Vergara - 1976 - Physiological and morphological adaptability of ri

LTLIMAHC INFLUENCE ON
PHOTOSYbTfHESlS AND RESPIRATION
The net photosynthesis substrating respiration loss is usually less than 5—6%
of the total energy’ absorbed. The efficiency of net energy conversion by a rice
population was about 5% at booting stage. reached a maximum value of 7%
at heading. and showed a rapid decline thereafter. Most of the energy absorbed
was lost by transpiration and heat transfer (Murata et a1. 1968).
The production processes of a plant population depend on many complex
interactions between environmental and biological factors, Light intensity‘ and
productive structure of the plant population are the most important factors
which determine its dry matter production, Monsi and Saeki (1953) found that
light extinction by leaves in the plant population was expressed by the exponential
equation:
I = 1,, exp( — KF) (4)
where I: light intensity beneath a LAI of F. 1,: light intensity“ above the community.
F: LAI above the point of measurement. K: extinction coefficient. K
is calculated by the stratified clipping method where the plant is harvested in
successive shallow layers from the surface downward and accompanied by a
simultaneous record of light profile, K tvas closely correlated with leaf arrangement,
especially" leaf angle. and its value was inversely" related to the leaf angle.
'l'akeda and Kumura (1957) and Murata (1961) indicated that exponential
equation (4) was applicable to rice populations.
Monsi and Saeki (1953) expressed net photosynthesis (q = p — r) per unit
leaf area by the following equation:
q = bl _ _
1+n
' i”
where r indicates respiration per unit leaf area, a and b are coefficients related to
the photosynthetic capacity of a single leaf. By substituting the light intensity
in equation (5) by equation (4) and integrating from 0 to F for LAI. the equation
for total net photosynthesis of population (P) becomes;
P: b m l+amu
a K 1+ a Kloexp(— KP)
— rF (6)
Munakata ct al, (1970) indicated that when the respiration function (r1?)
was represented by Arrhenius equation (3), the photosynthesis in rice population
could be approximated by equation (6).
The light saturation point for photosynthesis in a plant population becomes
higher with increasing leaf area. The light-photosynthesis curve is markedly"
affected by the extinction coefficient as well as by leaf area. The net photosynthesis
of a plant population with vertical foliage was shown to be theoretically
greater than with horizontal foliage at a high leaf-area index, However, at a
low leaf-area index the plant population with horizontally oriented leaves
shtiwed greater photosynthesis (Saeki. 1960).