Relationship Between Anatomical and Metabolic Responses to Soil Waterlogging in the Coastal GrassSpartina patens

Abstract

Flooding responses in Spartina patens propagated from plants collected in dune, swale, and marsh habitats were examined in a 63 d time-course experiment. Leaf growth rates and anatomical and metabolic responses did not depend upon plant population, suggesting that there were no physiologically significant differences in soil waterlogging responses among source populations. Flooding resulted in significant declines in soil redox potential and root specific gravity (indicating increased root aeration). Root alcohol dehydrogenase activity (ADH, a measure of the capacity to ferment ethanol) increased within 3 d of flooding, then exhibited a significant decline as root aeration increased (i.e. as root specific gravity decreased). However, maximal aerenchyma development (50% of the root volume after 29 d) reduced but did not eliminate hypoxic stress in the roots. When plants that were flooded for 63 d were drained, ADH activity fell to levels equivalent to drained controls. These results support the following inferences: (1) Soil waterlogging dramatically increases root ADH activity. (2) Impact of soil waterlogging on root metabolism diminishes once internal root aeration increases. (3) Under severe chemically-reducing soil conditions, root aerenchyma formation, which adjusts to the prevalent degree of soil waterlogging, cannot provide roots with sufficient oxygen to support aerobic respiration completely.