Agronomy

Increasing plant density raises maize yield potential but intensifies within-canopy shading and accelerates lower-leaf senescence. The role of nitrogen (N) allocation among C4 photosynthetic components in this process remains poorly quantified. We hypothesized that optimizing N partitioning toward the C4 carboxylating and decarboxylating enzymes sustains photosynthetic function under dense planting. A two-year field experiment (2024–2025) tested two hybrids (planophile JK857 and compact, density-tolerant ZD958), three plant densities (60,000, 75,000 and 90,000 plants ha⁻¹) and three N rates (0, 150 and 300 kg N ha⁻¹). Leaves were sampled at 10, 25, 40 and 55 days after silking (DAS) from the upper, middle and lower canopy layers and analyzed for photosynthesis, senescence physiology, and the allocation of leaf N to Rubisco, phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK). Grain yield responded strongly to N rate (F = 2415.6, p < 0.001) and density (F = 70.2, p < 0.001); the compact ZD958 out-yielded the planophile JK857 by 10.1% at 90,000 plants ha⁻¹, and raising the density from 75,000 to 90,000 plants ha⁻¹ reduced yield by 10.0% in JK857 but only 5.3% in ZD958. The steep vertical gradient of intercepted PAR within the canopy, rather than N supply, dominated inter-layer differences in light availability: at 55 DAS, the upper, middle and lower layers intercepted 59.5%, 42.7% and 26.2% of the PAR incident at their own tops, equivalent to 59.5%, 16.9% and 5.8% of above-canopy PAR. The proportion of leaf N allocated to C4 enzymes increased with the N rate (38.3% to 48.2% in the middle layer, p < 0.001) and decreased with density (44.8% to 42.1%, p < 0.001), and remained nearly conservative across layers despite a 2.2-fold gradient in total leaf N. Structural equation modeling indicated that high density was associated with lower net photosynthesis mainly through reduced specific leaf N and C4-enzyme N proportion, whereas the N rate was associated with higher photosynthesis and yield mainly through improved N partitioning rather than through canopy light interception. Optimizing within-leaf N partitioning toward the C4 apparatus thus helps sustain post-silking photosynthetic function and stabilize yield in dense-planted maize, although the timing of senescence itself was developmentally regulated.

Cadmium (Cd) accumulation in food crops poses a major threat to safe agricultural production, whereas selenium (Se) biofortification demands precise regulation of Se concentrations in edible tissues. Biochar–Se co-application can reconcile these dual objectives, yet stable performance across cropping systems remains challenging. This review evaluates biochar–Se combined strategies. We discuss how soil chemical and rhizosphere processes control Cd immobilization and Se bioavailability, linking them to plant metal transport, Se assimilation, antioxidant defense, cellular Cd sequestration and photosynthetic responses. Existing studies demonstrate that these combined treatments can simultaneously lower Cd concentrations and elevate Se levels in edible crop tissues. Nevertheless, treatment outcomes depend on biochar properties, Se species and dosage, application practices, soil characteristics, and crop genotype. Reduced Cd uptake does not always coincide with desirable Se biofortification, yield or quality gains; individual treatment efficacy cannot guarantee synergism. Risks including excess Se accumulation, potential Cd remobilization and economic costs restrict field adoption. Multi-site, multi-season replicated field trials are urgently required to optimize treatment regimes and validate the long-term efficacy of this remediation and biofortification approach.

There are significant differences in yield potential between northern and southern Xinjiang. This experiment explored the differences in high-yield performance and the main limiting factors of Gossypium hirsutum L. and Gossypium barbadense L. Field experiments were conducted jointly in the early–medium-maturing cotton subregion (Alar) and the early-maturing cotton subregion (Shihezi) in Xinjiang. Canopy structure, dry matter accumulation and partitioning, and yield formation were evaluated. The results showed that high yield of G. hirsutum was mainly attributed to a 19.30–24.42% increase in boll number per plant in Shihezi, despite a 15.43% decrease in harvested plant density. During the critical yield formation period, the peak leaf area index (LAI) reached 6.10–6.49. Total biomass and stem dry matter allocation increased by 47.70% and 19.66%, respectively, resulting in a 14.98% increase in seed cotton yield. For G. barbadense, yield increase depended on increases in harvest plant density and boll number per plant, leading to a 39.01–76.04% increase in total boll number. However, the maximum reproductive dry matter accumulation rate was reduced by 19.34–20.08% in Alar compared with Shihezi, resulting in a 14.63% reduction in boll weight. The maximum LAI ranged from 4.67 to 5.97 and occurred 13 days earlier in Alar. The stem allocation decreased by 29.27%, whereas reproductive allocation increased by 27.15%. Therefore, increasing boll number per plant essential for improving G. hirsutum yield, maintaining a higher LAI, enhancing total biomass accumulation, and increasing dry matter allocation to stems may have the potential to further increase yield, whereas the potential benefits of optimizing planting density require further experimental validation. For G. barbadense, high yield is achieved by synergistically increasing total boll number increasing by 39.01–76.04%, whereas increasing boll weight is essential for overcoming yield limitations. Maintaining an appropriate LAI and improving dry matter partitioning may further enhance yield. These findings provide insights into the yield formation characteristics of the tested G. hirsutum and G. barbadense cultivars under the experimental conditions at Alar and Shihezi during 2024–2025.