Root morphology and partitioning of Fe accumulation in maize cultivars under low iron stress condition at seedling stage

Objectives The high pH and bicarbonate content in calcareous soil seriously affect the availability of Fe to crops, resulting in Fe deficiency, chlorosis, and reduction of yield. Fe-efficient maize cultivars are thus used as an effective way against Fe deficiency in calcareous soil. The root morphology of different Fe-efficient maize cultivars to adapt to low Fe stress were assessed in this study.

Methods A hydroponic experiment was carried out using four maize cultivars, two Fe-efficient cultivars (ZH2 and ZD619) and two Fe-inefficient cultivars (XY508 and CD418). Fe levels of very low (No Fe added, Fe0), low (Fe 10 μmol/L, Fe10, ) and normal (Fe 100 μmol/L, Fe100) were setup in nutrient solution. Root morphological characteristics, dry matter accumulation and Fe absorption and utilization by maize were measured at seedling stage.

Results Under low-Fe stress, the dry weight of root and plant, the Fe accumulation and relative absorption efficiency of maize seedlings were drastically reduced, while the root to shoot ratio and the Fe physiological efficiency increased significantly. The total root length, root surface area and root volume of Fe-inefficient cultivars were reduced whereas the root diameter was significantly increased under low Fe stress. Even though, the total root length and surface area of the Fe-efficient cultivars were comparable, the root volume increased significantly but the root diameter decreased significantly under the extremely low iron (Fe0) treatment as it was under the low (Fe10) treatment. The reduction in total root length, root surface area, root volume, root dry weight, dry matter per plant, iron accumulation, and Fe absorption efficiency of roots and the increase in root to shoot ratio of Fe-efficient cultivars were notably lower than those of Fe-inefficient cultivars. Correlation analysis results revealed that the Fe accumulation of maize seedlings was positively and significantly correlated with total root length, root surface area, root volume and root dry weight, but negatively correlated with root-shoot ratio. Among them, the correlation with total root length (R² = 0.8546) and root surface area (R² = 0.8983) was the strongest.

Conclusions Compared to the Fe-inefficient cultivars, Fe-efficient maize cultivars have larger total root length and root surface area at seedling stage, and higher root Fe absorption efficiency and physiological efficiency to adapt to low Fe stress, which could enhance absorption and utilization of Fe, thereby improve the adaptability to low-Fe environment.