To investigate the mechanism of yield increase by elevated carbon dioxide (CO 2 ) and fogging in Japanese tomato cultivars (Solanum lycopersicum), total above-ground dry matter (TDM), fraction of dry matter distribution to fruit (FDF), and photosynthetic characteristics were measured in 3 Japanese cultivars grown in elevated CO 2 with fogging and ambient CO 2 without fogging. Fresh fruit yield and TDM were improved by the elevated CO 2 and fogging in the 3 Japanese cultivars. Light use efficiency (LUE) was also increased by the elevated CO 2 and fogging. No significant decrease in FDF was observed by the elevated CO 2 and fogging in 2 Japanese cultivars, 'Asabiyori 10' and 'Junkei Aichi Fast'. Thus, the increase in TDM by higher LUE contributed directly to the yield increase in these 2 cultivars. However, FDF in 'Momotaro York' was decreased significantly by the elevated CO 2 and fogging. Thereby, the yield increase by the elevated CO 2 and fogging was diminished in 'Momotaro York' in spite of the increase in TDM. The number of trusses having immature fruit in 'Momotaro York' under elevated CO 2 and fogging was significantly higher than those of the others, although no increase in the number of trusses having immature fruit was observed in the other 2 cultivars. Although vegetative growth characteristics such as leaf area, LAI, and fresh and dry weights of leaves and stem were increased by the elevated CO 2 and fogging, no negative effects such as a change in lightextinction coefficient and a decrease in maximum photosynthetic rate were observed. The elevated CO 2 and fogging increased the number of harvested fruit but decreased weight per fruit, namely, fruit size, in the 3 cultivars.

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Although air circulators are commonly used in agricultural buildings, it is difficult to evaluate the practical performance of many such air circulators currently available in Japan. This study compares the air circulation performances of six commercial air circulators and demonstrates that the distribution of air velocity generation varied among them. Although the power consumption significantly correlated with the range of air circulation observed, the airflow rate listed in the specifications did not. Therefore, power consumption is a better evaluation indicator for the performance of air circulators under the limitation that exceedingly inefficient products are hardly distinguishable. In addition, the energy efficiency in the usage of air circulators is discussed.

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In the last decade, air circulators have been widely used in greenhouses and high tunnels in Japan. The main purpose of air circulation is to provide uniformity in temperature, humidity level, and carbon dioxide concentration in greenhouse air. In addition, empirical knowledge that air circulation prevents hygrophilous diseases increased among growers, together with the inference that air circulation reduces the fuel consumption required for heating. Although the benefits of air circulation remain uncertain, some empirical evidence has been obtained from horticultural and engineering studies in Japan. In this review, the results of these investigations are summarized on the basis of five aspects: performance indicators for circulators, microclimate uniformity, crop yield, suppression of hygrophilous diseases and possible mechanisms. Practical issues regarding the installation of air circulators for greenhouses and high tunnels are also discussed.