Effects of increasing CO2 concentration and leaf temperature on the photosynthesis of
Bahiagrass (Paspalum notatum Flugge)


1. Introduction
  In general, rising CO2 concentrations increase the productivity of C3 plants by direct CO2 enrichment; the effect on C4 plants is less than that on C3 plants. It is still necessary to evaluate the effect of changes in CO2 concentration for each grass species, in order to forecast the change in productivity of many grass species expected to accompany climatic change.
  Bahiagrass is one of the tropical grasses cultivated in Japan. We measured the effect of doubling CO2 concentration on the net photosynthesis of Bahiagrass leaves.


2. Results
fig1
Net photosynthesis versus PPFD (incident photosynthetic photon flux densities) for a CO2 concentration of 350 ppm.

fig2
Net photosynthesis versus PPFD with each leaf temperature for a CO2 concentration of 700 ppm.

  The net photosynthesis increases at a decreasing rate with PPFD. It also increases with elevation of leaf temperature. Comparing the two figures, for a given leaf temperature the net photosynthesis is proportional to the CO2 concentration.
  At a CO2 concentration of 350 ppm, net photosynthesis of 40 Celcium degree indicates nearly same value as that of 35 Celcium degree at each PPFD. On the other hand, at a CO2 concentration of 700 ppm, the value of net photosynthesis at 40 Celcium degree was greater than that at 35 Celcium degree. It is clear that the increase in CO2 concentration increased the photosynthesis and extended the range of optimum temperatures. Therefore, CO2 concentration rather than leaf temperature was hypothesized to limit the photosynthetic ability of bahiagrass at high temperatures under current climatic conditions.
  The effect of the increase in CO2 concentration on the relative photosynthetic ratios was calculated for each temperature. The results show that the relative ratio increases with rising leaf temperatures.

fig3
The relationship between leaf temperature and relative photosynthetic ratio.

  According to this equation, when the CO2 concentration rises, an increase in leaf temperature further elevates the net photosynthesis of bahiagrass.
  In conclusion, both of the parameters expected to increase with global warming,


REFERENCES
SASAKI,H, M.FUKUYAMA, T.SUYAMA, T.ONOUE and A.SHOJI(1998)
Photosynthesis of bahiagrass (Paspalum notatum Flugge) in a high concentration of CO2.Grassland Science 44(1),93-95.
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