Background/Objectives: Chinese cabbage (Brassica rapa ssp. Pekinensis, AA) growth and development is highly sensitive to cold temperatures. Prolonged low-temperature exposure during early growth stages can induce premature bolting, which reduces market quality and yield. Methods: Here, using comparative leaf RNA-seq transcriptome analysis of plants grown at 6, 9, 12, and 15 °C, we explored key genes and metabolic pathways regulating Chinese cabbage cold response. Results: RNA-seq transcriptome analysis identified a total of 1832 differentially expressed genes (DEGs) in the three comparison groups, with 5452, 1861, and 752 DEGs specifically expressed in the A6_vs_A15, A9_vs_A15, and A12_vs_A15 groups, respectively. KEGG enrichment analysis of DEGs showed that sulfur metabolism, secondary metabolites biosynthesis and photosynthesis pathways were mostly affected by cold stress. K-means clustering revealed distinct expression profiles among the DEGs enriched in cold stress response-associated clusters. Subsequently, DEGs were divided into 18 modules by WGCNA, whereupon co-expression genes that clustered into similar modules exhibited diverse expression and were annotated to various GO terms at different temperatures. Module-trait association analysis revealed M1, M2, M3, and M6 modules as key clusters potentially linked to vernalization-related processes. These modules harbored candidate hub genes encoding transcription factors (including MYB, bZIP, and WRKY), protein kinases, and cold-stress-responsive genes. Additionally, phenotypic analysis showed that 12 °C to 15 °C supported optimal growth, whereas <9 °C temperature inhibited growth. Physiological measurements showed increased antioxidant enzyme activity and proline accumulation at 6 °C. Conclusions: Overall, our study provides a set of candidate cold-stress-responsive genes and co-expression modules that may support cold stress tolerance breeding in Chinese cabbage.

Groundwater resources are scarce in the cold and arid regions of north China. Moreover, regional water resource replenishment without external sources remains difficult. This water deficit has become a major factor restricting the sustainable development of regional vegetable production. The effective utilization of rainwater harvesting for irrigated agricultural production is necessary to suppress droughts and floods in farming under the semi-arid climate of this area in order to both guarantee a stable supply of vegetables to the market in south and north China and promote the balanced development of regional agriculture–resource–environment integration. In this study, based on continuous simulation and Python modeling, we simulated and analyzed the water supply and production effects of irrigation with harvests and stored rainwater on tomatoes under different water supply scenarios from 1992 to 2023. We then designed and tested a water-saving and high-yield project for rainwater-irrigated greenhouses in 2024 and 2025 under natural rainfall conditions in northwestern Hebei Province based on the reference irrigation scheme. The water supply satisfaction rate, water demand satisfaction rate, and volume of water inventory of tomato fields under different water supply scenarios increased with the rainwater tank size, and the corresponding drought yield reduction rate of tomato decreased. Under the actual rainfall scenarios in 2024 and 2025, a 480 m² greenhouse with a 14.4 m³ rainwater tank for producing tomatoes irrigated with rainwater drip from the greenhouse film collected 127.7 and 120.5 m³ of rainwater, respectively. The volume of the rainwater tank was exceeded 8.3 and 8.0 times, and up to 93.8% and 95.0% of the irrigated groundwater was replaced; additionally, the average yield of the small-fruited tomato ‘Beisi’ was 50,076.6 kg·hm⁻² and 48,110.2 kg·hm⁻², reaching 96.1% and 92.3% of the expected yield. Conclusion: The irrigation strategy based on the innovative “greenhouse film–rainwater harvesting–groundwater replenishment” model developed in this study has successfully achieved a high substitution rate of groundwater for greenhouse tomato production in the cold and arid regions of north China while ensuring stable yields by mitigating drought and waterlogging risks. This model not only provides a replicable technical framework for sustainable agricultural water resource management in semi-arid areas but also offers critical theoretical and practical support for addressing water scarcity and ensuring food security under global climate change.

Groundwater overexploited areas of the North China Plain (NCP) have long faced the challenge of balancing agricultural water use and food security. Although seasonal fallowing can reduce water consumption, it also leads to underutilization of land and climatic resources, environmental risks such as wind erosion and dust dispersal, and losses in grain production. Integrating cover crops with multiple-cropping systems offers an important approach to improving soil ecological functioning and resource-use efficiency while ensuring food security. In this study, a field experiment was conducted with two one harvest per year systems, in which fallow (FM) or winter rapeseed (RM) was followed by spring maize, and two three harvests over two years systems, in which fallow (FMWM) or winter rapeseed (RMWM) was followed by spring maize and then by winter wheat and summer maize in the following year. We evaluated the effects of winter rapeseed cover and cropping-system adjustment on soil water dynamics, soil multifunctionality, grain yield, and crop water productivity. Winter rapeseed increased water consumption during the fallow period by 12.6–36.2 mm compared with the corresponding fallow treatments. However, abundant rainfall during the subsequent maize season compensated for the soil water deficit caused by winter rapeseed cover. On average, water consumption of spring maize was 86.6 mm higher than that of summer maize. Consequently, the higher water consumption of spring maize and the compensating effects of abundant rainfall offset the extra water use by winter rapeseed, resulting in no significant differences in two-year cumulative water consumption among treatments. Winter rapeseed increased soil available nutrient contents and enzyme activities. Soil alkali-hydrolyzable nitrogen, available potassium, and available phosphorus contents, as well as sucrase, urease, alkaline phosphatase, and catalase activities, were significantly higher under winter rapeseed cover than under the corresponding fallow treatments. Consequently, the soil multifunctionality index was also generally higher under winter rapeseed cover. In addition, RMWM achieved the highest grain yield, with two-year cumulative grain yield increasing by 56.1%, 47.6%, and 8.9% relative to FM, RM, and FMWM, respectively. Crop water productivity under RMWM reached 1.7 kg m⁻³, representing increases of 56.4%, 47.8%, and 9.4%, respectively. Overall, the system combining winter rapeseed cover with three harvests over two years improved soil functioning and increased grain yield and crop water productivity without significantly increasing two-year cumulative water consumption, providing a feasible cropping-system option for optimizing agricultural water use and safeguarding food security in groundwater-depleted regions of the North China Plain.