Water temperature instead of acclimation stage and oxygen concentration determines responses to winter foods

Field observations suggest that flooding events in the growing season are more detrimental than in winter. To clarify mechanisms producing these seasonal differences we analysed the role of plant acclimation, water temperature and oxygen concentration. We first tested the relative effects of seasonal acclimation and water temperature with three grassland species that differed in tolerance to summer floods (i.e. Rumex crispus, Rumex acetosa and Daucus carota). Our second experiment addressed the role of oxygen level relative to water temperature on biomass decay rate on a moderately intolerant species (i.e. R. acetosa). Irrespective of acclimation, biomass loss in warm water was considerably faster than in cold water. Given the concomitant decline in total non-structural carbohydrates, this was ascribed to the impact of water temperature on respiration rate. However, we only found a significant decline in carbohydrates for R. crispus and R. acetosa. D. carota seemed unable to access stored carbohydrates, which may explain its sensitivity for winter- and summer floods. Our second experiment provided no indication that the higher oxygen concentration may mitigate effects of flooding in cold water since a lower oxygen level of the water did not accelerate the rate of biomass loss. These findings indicate that temperature-driven respiration of carbohydrate reserves determines a species' response to winter flooding, whereas oxygen level or plant acclimation are unimportant. (c) 2005 Elsevier B.V All rights reserved.