Fotoperiodism

Fotoperiodism, also known as photoperiodism, is the physiological response of organisms to the length of day or night. In plants, it regulates seasonal processes such as flowering, dormancy, and tuber formation; in animals, it influences reproductive timing, migration, and diapause.

In plants, light information is perceived by photoreceptors such as phytochromes (red/far-red light) and, in some species, cryptochromes. These signals interact with the plant’s circadian clock to determine whether a given day length triggers a flowering response. A central concept is the critical photoperiod—the day length that elicits a reaction. Long-day plants flower when days exceed this threshold, short-day plants flower when days are shorter than it, and day-neutral plants show flowering relatively independent of day length.

In animals, photoperiod is conveyed mainly by melatonin produced by the pineal gland in response to night length. Melatonin signals influence the timing of reproduction and other seasonal biology through the hypothalamic–pituitary–gonadal axis, as well as diapause, molt, or migration in some species. Different species can respond in opposite directions to the same photoperiod.

Applications and implications of photoperiodism include agricultural scheduling, such as manipulating flowering and dormancy in crops and bulbs. It also shapes wildlife ecology and conservation, and remains a focus in studies of climate change, as shifting light cues can alter seasonal timing and synchronization with the environment.

Historically, photoperiodism emerged from early 20th-century work showing that day length controls flowering and physiology, with models linking circadian clocks to light perception.