Photosynthesis is is the primary process of energy acquisition in higher
plants. Without
photosynthesis, life on Earth would be inconceivable. Anyone with knowledge gaps concerning
photosynthesis should fill these in through self-study.
Light is electromagnetic radiation. The part perceived by the human eye
lies in a wavelength range
between 400 and 760 nm. Light influences plant growth and substance production through:
- Light quantity and light intensity
incident on the photosynthetic organ (which in turn depends
on direct or diffuse solar radiation, and canopy density).
- Temporal distribution, i.e., day
length, which among other things influences the duration of
vegetative growth and the transition to the generative phase.
Long-day plants:
The generative phase is accelerated by long, uninterrupted illumination;
shortening the daily light period (= falling below a critical day length) delays flowering (e.g.,
spinach, head lettuce, cereals).
Short-day plants:
The generative phase is initiated with a relatively short daily light phase;
long illumination (= exceeding a critical day length) delays flower induction (e.g., rice,
poinsettia, chrysanthemum).
Day-neutral plants
(e.g., maize, tobacco).
- Wavelength ranges of light have different
effects. Wavelengths in the:
Violet range are
responsible for phototropism (e.g., bending of the shoot towards light).
Blue range are responsible
for photomorphogenesis (higher blue proportion => more
compact growth, darker leaf color; sun leaves are smaller and thicker than shade leaves).
Red range (P660 – far-red, inactive <=> P730 – red, active) are responsible for initiating
developmental processes (e.g., germination, flowering, pigment formation).
Green-red range
is responsible for photosynthesis (Photosystem I and II)
