水氮耦合对春玉米苗期根系发育和吸收功能的影响及调控机制

The frequent drought stress during seedling stage has been a key environmental restricting factor for spring maize production in the northeast China. Water and nitrogen management shows significant individual and coupling effects on spring maize growth and grain yield under drought stress during the seedling stage, however, the regulation mechanisms on root development and absorption function are still unclear. In this project, field experiments and pot experiments will be conducted to create the natural and simulated drought stress conditions, and some advanced techniques including 3D-Monolith root sampling and observation in situ with minirhizotron will be used. Our objectives are to investigate the spring maize responses to different water and nitrogen management practices in terms of root spatial architecture, root morphological development, growth dynamic and physiological characteristics among the various root diameter classes, and the capacities to absorb soil water and nutrient, to evaluate the coupling effects of water and nitrogen on root development and absorption function of spring maize during the seedling stage. Furthermore, the relationships between root architecture, growth dynamic, physiological characteristics and its water and nutrient absorption capacities will be established to reveal the mechanisms of water and nitrogen coupling on absorption function of spring maize by regulating root development, and to determine the appropriate root regulating parameters and corresponding technical approaches. The results in this study would provide the supports of cultivation and fertilization techniques for spring maize in the northeast China to against drought stress, and also could enrich the theoretical understanding of coupling effect of water and nitrogen on crop root development.

苗期干旱胁迫频发是影响东北春玉米生产的重要生态限制因素。水分和氮素对苗期干旱胁迫下春玉米的生长及产量有显著效果并表现出耦合效应，但水氮耦合对根系发育和吸收功能的影响及调控机制还不清楚。本项目拟设置大田和盆栽试验利用苗期自然与模拟的干旱发生条件，采用3D-Monolith根系空间取样法和微根管原位监测系统等先进技术，研究不同水、氮组合条件下春玉米根系三维空间构型、形态发育特征、不同径级根系生长动态和生理特性、以及水分养分吸收能力等方面的变化，明确水分和氮素对春玉米苗期根系发育和吸收功能的影响及其耦合效应。另外，通过建立根系构型特点、发育特征、生理特性与水肥吸收能力之间的关系，阐明水氮耦合通过调控根系发育而影响其吸收功能的机制，明确合理的根系调控指标及途径。本研究结果可为东北春玉米抗旱减灾的栽培与施肥措施提供理论依据和技术支撑，还可丰富对作物水肥耦合根系调控机制的理论认识。

春旱频发是限制东北春玉米苗期生长的主要逆境，阐明水氮耦合对春玉米苗期物质分配与根系发育的调控机制，有助于优化水、氮管理以提高植株耐旱性、促进高产稳产。为此，本项目设置盆栽和田间试验，研究了水分、氮素对春玉米苗期生长、干物质累积、根系形态、空间分布及水肥吸收功能的影响，探讨并揭示了水氮耦合的根系调控途径。研究结果显示，水分和氮素对春玉米苗期植株干重、受旱反应、根系发育、根系形态及空间分布、水氮吸收及利用均具有显著交互作用。相比水分适宜条件，水分亏缺或过量均抑制了苗期植株生长、干物质累积、根系发育和氮素吸收。干旱胁迫促进根系下扎，增加下层土壤的根长分布，轻度和重度干旱条件下分别增加9.5%和6.9%，而水分过量条件下根系则主要集中于中上层土壤。增施氮肥促进了各水分条件下苗期植株生长，增加水分消耗和氮素吸收，但明显降低根冠比。施氮也显著影响了苗期根系生长和空间分布，减少苗期根系下扎而促进表层土壤的增殖，但不同水分条件下存在明显差异。干旱胁迫下施氮抑制了根系发育，显著降低根长和根表面积，减少水分获取而因此加重植株受旱表现。水分充足和过量条件下施氮促进根系发育但进一步增加了其在表层土壤的聚集。相比高氮处理，低氮处理的根长、根表面积及细根比例更高，中下层根系分布相对较多，因此水分和氮素利用效率均显著更高。所有水氮处理中，适度干旱与低氮处理的根系空间分布最为均衡，平均根长密度为0.30 cm/cm3，植株耐旱性较强，获得胁迫条件下最高的WUE（3.71 g/L）和NUE（12.7%）。相关分析发现，植株受旱反应、耗水量和NUE与根系形态均呈显著的相关关系，其中与根长的相关程度较高。综上所述，水分、氮素对春玉米苗期植株生长、物质分配及根系发育与水肥吸收功能具有显著影响及耦合效应。建议东北春玉米生产中减少氮肥基施用量并结合适度的自然或人工水分亏缺，以发挥水氮耦合效应，促进苗期根系下扎和细根增殖，优化根系空间分布，从而提高植株耐旱性和水氮利用效率。