Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, Arak University, Arak, Iran.
BMC Plant Biol. 2024 Apr 13;24(1):281. doi: 10.1186/s12870-024-04943-7.
The presence of oxygen in the growth medium is absolutely essential for root development and the overall metabolic processes of plants. When plants do not have an adequate oxygen supply for respiration, they can experience a condition known as hypoxia. In order to investigate the impact of different nitrogen forms and varying oxygen levels in nutrient solutions on the growth, photosynthesis, and chlorophyll fluorescence parameters of bell pepper plants, a comprehensive study was conducted. The experiment was designed as a factorial experiment, considering two main factors: nitrogen forms (calcium nitrate and ammonium sulfate) with a fixed nitrogen concentration of 5 mM, and the oxygen levels of the nutrient solutions (ranging from 1.8 ± 0.2 to 5.3 ± 0.2 mg. L).
The study examined the effects of nitrogen (NH and NO) application on various parameters of vegetative growth. The results demonstrated that the use of ammonium (NH) led to a reduction in the most measured parameters, including the fresh and dry mass of both the root and shoot, at low O concentrations of 1.8 ± 0.2; 2.6 ± 0.2 and 3.8 ± 0.2 mg. L. However, an interesting observation was made regarding the impact of oxygen levels on root growth in plants grown with nitrate (NO). Specifically, the highest levels of oxygen significantly increased root growth in NO-fed plants. Additionally, the application of NH resulted in an increase in chlorophyll concentration in the leaves, particularly when combined with high oxygen levels in the nutrient solution. On the other hand, leaves of plants fed with NO exhibited higher photosynthetic rate (A), intrinsic water use efficiency (iWUE), and instantaneous carboxylation efficiency (A/C) compared to those fed with NH. Furthermore, it was found that NO-fed plants displayed the highest instantaneous carboxylation efficiency at oxygen levels of 3.8 and 5.3 mg. L, while the lowest efficiency was observed at oxygen levels of 1.8 and 2.6 mg. L. In contrast, NH-grown plants exhibited a higher maximal quantum yield of PSII photochemistry (F/F), as well as increased variable fluorescence (F) and maximum fluorescence (F), compared to NO-grown plants. Interestingly, the NO-fed plants showed an increase in F/F, F, and F with the elevation of oxygen concentration in the nutrient solution up to 5.3 mg. L.
This study showed that, the growth and photosynthesis parameters in bell pepper plants are sensitive to oxygen stress in floating hydroponic culture. Therefore, the oxygen level in the nutrient solution must not be lower than 3.8 and 5.3 mg. L in NH and NO -supplied culture media or nutrient solutions, respectively.
氧气在生长介质中的存在对植物的根发育和整体代谢过程是绝对必要的。当植物没有足够的氧气进行呼吸时，它们会经历一种称为缺氧的情况。为了研究不同氮形式和营养液中不同氧水平对甜椒植株生长、光合作用和叶绿素荧光参数的影响，进行了一项全面的研究。该实验设计为析因实验，考虑了两个主要因素：氮形式（硝酸钙和硫酸铵），固定氮浓度为 5 mM，以及营养液的氧水平（范围为 1.8±0.2 至 5.3±0.2 mg.L）。
该研究检查了氮（NH 和 NO）应用对各种营养生长参数的影响。结果表明，在低氧浓度 1.8±0.2、2.6±0.2 和 3.8±0.2 mg.L 时，使用铵（NH）会降低大多数测量参数，包括根和茎的鲜重和干重。然而，有趣的是，在硝酸盐（NO）培养的植物中，氧水平对根生长的影响。具体来说，最高水平的氧气显著增加了 NO 喂养植物的根生长。此外，在营养液中高氧水平下，NH 的应用增加了叶片中的叶绿素浓度。另一方面，与 NH 喂养的植物相比，NO 喂养的植物表现出更高的光合作用速率（A）、内在水分利用效率（iWUE）和瞬时羧化效率（A/C）。此外，发现 NO 喂养的植物在氧水平为 3.8 和 5.3 mg.L 时表现出最高的瞬时羧化效率，而在氧水平为 1.8 和 2.6 mg.L 时则观察到最低效率。相比之下，与 NO 培养的植物相比，NH 培养的植物表现出更高的 PSII 光化学最大量子产量（F/F）以及可变荧光（F）和最大荧光（F）的增加。有趣的是，随着营养液中氧浓度升高至 5.3 mg.L，NO 喂养的植物的 F/F、F 和 F 增加。
这项研究表明，甜椒植株的生长和光合作用参数对浮式水培培养中的氧气胁迫敏感。因此，在 NH 和 NO 供应的培养基或营养液中，营养液中的氧水平不得低于 3.8 和 5.3 mg.L。
