Abstract:

【Objective】This study was conducted to research the effect of rhizosphere oxygen environment on the root micromorphological structure of rice seedlings and its physiological mechanism, so as to lay a theoretical basis for the construction of ideal root type of rice.【Method】Two varieties, Chunyou 84 and Xiushui 09, were cultured in nutrient solution with different oxygen content (OC) levels (low oxygen, OC 0－1.0 mg/L; medium oxygen, OC 2.5－3.5 mg/L; high oxygen, OC >6.0 mg/L, continuous bubbling with atmospheric air, and normal conditions as CK, conventional hydroponics without oxygen regulation, the oxygen content in water approximately 0.3－2.5 mg/L) controlled by on-line dissolved oxygen meters. After different oxygen treatments, the biomass, root micromorphological structure, and some root physiological indexes (organic acid content, respiratory intensity, and so on) of rice seedlings were measured and analyzed.【Result】1) The proportions of fine roots (d₁, 0－0.50 mm; d₂, 0.51－1.00 mm; d₃, 1.01－1.50 mm) were more than 90%, which were particularly important for the construction of root morphology for rice seedlings. At medium oxygen level, the root length and root surface area of Chunyou 84 with diameter d₁ and d₂, and Xiushui 09 with diameter d₁ and d₃ were significantly higher than those of the control. 2) Low oxygen treatment reduced the biomass of shoot and root, inhibited the growth of fine roots (d₁), promoted the growth of coarse roots (d₅, 2.01－2.50 mm), reduced the root respiration rate and increased the secretion of organic acids. Medium and high oxygen treatments both increased the biomass of rice plants, but had different effects on root physiology. Medium oxygen treatment increased root respiration rate, while high oxygen treatment decreased. Different oxygen treatments reduced the content of root auxin (IAA). Especially, there was obvious difference between medium and high oxygen treatments with the control. The content of nitric oxide (NO) increased significantly under the high oxygen treatment, but there was no significant difference among other treatments. 3) The results of correlation analysis showed that the morphological indexes (root length, surface area, and volume) of the total and fine roots (d₂) of the two varieties were positively correlated with root organic acid secretion, respiratory intensity, and nitric oxide content, on the contrary, they were negatively correlated with auxin content.【Conclusion】Moderate increase of dissolved oxygen concentration (medium oxygen treatment) could improve the root respiration rate and organic acid secretion of rice seedlings, enhancing the root function and increasing the proportion of the length and absorption area of fine root (d₁－d₃), optimizing the root morphological structure. Therefore, appropriate cultivation measures could change the rhizosphere oxygen environment, regulate the micro morphological structure of rice roots at tillering stage and enhance the function of roots in field.

Key words: rice, rhizosphere oxygen environment, root physiology, root micro morphological structure

摘要：

【目的】研究根际氧环境对水稻幼苗根系微形态建成的影响及其生理机制，以期为水稻幼苗理想根型的构建提供理论依据。【方法】以春优84和秀水09为材料，用国际水稻所营养液配方进行水培试验。秧苗移栽一周后用在线溶氧仪(氮气、氧气调节)设定低氧(0~1.0 mg/L)、中氧(2.5~3.5 mg/L)和高氧(>6.0 mg/L，饱和溶解氧处理，在水稻生长过程中用充气泵连续向水体中充入空气)和常规水培(CK，不进行氧调节，水稻移栽一周后水中氧含量约为0.3~2.5 mg/L) 4个氧处理，研究水稻幼苗生物量、根系微形态结构、根系分泌有机酸、呼吸强度等指标。【结果】1）各处理水稻幼苗根系直径为d₁(0~0.50 mm)、d₂(0.51~1.00 mm)和d₃(1.01~1.50 mm)的细根占总根的比例均超过90%，对水稻苗期根系形态构建尤为重要。中氧处理后，春优84直径为d₁、d₂和秀水09直径为d₁、d₃的根的根长和根表面积均明显高于对照。2）低氧处理减少地上部和地下部生物量，抑制细根(d₁)生长，促进粗根(d₅, 2.01~2.50 mm)的生长，降低呼吸强度，增加有机酸分泌量。中氧和高氧处理后水稻植株的生物量均有增加，但生理反应不尽相同。中氧处理后水稻根系呼吸强度上升，而高氧处理后根系呼吸强度降低。各氧处理均减少水稻幼苗根系生长素(IAA)含量，中氧和高氧处理与对照间差异达显著水平。高氧处理显著增加根系一氧化氮(NO)含量，其他处理间差异不显著。3）相关分析结果表明，两供试品种总根和细根(d₂)的各形态指标(根长、表面积和体积)均与根系有机酸分泌量、呼吸强度、NO含量正相关，与生长素(IAA)含量负相关。【结论】适当增氧(中氧)处理增加水稻幼苗根系呼吸强度和有机酸分泌量，根系生理活性增强;增加细根(直径为0~1.50 mm)的根长、吸收面积的占比，优化其根系形态结构。因此，生产上可以通过栽培措施改变根际氧环境调控分蘖期水稻根系微形态结构，增强根系功能。

关键词: 水稻, 根际氧环境, 根系生理, 根系微形态结构