Temperature affects the ratio of ethylene produced to N2-fixed more than immediate release of fixed N in streams

Nitrogen fixation across the aquascape: current perspectives, future priorities

“…N 2 fixation rates measured in one year at this site show that rates can be exceptionally high during the peak of the bloom formation, although the blooms are short-lived and subside with the end of the growing season in this strongly seasonal, montane river. This study joins a growing body of literature demonstrating that lownutrient, high-light streams can host benthic cyanobacteria that can fix at very high rates for short periods of time when temperature and nutrient conditions are favorable (e.g., Grimm and Petrone 1997;Kunza and Hall 2023). Further, these ephemeral contributions may be important for supporting productivity and ecological assemblages in these habitats at key times and places.…”

“…However, a major drawback is that the proportion of ethylene produced to ammonium fixed tends to vary across diazotrophic species and the environments in which they inhabit and many studies do not include study specific conversion factors. Kunza and Hall (2023) test the variability in acetylene reduction compared with 15 N 2 labeled water in benthic biofilms and Nostoc populations in four Wyoming streams. They found that the ratio of ethylene to ammonium produced in their assays varied substantially, and that ethylene production increased almost 2 times faster than 15 N 2 uptake as stream water temperature increased, providing the potential for temperature to bias N 2 fixation rates determined using ARA.…”