Kazutoshi Yabuki

Studies on the carbon dioxide enrichment for plant growth, VII. Changes in dry matter production and photosynthetic rate of cucumber during carbon dioxide enrichment

Abstract The dry matter production and the rate of photosynthesis of cucumber under CO2-enrichment were measured. The effect of CO2-enrichment on the growth was great at 1,200 ppm and 2,400 ppm with the growth of 1.5–1.8 times greater than that of the control plot. The effect of 5,500 ppm enrichment, however, decreased with the duration of enrichment. The most effective CO2 concentration for the growth varied from the higher to the lower concentration as the enrichment continued. This was because the effect of enrichment on the growth rate changed with the duration. The CO2-enrichment was effective on the rate of net photosynthesis of cucumber leaves at the beginning. As the enrichment continued, however, the rates at the higher CO2 concentrations rapidly decreased to below that at the normal CO2 concentration. The decrement in net photosynthetic rate was greater when the concentration was higher and the duration of enrichment was longer. The reduction in the effect of enrichment on photosynthetic rate during enrichment accounted for the change in the most effective concentration on the growth rate with the duration.

Photosynthetic Rate of a Plant Community and Wind Speed

The previous chapter illustrated not only that wind speed affects the photosynthetic rate, but also that its effects are different from those of other environmental factors. Of course, it is conceivable that the photosynthetic rate of a plant community, a cluster of single leaves, may be affected by the wind speed. Thus, to uncover facts about the photosynthetic rates of plant communities in nature, we measured the rates of several types of vegetation.

Gas Exchange between the Pneumatophores and Roots of Mangroves by Photosynthesis of Pneumatophore

Mangroves are a generic name for certain tropical or subtropical shrubs and trees that grow along brackish tidal estuaries. It is said that there are approx. 110 species of mangroves throughout the world.

Photosynthetic Rate in the Aspects of the Leaf Boundary Layer

In the previous chapter, I introduced the concept of leaf boundary layer resistance into the CO2 diffusive resistance theory as to the photosynthetic rate. Examining the details of the layer, I then explained that the layer is changed in shape by various factors including wind speed, wind direction, and leaf vibration. But I also explained that the layer’s diffusive resistance value fluctuates along with changes in leaf shape. These facts mean that the CO2 diffusion rate, or photosynthetic rate, also varies with such changes. This chapter discusses the relationship between photosynthetic rate and the variation of leaf boundary layer resistance value associated with environmental changes.

CO2 Exchange between the Air and the Leaf

Chloroplasts in the leaf exposed to light perform photosynthetic reactions. The reactions induce a reduction in CO2 concentration within the chloroplasts, and create a difference in concentration between them and the air, allowing atmospheric CO2 to diffuse into the leaf. As described above, such a diffusion of CO2 occurs through various organs with physically or chemically different functions. Each of them acts as a resistance to CO2 diffusion. Therefore, the rate of CO2 diffusion, or photosynthetic rate, can be calculated from the difference in CO2 concentration between the air and the chloroplasts, and the resistance values of these resistors. Such diffusive resistance values, of course, vary with the environmental conditions surrounding the leaf. This idea, as already mentioned, is called the “diffusive resistance theory.” Brown and Escombe (1900), who both advanced this theory, assumed that aconical air layer over the stomata and the endostomata each acted as a resistance in series coupling.

A Closer Look at Wind

Agriculture is fundamentally a technique of converting a natural ecosystem through environmental control, in a broad sense, into a farmland ecosystem for food production. Though related to this technique, my major field, environmental control in agricultural engineering, covers some aspects of agricultural physics. Because of this, I was involved in research projects that did not have a direct link to crops, such as “Raindrop Energy and Soil Erosion,” “Heat Balance of Paddy Fields and Methods of Increasing Water Temperature,” “Causes of Airflow over Mountains,” and “Environmental Control of Greenhouses.” However, in 1960, 15 years after I started treading the path of agricultural science, a consecutive shift in thinking occurred to me during my stay at the Physics Department at Rothamsted Experiment Station in England.