Agriculture Reference
In-Depth Information
Fig. 6.12
Two leaves with differences in the chlorophyll content and hence also in the photosynthetic
activity, the absorbance and the reflectance of photochemically active radiation. But there are also
principal differences in the fluorescence and in the heat loss
Table 6.1
Use of absorbed light quanta
a
Energy used for …
Optimal photosynthesis (%)
Blocked photosynthesis (%)
Photosynthesis
84
0
Heat loss
14
88
Chlor. fluorescence
2
12
a
Compiled from data by Rosema et al. (
1991
)
Actually, plants are not wasting much of the solar energy that they receive if the
growing conditions are good and the leaves are well equipped with chlorophyll. But
the situation is quite different if photosynthesis is impeded or cannot take place at
all though sufficient photosynthetic active radiation is available. For growing crops
such situations can
e. g.
result from the lack or from a wrong supply of water or
mineral nutrients. Diseases or pest infestations too can cause this. Hence plants
need means to get rid of all or part of the solar energy if photosynthesis cannot take
place. The dissipation of chlorophyll fluorescence and simply of heat to the environ-
ment serves this purpose (Fig.
6.12
).
It seems reasonable to relate the thus dissipated energy to the energy of the
absorbed light (Table
6.1
). When the growing conditions are optimal, only 2 % of
the absorbed energy is emitted as chlorophyll fluorescence. If on the other hand the
