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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 2 ase 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 2 ase activities.

Observations on the growth habit of a thatch island Spartina alterniflora colony in Nova Scotia indicated that an individual shoot clump lives for 2 years and then dies. There were three distinct phases of growth during the year: rapid leaf and root growth in June and July, vigorous rhizome growth and production of overwintering tillers concurrent with reproductive development in August and September, and finally, a period of no obvious change from October until the following May. There was a distinct autumn accumulation of non-structural carbohydrates in underground parts, with sugars accounting for 31% of the dry weight in October and starch 4%. Ratios of functional belonground biomass to end of season aboveground biomass were roughly constant for stands more than 1 year old; the ratio of annual net production of belowground parts to end of season aboveground biomass was estimated as 1·75.