Oxygen Movement in Seagrasses

Abstract

Seagrasses are, like all vascular plants, obligate aerobes, which require a continuous supply of oxygen to sustain aerobic metabolism of both above- and below-ground tissues. Compared to their leaves, seagrass roots and rhizomes may experience oxygen deprivation for shorter periods, but these below-ground tissues exhibit physiological adaptations which allow them to rely temporarily on anaerobic fermentative metabolism (Pregnall et al., 1984; Smith et al., 1988). Aerobic respiration is energetically about 10 times more efficient than fermentative processes, which tend to accumulate ethanol, acetate, and other potentially toxic metabolites representing a threat to tissue survival (Smith et al., 1988; Crawford and Braendle, 1996). The meristematic tissues, located in the transition betweenwater column and sediment, are especially vulnerable to low oxygen supply and exposure to anaerobic metabolites due to their high metabolic activity and the continuous oxygen supply required for mitotic growth. In addition to the importance of oxygen inside seagrass tissues, maintenance of oxic conditions around roots may provide efficient protection against invasion of reduced toxic compounds and metal ions from the surrounding sediment (Armstrong et al., 1992; Crawford and Braendle, 1996; see also Marbá et al., Chapter 6). Accordingly, there are several benefits to plant performance in maintaining a rich oxygen supply to all tissues including roots and rhizomes.