Molecular Soil Biology 2024, Vol.15, No.5, 227-235 http://bioscipublisher.com/index.php/msb 231 4 Discussion 4.1 Effect of water stress on growth This study reveals that onion plants exposed to water stress conditions had decreased growth and yield compared to wet conditions. There was a decrease in growth in terms of number of leaves and plant height under drought and waterlogging (Table 1). Khatiwada et al. (2020) reported that exposure of wheat to drought stress decreased root and shoot growth, and decline of biomass accumulation. It has been reported that drought stress caused reduced growth of seedlings, root and shoot dry weight reduction, undersized length of hypocotyl and poor vegetative growth in crops like Oryza sativa L., Pisum sativumL. and Medicago sativa L. (Okcu et al., 2005; Zeid and Shedeed, 2006). Drought caused Pisum sativum(pea) plants to grow slowly, have fewer leaves, and declined productivity (Fatima et al., 2024). Drought stress enforces modifications in fundamental morphology, physiology and biochemical aspects in plants. Cell division and differentiation, followed by cell enlargement, are the basic requirements of plant growth, but due to drought stress, cell elongation and mitosis are effected which results in reduced growth of plant (Farooq et al., 2009). Basu et al. (2016) described that cell growth is inhibited as turgor pressure is hindered due to drought stress. They further stated that water restraining conditions result in reduced cell elongation, primarily because of reduced water movement through xylem tissues and adjoining cells. Severity of drought lowers nutrient and water flow which brings about limited availability of nutrient for absorption by the root (Marschner, 2012). In an earlier report, Zea mays had a significant reduction in crop growth and development during waterlogged condition (Ren et al., 2014). Also, according to Xianquing Lin (2018), plant height, stem width, number of branches and floral bud of Brassica napus were significantly decreased by waterlogging. Liu et al. (2019) also revealed that there was decrease in plant height of Zeamays under waterlogged condition. The reduced number of leaves observed under waterlogged condition is similar to what was reported in Trifolium alexandrinum by Mensah et al. (2011). They stated that waterlogging affects the physiological and morphological functions of plants, thereby reducing the plant status such as the height, number of leaves, shoots and root growth. 4.2 Effect of water stress on biomass Drought condition led to a significant reduction in fresh and dry weight of shoot and root of onion, with the shoot more severely affected than the root (Table 1). In previous researches, frequent irrigation was observed to be necessary for good growth and yield performances of onion especially at bulbing stage (Bottcher et al., 1979; Choi et al., 1980). Gwandu and Idris (2016) reported that in 2012/2013 and 2013/2014 growing seasons, onions irrigated at 3 day interval had significantly the highest number of leaves, growth rate, bulb weight, bulb yield, cured bulb yield and bulb diameter compared to 5, 7 and 9 day intervals. They stated that 7 and 9 day irrigation intervals negatively affected growth and yield performances, and concluded that frequent application of water is required for good growth and yield performances of onions in Nigeria. Barley plants, when subjected to drought stress, showed decreased root and shoot length as well as their fresh and dry weights (Ahmed et al., 2013; 2015). It was also reported that fresh and dry weight of rice were repeatedly abridged due to limited water resource (Zhao et al., 2016). Drought was reported to have negative influence on photosynthetic apparatus of pea (Pisum sativum) which might be responsible for reduced biomass (Pandey et al., 2023). Shanxi (2012) reported that root dry weight of Hordeum vulgare L. were lower in waterlogged soil than those under proper watering. Armstrong et al. (2003) findings supported reduced fresh and dry weights of leaf and root parts of Marigold (Tagetes erecta L.) under waterlogged condition, highlighting the vulnerability of the leaf part to waterlogging stress. Waterlogging causes decrease in root biomass, hampering vegetative development and inducing plants organ senescence. This condition occurs whenever soil moisture levels go beyond the field capacity. In such cases, excess water saturates the soil pores in the presence of a very slim water layer on the soil surface. This stress usually have negative effect on the majority of terrestrial plants, limiting crop yield through changes in physical, chemical, biological and electrochemical properties of the soil (Ding et al., 2020).
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