation pattern has agricultural advantages in terms of maintaining ecological balance and can be widely promoted in this region. The results of this study have important practical significance for promoting the green and low-carbon development of agriculture in the Yellow River Delta region and also lay a foundation for subsequent long-term positioning observations and studies on multi-factor interactions.

Soil salinization is one of the most important factors limiting the sustainable development of global agriculture. As the core driving force of the soil carbon cycle, soil-carbon-metabolism-related enzyme activity is very important for soil ecological balance and fertility enhancement. To explore the spatial and temporal variation characteristics and coupling mechanisms of soil water, salt, nutrients and enzyme activities in different salinized wheat fields in the Yellow River Delta, field experiments were conducted in Dongying City, Shandong Province. The results showed that the soil moisture content of the low-salt wheat field was higher and that the salt content of three wheat fields was concentrated in the 0–20 cm and 80–100 cm soil layers. Here, soil nutrients and enzyme activities are concentrated in the 0–20 cm topsoil, with significant differences in different degrees among salinized wheat fields at the different growth stages of wheat. Overall, invertase activity (S-SC) and amylase activity (S-AL) presented a trend of low salt > high salt > medium salt, while cellulase activity (S-CL) presented a trend of medium salt > low salt > high salt. Redundancy analysis showed that available potassium (AK) (67.6%) and electric conductivity (EC) (21.2%) in the low-salinity wheat field, total nitrogen (TN) (48.6%) and AK (28.8%) in the medium-salinity wheat field, and EC (67%) and soil organic matter (SOM) (19%) in the high-salinity wheat field contributed the most to soil enzyme activity. This study provides a theoretical basis for the management and sustainable development of different salinized wheat fields in the Yellow River Delta.