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How do plants use changing day length to prepare for winter?

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fern life cycle — plant development The life cycle of the fern. (1) Clusters (sori) of sporangia (spore cases) grow on the undersurface of mature fern leaves. (2) Released from its spore case, the haploid spore is carried to the ground, where it germinates into a tiny, usually heart-shaped, gametophyte (gamete-producing structure), anchored to the ground by rhizoids (rootlike projections). (3) Under moist conditions, mature sperm are released from the antheridia and swim to the egg-producing archegonia that have formed on the gametophyte's lower surface. (4) When fertilization occurs, a zygote forms and develops into an embryo within the archegonium. (5) The embryo eventually grows larger than the gametophyte and becomes a sporophyte.

In temperate zones, plants use the shortening of day length as a critical environmental signal to anticipate and prepare for winter, a process known as photoperiodic control. As day length falls below a specific threshold, many plants cease shoot growth and form resting buds to protect their stem apexes from harsh conditions.1

This response is often mediated by the formation of inhibitor compounds. For instance, in birches, leaves perceive the day-length signal and transmit inhibitory materials to the plant's apex, effectively halting growth. While the hormone abscisic acid is associated with this dormancy response, other signaling hormones like auxin and ethylene are more significantly involved in processes such as leaf abscission.1

By utilizing these environmental indicators, plants can undergo necessary physiological and morphological adjustments—such as the loss of leaves in deciduous trees or the dying back of aerial parts in herbaceous plants—to ensure their survival during unfavorable seasons.1