Flooding stress on plants: anatomical, morphological and physiological responses

STRIKER GG

In BOTANY (Editor: JK Mworia)

InTech - OpenAccess Publisher

Lugar: InTech Publisher, Rijeka-Croatia; Año: 2012; p. 3 - 28

Floods entail different stressful conditions for plants, which mainly depend on water depth and its duration. Adaptive traits of plants enabling survival under soil waterlogging and partial submergence, are those directed to oxygenation of submerged tissues (i.e. parts of shoots and entire root system), and the location of leaves above water to continue with carbon fixation. Aerenchyma formation and development of adventitious roots, with barriers to radial oxygen loss, appear as the most important features facilitating longitudinal oxygen transport to sustain root aeration, and thus continue with water absorption in anaerobic soils. Both the reorientation and lengthening of shoots towards a vertical position, determine a higher proportion of leaves surpassing the water level in order to capture oxygen and continue photosynthesizing. Maintenance of stomatal conductance on mild days guarantees the uptake of CO2 for carbon fixation, although on days of high atmospheric evaporative demand, the stomatal closure can be useful to regulate plant water homeostasis, which depends on the balance between water losses by transpiration and water uptake by roots. When water depth increases and plants are completely submerged, they can adopt two main strategies, namely LOES (low oxygen escape syndrome) and LOQS (low oxygen quiescence syndrome). The first involves the upward shoots elongation, which facilitates restoration of leaf contact with the atmosphere, and it is relevant for plants species (or ecotypes) selected in environments with shallow, prolonged floods. The second is a sit and wait strategy, where the plant remains quiescent during the submergence period by using its reserve carbohydrates conservatively for plant survival. When water subsides, plants showing LOQS resume their growth. The selection of this strategy is favoured in environments prone to deep, short floods. Future experiments assessing waterlogging and submergence responses of plants should include the combination of different flooding regimes. This would contribute to a better understanding of the costs and benefits related to particular combinations of traits conferring tolerance in variable flooding scenarios. Thus, a better comprehension of plant functioning under water excess, in a context that indicates a higher flooding occurrence during the years to come, would help to assist breeding programs as well as to define better management decisions for cultivation of crops and forage species in lands prone to flooding.