Photoperiodism

Definition

The response of plants (and some animals) to the relative lengths of day and night, which controls processes such as flowering.

Key points

• Plants are grouped by their flowering response: short-day plants flower when the daylight is shorter than a critical length (rice, soybean, chrysanthemum), and long-day plants flower when daylight is longer than a critical length (wheat, barley, spinach).
• Day-neutral plants flower regardless of day length (tomato, cucumber, maize).
• It is actually the length of the continuous dark period, not the light period, that the plant measures; interrupting the night with a flash of light can prevent short-day plants from flowering.
• The pigment phytochrome senses red and far-red light and acts as the plant's clock for measuring day length.
• Photoperiodism also influences seed germination, leaf fall, and, in animals, breeding and migration timing.

Why it matters for CAPF

The short-day, long-day, and day-neutral classification with crop examples, and the fact that plants measure night length, are standard botany facts linked to agriculture and cropping seasons.

Common confusion

Short-day plants actually need a long uninterrupted night, so the controlling factor is the dark period, not the light period; the names are about day length only by convention. Day-neutral plants flower independent of day length, so not every plant responds to photoperiod.

Related concepts

concept photosynthesis, concept cropping seasons, concept enzymes

Parent note

biology cell and classification