In situ acetylene reduction assays of nitrogenase activity associated with the emergent halophyte Spartina alterniflora Loisel.: Methodological problems

Abstract

An in situ technique for assaying nitrogenase activity (acetylene reduction) in plant—soil systems was tested in a salt marsh. While it was possible to demonstrate nitrogenase activity in situ over short periods by incubating Spartina alterniflora Loisel. in enclosures with C 2H 2, 8–24 h were required for maximum, stable rates of C 2H 4 production. A pC 2H 2 of 0.1 atm was insufficient to saturate nitrogenase sites, but at higher partial pressures of C 2H 2, inhibitory effects of C 2H 2 on nitrogenase activity were evident. Ethylene produced in the soil appears to be very slow in equilibrating with the gas phase. Rates of C 2H 2 reduction associated with sods placed in closed containers under low pO 2 (“potential nitrogenase activity”) were 1–5 times those observed for the in situ systems. These differences can be largely accounted for by the poorer gas exchange in the in situ systems.