Acetylene reduction associated withZostera novazelandicaSetch. andSpartina alternifloraLoisel., in Whangateau Harbour, North Island, New Zealand

Abstract

Nitrogen fixation (acetylene reduction) was investigated in Zostera novazelandica Setch. and Spartina alterniflora Loisel., in the North Island of New Zealand. Moderate rates of acetylene reduction were found in sediments in which plants were growing (means ± 95% confidence limit: 15.2 ± 2.8 μmol C 2 H 4 m -2 h -1 for Zostera and 24.7 ± 4.6 |amol C 2 H 4 m -2 h -1 for Spartina). Activity was closely correlated with the dry weight of roots (r 2 = 0.65, N -15 for Zostera, and r 2 = 0.85, N = 10 for Spartina). Sediment close to the plant beds, but without plants, exhibited only low rates of acetylene reduction (2.9 ± 2.2 and 4.5 ± 1.0 pmolC 2 H 4 m 2 h -1 ,respectively). Sediments associated with Z. novazelandica and S. alterniflora in New Zealand exhibit moderate rates of nitrogenase activity compared to rates found in other countries. N fixation may contribute significantly to the nutrition of these plants in New Zealand estuaries.