Previous studies have shown that zinc (Zn) accumulation in shoot and grain increased as applied nitrogen (N) rate increased only when Zn supply was not limiting, suggesting a synergistic effect of N on plant Zn accumulation. However, little information is available about the effects of different mineral N sources combined with the presence or absence of Zn on the growth of both shoot and root and nutrient uptake. Maize plants were grown under sand-cultured conditions at three N forms as follows: NO₃^– nutrition alone, mixture of NO₃^–/NH₄⁺ with molar ratio of 1:1 (recorded as mixed-N), and NH₄⁺ nutrition alone including zero N supply as the control. These treatments were applied together without or with Zn supply. Results showed that N forms, Zn supply, and their interactions exerted a significant effect on the growth of maize seedlings. Under Zn-sufficient conditions, the dry weight (DW) of shoot, root, and whole plant tended to increase in the order of NH₄⁺ < NO₃^– < mixed-N nutrition. Compared with NH₄⁺ nutrition alone, mixed-N supply resulted in a 27.4 and 28.1% increase in leaf photosynthetic rate and stomatal conductance, which further resulted in 35.7 and 33.5% of increase in shoot carbon (C) accumulation and shoot DW, respectively. Furthermore, mixed-N supply resulted in a 19.7% of higher shoot C/N ratio vs. NH₄⁺ nutrition alone, which means a higher shoot biomass accumulation, because of a significant positive correlation between shoot C/N ratio and shoot DW (R² = 0.682^***). Additionally, mixed-N supply promoted the greatest root DW, total root length, and total root surface area and synchronously improved the root absorption capacity of N, iron, copper, manganese, magnesium, and calcium. However, the above nutrient uptake and the growth of maize seedlings supplied with NH₄⁺ were superior to either NO₃^– or mixed-N nutrition under Zn-deficient conditions. These results suggested that combined applications of mixed-N nutrition and Zn fertilizer can maximize plant growth. This information may be useful for enabling integrated N management of Zn-deficient and Zn-sufficient soils and increasing plant and grain production in the future.

Splitting nitrogen (N) application is beneficial for achieving higher grain yields and N use efficiency (NUE), but the responses of N utilization efficiency of different maize cultivars to top-dressing N fertilizer rates are still unclear. This study investigated the effects of fertilization managements on N uptake and utilization derived from topdressing fertilizers of maize hybrids (Ludan981 and Denghai605) with contrasting NUEs. The N fate derived from topdressing fertilizer was determined using the ¹⁵N tracing method. Grain yields, dry matter and N accumulation of both maize hybrids were significantly increased under low N levels but decreased under high N levels. Under N-deficient and excess conditions, Denghai605 had higher NUE than Ludan981. The N rates of topdressing significantly affected N uptake and utilization, but no difference was detected between two maize hybrids, and excessive N use led to higher rates of N loss and residual in soil. The N metabolism enzyme activities did not differ between the two maize hybrids. Our findings suggest optimized N management strategies by adjusting topdressing N application rate and timing are necessary to increase NUE and to minimize environmental costs in maize cropping system.

Introduction: The selection and application of nitrogen-efficient maize hybrids have significantly bolstered contemporary food security. Nevertheless, the effects of heightened nitrogen fertilizer demand of these crops on the composition and assembly of soil microbial communities in agricultural production require further elucidation.Methods: In this study, the effects of four nitrogen fertilizer managements on rhizosphere bacterial and fungal community assembly, co-occurrence network and function of two maize hybrids (LD981 and DH605) were compared.Results and discussion: Findings revealed that the bacterial community was primarily shaped by deterministic processes, while stochastic processes played a pivotal role in fungal community assembly. N-efficient hybrid DH605 had a more stable microbial network than N-inefficient hybrid LD981. At N3 (130 g N/m²) rate, the bacterial and fungal community networks were the most complex but unstable, followed by N2 (87 g N/m²), N0 (0 g N/m²), and N1 (43 g N/m²) rates. Excessive nitrogen rate (N3) increased the relative abundance of denitrification genes nirK and norB by enriching nitrogen-related genus such as Nitrolancea and Nitrosospira. It led to an increase in the relative abundance of pathways such as cysteine and methionine metabolism and pyruvate metabolism. The effects of management practices (i.e. maize hybrids and N rates) on microbial communities were ultimately directly or indirectly reflected in microbial functions. Our findings illustrate the relationship between the appropriate selection of crop hybrids and management measures in optimizing rhizosphere microbial community assembly and promoting nitrogen use, which is necessary for sustainable food security.

