Water and Crop Production

I. The relationship between photosynthesis and transpiration in corn leaf

Abstract

In order to clarify the relationship between photosynthesis and transpiration in corn leaf, the responses of photosynthetic rate, transpiration rate and water vapour transfer coefficient (D) to light intensity, leaf-air vapour pressure difference (leaf-air VPD) and leaf water content were measured by means of the chamber method. The assimilation chamber was designed to be controllable independently environmental factors such as light intensity, temperature, humidity and wind speed. The results obtained were summarized as follows;
1. The responses of photosynthesis, transpiration and D to light intensity were shown almost the same pattern when leaf temperature, leaf-air VPD and wind speed were maintained constant (Fig.3).
2. When only leaf-air VPD was changed under constant conditions of other factors, the relationship between photosynthesis and transpiration showed two types, namely negative and no correlations (Fig.5).
3. When only leaf water content was changed by means of detaching leaf blade from plant under constant environmental condition, the responses of photosynthesis, transpiration and D to leaf water content were shown almost the same trend (Fig.7).
4. Through analysing the results shown in 1, 2, 3 the relationships between photosynthesis and transpiration were summarized as follows; (1) When transpiration was directly proportional to D, it was positively correlated with photosynthesis. (2) When transpiration was inversely proportional to D, it was negatively correlated with photosynthesis. (3) And when transpiration had no relation to D, it had no correlation with photosynthesis (Fig.9).
5. From the results mentioned above, it was concluded that photosynthesis was rather affected directly by D than transpiration (Fig.10).