玉米早期根系构型及其生理特性对土壤水分的响应

为了探明玉米早期根系结构及其对土壤水分的生理响应,揭示玉米幼苗的抗旱机理,以蠡玉18为材料,采用盆栽试验,设置轻度胁迫(LS)、中度胁迫(MS)、重度胁迫(SS)和正常供水(CK)4个水分处理,系统研究从播种开始持续水分处理对夏玉米苗期根系形态结构及活力、保护酶系统及生理调节物质的影响。结果表明:随着水分胁迫程度的加剧,玉米根长、根表面积、根体积和根干重等各形态指标较CK下降幅度逐渐增大,不同水分胁迫使夏玉米苗期根系结构存在差异。轻度和中度胁迫显著增加了细根(0.05—0.25 mm)根长和根表面积比例,重度水分胁迫显著降低粗根(0.50 mm)根长与根表面积比例。玉米苗期根冠比、根系活力和丙二醛(MDA)含量随水分胁迫程度的增强而上升,随着胁迫时间的延长,根冠比逐渐降低。根系可溶性蛋白含量随土壤水分含量的下降而下降,MS、SS处理较CK显著降低(P0.05)。夏玉米根系中SOD对水分胁迫较CAT、POD更敏感,轻度水分胁迫下主要依赖CAT、中度水分胁迫下主要依赖POD、重度水分胁迫下主要依赖SOD来降低氧化伤害;且重度胁迫下,随着胁迫时间的延长保护酶活性下降。苗期玉米通过增加根冠比、增强根系活力和不同保护酶活性及降低可溶性蛋白等渗透调节物质来协同减少水分胁迫的危害。

Effects of water stress on the root structure and physiological characteristics of early-stage maize

As the third major grain crops behind the wheat and rice, maize (Zea mays L.) plays an important role in the source of food and industrial raw materials. In arid and semi-arid regions of northwest China, the abundant solar energy provide a tremendous potential of maize yields, but it is out of harmony with rainfall resource insufficient, especially in the early-stage (sprout and seedling stages) of summer maize. As a plant organ in absorbing soil water and minerals, crop roots could change the distribution, structure, and protective enzyme contents to responding the drought stress. However, little is known about how these indexes affect the plant ability comprehensively. To study the effects of sustained water stress on maize root structure and physiological characteristics, and reveal the drought resistance mechanism for early-stage (sprout and seedling stages) of summer maize. a maize (Liyu 18) pot experiment contains four water treatments was conducted: (i) mild water stress (LS, 70% of the field moisture capacity); (ii) moderate water stress (MS, 50% the of field moisture capacity); (iii) severe water stress (SS, 30% of the field moisture capacity); (iv) and normal water supply (CK, 85% of the field moisture capacity) as the control. The results showed that the biomasses of aboveground part and root were both significantly (P < 0.05) decreased under water stress treatments in seedling stage of summer maize, and root structure also significantly (P < 0.05) difference. And the length, surface area, volume, and dry weight of maize root were all decreased with the increase of water stress. Compared with CK, fine root length (diameter, 0.05-0.25 mm) and root surface area ratio significantly (P < 0.05) increased in LS and MS, and thick root length (diameter > 0.50 mm) and root surface area ratio decreased in SS. Root-shoot ratio, root activity, and malondialdehyde content increased with the increase of water stress, which could improve the drought resistance of crops. The crop allocated more photosynthetic product to the roots to relieve the long time water stress, so the root-shoot ratio decreased with the extending of stress time. Compared with CK, the soluble protein content of maize root under MS and SS treatments was significantly (P < 0.05) decreased with a reduction of soil moisture in seedling stage, which may be attributed to the protein synthesis was limited by the water stress. The results also showed that the protective enzyme activity of maize root increased by the soil water stress to reduced the damage of the active oxygen accumulation. The superoxide dismutase (SOD) of summer maize root was more sensitive to soil water stress than catalase (CAT) and peroxidase (POD), and the root reduced the oxidative damage mainly depend on CAT under LS, POD under MS, and SOD under SS. Under the SS, the enzyme activity of maize root decreased with the extending of stress time. In general, for early-stage (sprout and seedling stages) of summer maize, the adverse effects of water stress can be reduced comprehensively by the increased of root-shoot ratio, improved of root and protective enzyme activity, and decreased the amount of osmotic regulation substances (i.e. soluble protein).