1. Photoperiodism in plants

2. Photoperiodism in plants
Photoperiodism – the regulation of seasonal activity by daylength (photoperiod).

3. Photoperiodism in plants
Photoperiodism – the regulation of seasonal activity by daylength (photoperiod).
Long-day plants (LDP):
Only flower when the photoperiod exceeds a certain value, known as critical day length (CDL).

4. Photoperiodism in plants
Photoperiodism – the regulation of seasonal activity by daylength (photoperiod).
Long-day plants (LDP):
Only flower when the photoperiod exceeds a certain value, known as critical day length (CDL).
Does not have to be longer than 12 hours.

5. Photoperiodism in plants
Photoperiodism – the regulation of seasonal activity by daylength (photoperiod).
Long-day plants (LDP):
Only flower when the photoperiod exceeds a certain value, known as critical day length (CDL).
Does not have to be longer than 12 hours.
Characteristic of higher altitudes, where seasonal variation in daylength is greater.

6. Photoperiodism in plants
Photoperiodism – the regulation of seasonal activity by daylength (photoperiod).
Long-day plants (LDP):
Only flower when the photoperiod exceeds a certain value, known as critical day length (CDL).
Does not have to be longer than 12 hours.
Characteristic of higher altitudes, where seasonal variation in daylength is greater.
LDP’s begin to flower when the days are lengthening, in spring and early summer – if transplanted to the tropics, it may not flower because the days aren’t long enough.

7. Photoperiodism in plants
Photoperiodism – the regulation of seasonal activity by daylength (photoperiod).
Long-day plants (LDP):
Only flower when the photoperiod exceeds a certain value, known as critical day length (CDL).
Does not have to be longer than 12 hours.
Characteristic of higher altitudes, where seasonal variation in daylength is greater.
LDP’s begin to flower when the days are lengthening, in spring and early summer – if transplanted to the tropics, it may not flower because the days aren’t long enough.
EG – Temperate grasses, snapdragons, radish and lettuce

8. Photoperiodism in plants
Short-day plants (SDP)
Only flower when the photoperiod is less than the CDL.

9. Photoperiodism in plants
Short-day plants (SDP)
Only flower when the photoperiod is less than the CDL.
Many native tropical species are SDP’s even though the daylength may not vary more than two hours during the year.

10. Photoperiodism in plants
Short-day plants (SDP)
Only flower when the photoperiod is less than the CDL.
Many native tropical species are SDP’s even though the daylength may not vary more than two hours during the year.
EG – Maize and sugar cane.

11. Photoperiodism in plants
Short-day plants (SDP)
Only flower when the photoperiod is less than the CDL.
Many native tropical species are SDP’s even though the daylength may not vary more than two hours during the year.
EG – Maize and sugar cane.
Day-neutral plants
Are not affected by photoperiod
EG – dandelion, tomato, and garden pea.

12. Photoperiodism in plants
Short-day plants (SDP)
Only flower when the photoperiod is less than the CDL.
Many native tropical species are SDP’s even though the daylength may not vary more than two hours during the year.
EG – Maize and sugar cane.
Day-neutral plants
Are not affected by photoperiod
EG – dandelion, tomato, and garden pea.
** Over-simplification. Photoperiod can be affected by plant age, temp and nutrient availability.