Molecular Soil Biology 2025, Vol.16, No.6, 297-305 http://bioscipublisher.com/index.php/msb 301 5 Case Studies on Root Architecture Modifications in Maize 5.1 Research study: impact of root architecture on nitrogen uptake After three consecutive years of field trials, the root growth condition of the large root system test cross combination T-213 was significantly better. During the tasseling stage, the root length density, root surface area and root dry weight of T-213 were all higher than those of the small root system control T-Wu312, with an increase of approximately 9.6%~19.5%. Although the distribution position of the root system in the soil did not change significantly, after silk production, the plant's absorption of nitrogen increased significantly, and the grain yield also rose by 17.3%. The content of nitrate nitrogen in the soil layer below 30 cm decreased significantly (Mu et al., 2015). Under high-nitrogen and low-nitrogen conditions, a comparison was made between 7 inbred lines and 12 hybrids, and it was found that the overall root system performance of the hybrids was stronger. Nitrogen absorption efficiency (NUpE) is significantly positively correlated with multiple root system indicators, including root length (RL, r = 0.73***), root surface area (RSA, r = 0.67***), root volume (RV, r = 0.66***), root density (RD, r = 0.52***), and root dry weight (RDW). r = 0.92***, and the correlation coefficients were all relatively high (r = 0.80***). Nitrogen use efficiency (NutE) is mainly affected by aboveground traits, such as the activities of nitrate reductase and glutamine synthase, as well as photosynthetic indicators such as leaf area index (LAI) (Jan et al., 2025). Combinations such as Zheng58×PH4CV, 444×PH4CV, 444×MO17 and B73×MO17 exhibit larger root systems and higher NUpE in the early nutritional stage. Under the conditions of 0 N and 150 kg N ha-1, the pillar root Angle and crown root Angle of the newly bred hybrid increased by 7.9%~19.3% respectively compared with the old variety, the number of crown roots increased by 21.4%~30.5%, and the 95% root weight depth D95 increased by 8.5%~10.5%. This type of RSA hybrid vigor enhances N absorption before silk casting and N internal efficiency (NIE) during grain filling (Li et al., 2024b). At 40 μmol/L NO3 -, the abovground and underground biomass of the N - high-efficiency genotype was almost unaffected, while the abovground and underground dry matter of the N - low-efficiency genotype decreased by approximately 58% and 64% respectively. The former is manifested as the lateral root strategy of "few branches + long elongation". The total lateral root length contributes the most to improving NUE, followed by the axial root length. The N efficiency is significantly positively correlated with the lateral root and axial root elongations at different depths (Wang et al., 2022). F44 has longer crown roots, larger root surface area and volume, as well as higher number and density of lateral roots. It has a strong ability to transport and assimilate nitrate nitrogen, and the activities of NR and asparagine synthase in its roots are significantly higher than those in B73. B73 prefers ammonium N, and in the B73×F44 hybrid, the preference for root form and N form of B73 is completely dominant (Dechorgnat et al., 2018). 478 has a greater total root length, higher root dry weight and higher root-crown ratio both at high and low N in the field. Especially at low N, more and longer axial roots make its N accumulation and yield higher than those of W312. However, the ¹³NO3 - flux per unit root length and the N absorption rate were actually lower than those of W312 (Liu et al., 2009). 5.2 Case study: root traits and phosphorus efficiency in maize Under low P conditions in the field, the correlation coefficient between PupE and PUE was 0.48~0.54, while under hydroponic conditions, the correlation coefficient between root morphology indicators and PupE was 0.25~0.30, but had no relation to PutE. Two QTL clusters (Cl-BIN3.04 a/b) were located in the bin3.04 segment of chromosome 3, carrying both PUE, PupE and root trait QTLS. The favorable alleles all originated from the "large root + high PupE" parent. Using these two clusters for label-assisted backcrossing selection and breeding, advanced backcrossing lines with a single cluster were obtained, and their PUE in low-P fields was on average 22%~26% higher than that of the receptor parents. The L224 series that simultaneously integrated Cl - bin 3.04A and Cl - bin 3.04B exhibited higher PupE both in hydroponics and in the field. High and low P treatment experiments were carried out in large columnar POTS in greenhouses and fields using RIL carrying "many short (MS)" or "few long (FL)" lateral root types. Under low P conditions, the P absorption of the MS type system in the greenhouse is 89% higher than that of the FL type system, and the aboveground biomass is 48% higher. Under low P in the field, the 95% root weight depth (D95) of the MS system is 16% shallower than that of FL, the root
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