Waterlogging and Plants

Growth and development of plants are severely influenced by the stagnant waterlogged condition. Plants grown on arable farmland or watery environment show differential responsiveness to the stress. The level of variation in response to waterlogging is a critical issue regulating abundance and distribution of plants [1]. Rice (Oryza sativa L.) is particularly tolerant to submergence, whereas tomato (Solanum lycopersicon L.) is highly intolerant [2]. Within species, Mentha arvensis is more tolerant than Mentha piperita [3]. Whether genus or species approximately 16% of the fertile areas of the world are affected by soil waterlogging [2] and average yield loss due to waterlogging is estimated to be 20–25% and can exceed 50% depending on the stage of plant development [4].

The ability of excess water to damage plants may seem counter-intuitive since water is chemically benign. However, certain physical properties of water, most notably its ability to interfere with the free gas exchange, can injure and kill plants when they are totally submerged or even when only the soil is waterlogged [5]. Under normal conditions, water dissolves about 230 mmol•m–3 oxygen, and hypoxia occurs when the oxygen (O2) level falls below 50 mmol•m–3 [6]. Within 1 hour of flooding, the O2 partial pressure declines from 20.8 to 7.9 kPa, and further decreases to 1 kPa after 1 day of flooding [6]. If waterlogging persists for a prolonged period it confers enhanced anoxic stress and is thought to impose a variety of adverse effects on plants, which can upset plant physiology and normal metabolism. Along with O2, CO2 and ethylene also diffuse slowly in water [7]. Soil chemistry also alters due to reduced gas movement and because of growth of microorganisms which ...

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...l features like increased height, aerenchyma and adventitious root formation. These traits are controlled by ethylene, auxin, ABA and GA. Carbohydrate consumption and mobilization is a major factor affecting shoot elongation under waterlogging. But these characters differ when we analyze a genus, rather a species within that genus which ultimately distinguishes tolerant from susceptible varieties. The root cause is identified as the variation in genetic structure which determines transcriptional regulation.

Upstream and downstream signal transduction components operating in tolerant varieties need to be characterized further. Molecular approaches should be combined with breeding programs for generating stable tolerant varieties. Knowledge about genetic variation in flooding tolerance should be of utmost importance keeping in mind the global climate change scenarios.