Plants and Animals as Conservative Climatologists:Photoperiodism

Snowshoe Hare (Lepus americanus)

Snowshoe Hare (Lepus americanus)

Arctic Fox’s Coat Color

MELATONIN: A POTENTIAL NIGHT-SIGNAL

The methoxylated indoleamine hormone, melatonin (5-methoxy N-acetyltryptamine), was originally isolated from the mammalian pinal gland. In animals it is a hormone which regulates both circadian behaviors (e.g. sleepiness) and annual events (e.g. seasonal reproduction).

Melatonin has been called "the chemical expression of Darkness” because it circulates predominately at night.

http://www-plb.ucdavis.edu/labs/oneill/melatonin.html

The flowering response of many plants is controlled by the photoperiod (the length of uninterrupted darkness). Photoperiod response can be divided into three types.

• Short day plants flower in response to long periods of night darkness. Examples include poinsettias,

Christmas cactus, chrysanthemums, and single-crop strawberries.• Long day plants flower in response to short periods of

night darkness. Examples include onions and spinach.• Day neutral plants flower without regard to the length

of the night, but typically flower earlier and more profusely under long daylight regimes. Day neutral strawberries provide summer long harvesting (except during heat extremes).

Poinsettia (Euphorbia pulcherrima)

Soybean (Glycene max)

Development of the soybean plant begins at germination and ends when mature seeds are ready for harvest. All aspects of soybean development including length of vegetative growth, timing of flowering, and maturity date are greatly influence by photoperiod and temperature. Because soybean is highly sensitive to photoperiod soybean varieties are adapted to narrow bands of longitude or maturity classes.

There are thirteen recognized maturity classes for soybean varieties. Varieties adapted to southern latitudes will often grow taller and mature later than normal when planted in northern latitudes. Varieties adapted to northern latitudes will often be shorter and mature earlier than normal when planted in southern latitudes.

Soybean Variety Adaptation

Soybean Variety Adaptation

Echinacea

www.greenhousegrower.com/magazine/?storyid=1499

Flowering of some Echinacea cultivars has been reported to hasten following a cooling treatment, also known as vernalization. We tested the response of ‘Sunrise’ to a 15-week vernalization treatment at 41°F. Following cooling, plants flowered under long-day (16-hour) or short-day (nine-hour) photoperiods. However, under short days, flowering was delayed by four to five weeks and plants were shorter and had fewer buds compared with plants under long days.

Non-cooled echinaceas flower only under long-day photoperiods and rosette under short-day photoperiods. When ‘Sunrise’ was grown under a nine-, 12-, 13-, 14- or 16-hour photoperiod, plants flowered only when the photoperiod exceeded 13 hours (Figure 2).

Photoperiodism in Corn (Zea mays ssp mays) and Teosinte (Zea mays ssp parviglumis)

Teosinte in the growth chamber (12 hr light; 12 hr dark),6 weeks after planting.

Teosinte in Missouri (long day environment), 4 months after planting.

How will plants and animals that are adapted to photoperiod be affected by global warming?