Nitrogen fixation as a control in the nitrogen cycle

Abstract

The N cycle is a quickly turning process determining the growth rate of N limited organisms. To maintain a stable standing crop in N limited systems, the N cycle must be controlled so that biomass neither increases indefinitely nor decreases to extinction. A model of the N cycle involved in the growth of very productive N limited seagrass was constructed to analyze control features. Experiments were performed on the model to determine which ecosystem N source (detritus decay, animal excretion, or N fixation) could control the N cycle. It was concluded that N fixation acts as a control in the seagrass growth N cycle because N fixation is induced by low levels of fixed N to increase ambient N concentrations and thus return the system to equilibrium. It is suggested that N cycle control by N fixation is responsible for the enormous production of some N limited plants. © 1985 Academic Press Inc. (London) Ltd.