Light Stress

1
Light Stress

• Light quantity
• Energy budget consideration
• Sin Lin Sout Lout C ET Ps DH
• Photosynthetic photon flux density (PPFD)
• Light to drive photosynthesis
• Excess light fluorescence and photo-oxidation
• Light quality
• R/FR ratio (phytochrome system)
• UV

2
Light Stress Definition of C
From energy balance equation (C) conduction and
convection - turbulent diffusive transfer of
energy from leaf surface to bulk air ( bulk air
to leaf). Two parts 1. Laminar or diffusive
layer around a leaf, a group of leaves or
the canopy is frequently referred to as the
boundary layer. 2. In contrast, a turbulent layer
is well mixed movement of gas, heat,
momentum is rapid. 3. A leaf whole boundary layer
is constantly being replaced is said to be
well coupled to the atmosphere. 4. A leaf with a
thick, stagnant boundary layer is said to be
decoupled. 5. Geometry of the leaf and wind speed
have major influences on the boundary layer
stomatal opening has a minor influence on
the boundary layer.
3
Light Stress Basic Plant Strategy

• At high light levels, increase maximum fixation
  rates and spread light out over more leaves to
  minimize saturation.
• At low light levels, collect as much light as
  possible with the minimum investment in tissue
  and enzymes

PPFD
4
Light Results from Lab
5
Light Results cont.
6
Light Stress