Seasonal differences in plant responses to flooding and anoxia

Strategies for surviving an environmental stress in winter can differ from those that provide protection from the same stress when it occurs in summer. During the growing season, escape mechanisms from stresses tend to prevail, as periods of adversity are generally brief. In winter, adverse environmental conditions have a high probability of persisting for lengthy periods and consequenctly, survival depends on tolerance. Spring is a period of uncertainty as to whether the risk of flooding has passed, and seeds differ markedly in their ability to resume germination if interrupted by re-imposition of winter conditions. When growing plants are flooded in summer, brief periods of accelerated anaerobic metabolism can alleviate energy shortages while improved aeration tissues develop, which then remove the dangers of prolonged anaerobiosis. By contrast, overwintering species, if they are highly tolerant of prolonged anoxia, may down-regulate metabolism when flooded and thus reduce the risk of exhausting carbohydrate supplies. Ventilation of underground organs in winter is still possible but is dependent on specialized mechanisms that can provide a through flow of air from emergent stems to buried or submerged organs. The tree form also presents metabolic and morphological problems for surviving wet conditions at critical seasons.