ABSTRACT
Waterlogging can occur in diverse environments and vary in intensity and duration from temporary to intermittent or continuous, and in timing during different periods of the plant growth cycle. It is not only a major constraint for crop productivity but strongly affects species distribution. Waterlogging is distinguished from flooding by the limitation of excess water to the root system. The adverse effects of waterlogging have been attributed principally to lowered oxygen supply, which is exacerbated by soil microorganisms that consume oxygen and may also diminish the supply of nitrate. Highly toxic microelements accumulate, as do CO
and ethylene. Tolerance to waterlogging can be defined either in physiological terms as maintenance of high biomass production or minimal growth reduction due to waterlogging, or in agronomic terms as achieving high grain yields or less reduction in yields under waterlogged conditions. Tolerance is thus a complex trait, undoubtedly involving numerous mechanisms at cellular and molecular levels. The initial step must be the capacity to perceive and transmit a signal to its point of action. Some progress has been made in understanding mechanisms of waterlogging stress sensing and regulation, although it is still unclear which of many possible signals and which sensing mechanisms are involved in eliciting an appropriate plant response. The subject of perception and signaling of soil water saturation (also see [1]) is discussed in the first part of this chapter. The mechanisms of anoxic tolerance have previously been extensively reviewed [2,3]. This chapter succinctly presents and updates our understanding of plant tolerance to waterlogging. It also reviews studies with an aim to improve waterlogging tolerance by genetic manipulation and finally, addresses how the level of plant tolerance to waterlogging can be evaluated. Varietal differences in tolerance at the germination stage often differ from tolerance at later stages of development, in support of the hypothesis that different mechanisms are involved. This chapter discusses mechanisms of waterlogging tolerance of plants with developed root systems at the vegetative stage of their development.
