Nitrate, a nonphotic signal for the circadian system.

Recent advances in circadian biology have brought insights into the molecular mechanisms involved in the generation of circadian rhythmicity. However, little is known about the relationship between these molecular oscillators and the organism's temporal adaptation to complex daily environmental changes. We have studied the effects of nutrients on the circadian system of a marine unicellular alga and found that nitrate influences all three canonical properties of circadian rhythmicity: amplitude, phase, and period. The effects of nitrate are part of a complex feedback loop involving both circadian input and output. These new aspects of circadian nutrient metabolism have important implications for our understanding of the ecological significance of circadian programs.