Regulatory Effects of Basic Seedling Density on Photosynthetic Characteristics, Root Morphology and Yield of Late-Sown Wheat Under Different Soil Types

Soil types vary considerably and sowing dates are generally delayed for wheat production in the Yangtze–Huaihe River Basin. To identify the differential yield responses to increased basic seedling density in late-sown wheat under different soil types, this study investigated the interactive effects of soil type (sandy loam vs. clay soil) and basic seedling density (2.8 × 106 and 4.5 × 106 grains hm−2) on yield formation, canopy photosynthesis, root morphology, and nitrogen utilization enzymes in late-sown wheat (cv. Yangmai 25). Increasing seedling density enhanced effective spike number, grain number per spike, tiller dynamics, leaf area index, aboveground dry matter accumulation, root activity, and grain yield; however, these increases were statistically significant only under sandy soil conditions. At the same density, sandy soil exhibited higher SPAD values, net photosynthetic rate, photosynthetic potential, and root morphological traits than clay soil. Although clay soil increased nitrogen utilization enzyme activities (NR, NiR, GS, and GOGAT) at heading and mid-filling stages, this advantage could not offset the yield disadvantages caused by restricted photosynthetic capacity and root development. Overall, soil type-dependent responses were detected for yield components, tiller traits, physiological characteristics and root morphological, indicating that soil conditions may influence the mechanisms through which density affects late-sown wheat.