Nitrogenase activity in relation to season, carbohydrates and organic acids in a temperate zone root association

Nitrogenase activity associated with grasses is commonly reported to be maximal during reproductive growth. For Spartina alterniflora, a perennial grass growing in salt marshes, seasonal changes in potential (excised root) N 2ase activity followed, by about 2 weeks, seasonal changes in ethanol soluble carbohydrate concentrations in roots and rhizomes. Both varied by about 3-fold during the year, declined rapidly with the onset of vegetative growth, and increased to previous levels during reproductive growth. N 2-ase activity measured on intact systems in situ was also maximal during reproductive growth, but the absolute rates were much lower than the potential N 2ase activities.