Three aerobic, asymbiotic, N₂-fixing bacterial strains, designated P205^T, P204 and P207, were isolated from a paddy soil in Yanting County, China. Based on 16S rRNA gene sequences, the three strains were closely related to Azotobacter chroococcum IAM 12666^T (=ATCC 9043^T) (99.00–99.79 % similarities). Strain P205^T formed an individual branch distinct from the other two newly isolated strains and other related type strains in phylogenetic analyses based on 16S rRNA gene and 92 core genes. The average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA–DNA hybridization (dDDH) values based on genome sequences of strain P205^T and A. chroococcum ATCC 9043^T, P204, P207 were near or slightly higher than the thresholds for species circumscription (95–96, 95–96 and 70 %, respectively), and the dDDH values were significantly lower than the threshold for delineating subspecies (79–80 %), which strongly supported that strain P205^T belonged to A. chroococcum but was a novel subspecies distinct from the type strain of A. chroococcum . This finding was further corroborated by distinct phenotypic characteristics such as growth in Luria–Bertani (LB) medium, carbon source utilization and chemical sensitivity to vancomycin. Therefore, strain P205^T represents a novel subspecies of Azotobacter chroococcum , for which the name Azotobacter chroococcum subsp. isscasi subsp. nov. is proposed with the type strain P205^T (=KCTC 72233^T=CGMCC 1.16846^T=CCTCC AB 2019080^T). The subspecies Azotobacter chroococcum subsp. chroococcum subsp. nov. is created automatically with the type strain ATCC 9043^T (=DSM 2286^T=JCM 20725^T=JCM 21503^T=LMG 8756^T=NBRC 102613^T=NCAIM B.01391^T=NRRL B-14346^T=VKM B-1616^T).

Nitrogen (N) is a key nutrient influencing wheat growth, grain yield, and quality. A long-term field experiment was conducted using cultivar Zhengmai 1860 to clarify the effects of N topdressing on grain protein composition, starch accumulation, and yield. Treatments included a basal N application of 150 kg ha⁻¹ (N1) combined with four topdressing rates at jointing: 37.5, 75, 112.5, and 150 kg ha⁻¹ (N1 + 37.5, N1 + 75, N1 + 112.5, N1 + 150). Nitrogen topdressing significantly affected the physiological and biochemical characteristics of grains at different spike positions. Amylopectin, globulin, soluble starch (SS), and soluble starch synthase (SSS) accumulated most under 75–112.5 kg ha⁻¹, with N1 + 75 showing the strongest response in basal and middle spike grains. Amylose and granule-bound starch synthase (GBSS) peaked at the middle spike under N1 + 112.5. Protein component (gliadin, glutelin, albumin), amino acids, glutamate synthase (GOGAT), and glutamine synthetase (GS) increased progressively with higher N rates, with maximum accumulation at N1 + 150. Nitrogen topdressing also enhanced spike number (5.05–37.13%), grains per spike (3.86–16.22%), and 1000-grain weight (2.72–5.79%), with the highest yield (9451.7 kg ha⁻¹) at N1 + 112.5. These results highlight the critical role of optimized N management in improving grain composition and yield in wheat.

Increasing species richness through rotation is considered a promising measure to enhance agroecosystem functions and services. However, the legacy effects of introducing legumes into a wheat–maize rotation in the North China Plain on soil microecology, especially the soil metabolome, in the succeeding wheat season have not been elucidated. This study established three cropping systems: (1) a continuous winter wheat–summer maize rotation (M), (2) a winter wheat–summer peanut (summer maize) rotation (PM), and (3) a winter wheat–summer soybean (summer maize) rotation (SM). The soil physicochemical properties, microbial communities, and metabolomes were analyzed at the stage of the succeeding wheat crop. Introducing peanuts or soybeans into a wheat–maize rotation significantly reduced the soil bacterial abundance and increased the soil fungal Shannon index. This rotation adjustment had a substantial impact on the structure and taxa composition of the soil microbial community. Crop diversification increased the number of total edges, the average degree, and the average number of neighbors in the soil microbial co-occurrence network. Different crop rotations significantly affected the soil metabolic profiles in the positive and negative ion modes. Crop diversification significantly reduced the abundance of coumarin and coumaric acid in the soils. In conclusion, introducing peanuts or soybeans into a wheat–maize rotation could increase the soil fungal community diversity, change the soil microbial community structure and taxa composition, increase the complexity of the soil microbial ecological network, and reduce the abundance of soil allelochemicals. Our study demonstrated the continuity of the impact of crop rotation on soil ecology, and revealed the ecological advantages of crop diversification from the perspective of soil microbiology and metabolomics.

Appropriate deep sowing holds significant potential in enhancing wheat production, particularly in dry and low-rainfall regions. Henan Province is a major winter wheat-producing area in China; evaluating the adaptability of wheat varieties to deep sowing through scientific methods is crucial to improve wheat production. This study investigates 26 wheat cultivars in Henan. By assessing key traits of seeds and seedlings at various sowing depths, we analyzed the effects of sowing depth on seed germination and seedlings. A comprehensive index for deep sowing tolerance was established using principal component analysis (PCA) and the membership function method, followed by the classification of the varieties according to their tolerance to deep sowing. The results indicated that, with increased sowing depth, seedling emergence time, coleoptile length, and coleoptile internode length increased, while seedling emergence rate, seedling height, leaf area, and shoot dry weight per unit area decreased. Based on PCA and membership function values, the 26 wheat varieties were classified into three categories: deep sowing tolerant, moderately tolerant, and intolerant, comprising 3, 19, and 4 varieties. This study provides valuable insights for optimizing wheat variety selection and improving sowing practices in Henan Province, offering both theoretical and practical contributions to local wheat production.