Plant growth regulators (PGRs) enhance crop stress resistance but their roles in microbial-mediated phosphorus cycling within intercropping systems are unclear. Thus, We conducted a two-year field study using corn (Zea mays L. cv. Denghai 605) and soybean (Glycine max L. cv. Hedou 22) in fluvisols and luvisols soil according to World Reference Base for Soil Resources (WRB) standard. Under a 4-row corn and 6-row soybean strip intercropping system, three treatments were applied: a water control (CK), and two plant growth regulators—T1 (EC: ethephon [300 mg/L] + cycocel [2 g/L]) and T2 (ED: ethephon [300 mg/L] + 2-Diethyl aminoethyl hexanoate [10 mg/L]). Foliar applications were administered at the V7 stage (seventh leaf) of intercropped corn plants to assess how foliar-applied PGRs (T1/T2) modulated the soil phosphorus availability, microbial communities, and functional genes in maize intercropping systems. PGRs increased the soil organic phosphorus and available phosphorus contents, and alkaline phosphatase activity, but not total phosphorus. PGRs declined the α-diversity in fluvisols soil but increased the α-diversity in luvisols soil. The major taxa changed from Actinobacteria (CK) to Proteobacteria (T1) and Saccharibacteria (T2) in fluvisols soil, and from Actinobacteria/Gemmatimonadetes (CK) to Saccharibacteria (T1) and Acidobacteria (T2) in luvisols soil. Functional gene dynamics indicated soil-specific regulation, where fluvisols soil harbored more phoD (organic phosphorus mineralization) and relA (polyphosphate degradation) genes, whereas phnP gene dominated in luvisols soil. T1 stimulated organic phosphorus mineralization and inorganic phosphorus solubilization in fluvisols soil, upregulating regulation genes, and T2 enhanced polyphosphate synthesis and transport gene expression in luvisols soil. Proteobacteria, Nitrospirae, and Chloroflexi were positively correlated with organic phosphorus mineralization and polyphosphate cycling genes, whereas Bacteroidetes and Verrucomicrobia correlated with available potassium (AP), total phosphorus (TP), and alkaline phosphatase (ALP) activity. Thus, PGRs activated soil phosphorus by restructuring soil type-dependent microbial functional networks, connecting PGRs-induced shifts with microbial phosphorus cycling mechanisms. These findings facilitate the targeted use of PGRs to optimize microbial-driven phosphorus efficiency in strategies for sustainable phosphorus management in diverse agricultural soils.

The delay of leaf senescence, also known as the stay-green (SG) phenotype, is a trait closely associated with yield gain and resistance to many biotic/abiotic stresses. In order to increase the stress tolerance in maize, eight genetic background types were compared against the hallmarks of delayed senescence. The plant redox status and hormonal levels were tested among widespread SG and non-SG (NSG) maize lines in northern China. We found that SG maize lines showed greater activity of the reactive oxygen species (ROS) scavenging apparatus including leaf superoxide dismutases (SOD), peroxidases (POD), and catalases (CAT). Moreover, the concentration of malonaldehyde (MDA), a membrane lipid peroxidation marker, was significantly lower in SG than in NSG plants. For the hormone content, SG maize lines showed higher zeatin (ZR) and lower abscisic acid (ABA) after silking, resulting in a higher ZR/ABA ratio. Understanding the correlation between the stay-green trait and the corresponding hallmarks of delayed senescence is an important step in promoting SG to increase yield and stress tolerance. Our findings provide valuable insight into how to promote the SG trait in specific maize lines to increase yield and stress tolerance.