This study was carried out to elucidate the effect of environmental factors such as light intensity, temperature, soil water content, and nutrients on photosynthesis of Oenanthe stolonifera.
The results are summarized as follows;
1. Plants grown at full sunlight showed light compensation point of 2.3klux and light saturation point of 60klux. These parameters showed a tendency to decrease with decrease in light intensity during plant growth.
2. Dark respiration rate increased with temperature increase, and maximum photosynthetic rate appeared at 25℃ under high light intensity above 30klux. Decrease in net photosynthetic rate at high temperatures was associated with a rapid increase in respiration.
3. Maximum photosynthetic rate was observed at high temperatures with high light intensities, and at low temperatures with low light intensities.
4. Optimum temperature for net photosynthesis tended to decrease with decrease in light intensity during plant growth.
5. As the soil water content decreased, the net photosynthetic rate decreased. Especially, the rapid decrease of photosynthetic rate appeared at the initial wilting period.
6. N, K, and Mg were very important for photosynthetic rate of O. stolonifera, with Mg being the most important factor. The maximum photosynthetic rate was observed at full strength under 20℃ and 50klux, whereas it also was observed at 1/2 or 1/4 of full strength under 10℃ and 9klux.
7. Chlorophyll contents were increased with decrease in light intensity and the leaves grown at 25% of full sunlight had chlorophyll twice as much as those at full sunlight. No difference in chlorophyll a/b ratio was found among the control and shading treatments with the values being around 3.0.
8. Electron microscope observation of chloroplast sections indicated that the number of thylakoids per granum increased rapidly with decrease in light intensity during plant growth.
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