Determination of optimal NH4+/K + concentration and corresponding ratio critical for growth of tobacco seedlings in a hydroponic system

Inherently, ammonium (NH4+) is critical for plant growth; however, its toxicity suppresses potassium (K+) uptake and vice-versa. Hence, attaining a nutritional balance between these two ions (NH4+ and K+) becomes imperative for the growth of tobacco seedlings. Therefore, we conducted a 15-day experimental study on tobacco seedlings exposed to different concentrations (47 treatments) of NH4+/K+ at different corresponding 12 ratios simultaneously in a hydroponic system. Our study aimed at establishing the optimal NH4+-K+ concentration and the corresponding ratio required for optimal growth of different tobacco plant organs during the seedling stage. The controls were the baseline for comparison in this study. Plants with low or excessive NH4+-K+ concentration had leaf chlorosis or dark greenish colouration, stunted whole plant part biomass, and thin roots. We found that adequate K+ supply is a pragmatic way to mitigate NH4+-induced toxicity in tobacco plants. The optimal growth for tobacco leaf and root was attained at NH4+-K+ concentrations 2-2 mM (ratio 1:1), whereas stem growth was optimal at NH4+-K+ 1-2 mM (1:2). The study provided an insight into the right combination of NH4+/K+ that could mitigate or prevent NH4+ or K+ stress in the tobacco seedlings

Differential Effects of Ammonium (NH₄⁺) and Potassium (K⁺) Nutrition on Photoassimilate Partitioning and Growth of Tobacco Seedlings

Plants utilize carbohydrates as the main energy source, but much focus has been on the impact of N and K on plant growth. Less is known about the combined impact of NH4+ and K+ nutrition on photoassimilate distribution among plant organs, and the resultant effect of such distribution on growth of tobacco seedlings, hence this study. Here, we investigated the synergetic effect of NH4+ and K+ nutrition on photoassimilate distribution, and their resultant effect on growth of tobacco seedlings. Soluble sugar and starch content peaks under moderate NH4+ and moderate K+ (2-2 mM), leading to improved plant growth, as evidenced by the increase in tobacco weight and root activity. Whereas, a drastic reduction in the above indicators was observed in plants under high NH4+ and low K+ (20-0.2 mM), due to low carbohydrate synthesis and poor photoassimilate distribution. A strong positive linear relationship also exists between carbohydrate (soluble sugar and starch) and the activities of these enzymes but not for invertase. Our findings demonstrated that NH4+ and K+-induced ion imbalance influences plant growth and is critical for photoassimilate distribution among organs of tobacco seedlings