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Broomcorn millet (BM), one of the earliest domesticated cereal crops originating in northern China, can tolerate extreme conditions, such as drought and high temperatures, which are prevalent in saline-alkali, arid, and barren landscapes. However, its adaptive mechanism to alkali stress is yet to be comprehensively understood. In this study, 80 and 40 mM standard alkali stress concentrations were used to, respectively, evaluate the alkali tolerance at the germination and seedling stages of 296 BM genotypes. Principal component analysis (PCA), Pearson's correlation analysis, and F-value comprehensive analysis were performed on the germination parameters (germination potential, germination index, germination rate, vigor index, root length/weight, sprout length/weight, and alkali damage rate). Based on their respective F-values, the BM genotypes were divided into five categories ranging from highly alkali resistant to alkali sensitive. To study the response of seedlings to alkaline stress, we investigated the phenotypic parameters (plant height, green leaf area, biomass, and root structure) of 111 genotypes from the above five categories. Combining the parameters of alkali tolerance at the germination and seedling stages, these 111 genotypes were further subdivided into three groups with different alkali tolerances. Variations in physiological responses of the different alkali-tolerant genotypes were further investigated for antioxidant enzyme activity, soluble substances, malondialdehyde (MDA) content, electrolyte leakage rate, and leaf structure. Compared with alkali-sensitive genotypes, alkali-tolerant genotypes had high antioxidant enzyme activity and soluble osmolyte content, low MDA content and electrolyte leakage rate, and a more complete stomata structure. Taken together, this study provides a comprehensive and reliable method for evaluating alkali tolerance and will contribute to the improvement and restoration of saline-alkaline soils by BM.

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Combined applications of plant residues and nitrogen (N) fertilizer in agroecosystems may increase N immobilization and reduce N loss through microbial propagation using fresh organic matter (FOM). However, the effects of different carbon (C) availabilities in FOM to microbes on the immobilization of two forms of fertilizer-N (NH 4 + -N and NO 3 − -N) are still not clear. In this study, starch (high availability) and cellulose (low availability) were used to represent different polysaccharides in crop residues, and their effects on the immobilization of two forms of fertilizer-N (NH 4 + -N and NO 3 − -N) were investigated. Following the additions of polysaccharides and 15 N (99.9 atom %) (2.1 g C kg −1 soil and 100 mg N kg −1 soil), we measured soil respiration and traced immobilized fertilizer-N over 48 days. The starch addition quickly depleted mineral N (on day 3) while cellulose caused a slow but continuous immobilization for 4 weeks. Despite the same amount of C and N input, the maximum fertilizer-N immobilization in the cellulose treatment was lower than in the starch treatment and accounted for 56% and 40% of added N for NH 4 + -N and NO 3 − -N forms, respectively. NH 4 + -N was preferentially immobilized over NO 3 − -N in the cellulose treatment during incubation, but it also occurred in the starch treatment when mineral N was sufficient. Our results suggest that it was not the abundance of C, but rather the availability of C to microbes, that strongly determined the rate and capacity of fertilizer-N immobilization. Further, the preferential immobilization of NH 4 + -N highlighted that the use of ammonium-based fertilizer can increase the level of fertilizer-N immobilization.