Nitrogenase activities associated with macrophytes from a lacustrine and a freshwater estuarine habitat

The distribution and activities of diazotrophic epiphytes among and between species of freshwater emergent, submersed, and floating macrophytes were examined. We compared the aerobic and anaerobic macrophyte-associated nitrogenase activities from an urban lake, East Twin Lake, and an agriculturally-impacted freshwater estuary, Old Woman Creek Estuary, both in northern Ohio, USA. Epiphyte nitrogenase activity (NA) associated with macrophyte stems, petioles, or entire small plants was measured with the acetylene reduction technique. Aerobic epiphyte NA ranged from 5-760 times greater in the lake compared to the estuary. The differences between these activities probably reflect the higher combined inorganic nitrogen concentrations in the estuary. Anaerobic NA associated with the sediment portions of the macrophytes were virtually equal between the two systems but not between macrophyte species. Nuphar advena supported more near/in-sediment anaerobic NA than did either Nymphaea odorata or Nelumbo lutea. All macrophyte species tested positive for aerobic epiphyte NA. This activity was documented for two species not previously reported: the American lotus, N. lutea, and the floating liverwort, Ricciocarpus natans. (C) 1997 Elsevier Science B.V.