Aerenchyma development and oxygen transport in the estuarine cordgrasses Spartina alterniflora and S. anglica

Abstract

Spartina alterniflora and Spartina anglica are intertidal cordgrasses that have the capacity to develop extensive aerenchyma systems. Aerenchyma may supply submerged portions of the plant with atmospheric oxygen as well as lower metabolic demands of the plant. These physiological benefits help to make Spartina grasses formidable invasive species in areas where they have been introduced. Aerenchyma development was investigated in S. alterniflora and S. anglica maintained in greenhouse experiments under flooded and drained soil conditions. Amounts of aerenchyma along the lengths of roots were calculated from digital images of serial root cross-sections using image analysis software. Maximal aerenchyma formation occurred in S. alterniflora following exposure to flooded conditions, while aerenchyma in S. anglica did not increase under the same conditions. Aerenchyma function was investigated by testing individual Spartina plants for their ability to transport oxygen from leaves to roots. Oxygen transport capacities provided information about the plants’ oxygen demands and the overall effectiveness of their aerenchyma systems. S. anglica plants were able to transport substantial oxygen to their roots, but no oxygen transport was detected in S. alterniflora plants under the same conditions. Increased aerenchyma formation in flooded S. alterniflora did not enhance oxygen transport and may function primarily in reducing metabolic oxygen demands.