Effects of Air Current on Transpiration and Net Photosynthetic Rates of Plants in a Closed Plant Production System

Abstract

The effects of the air current speed less than 1 m s^-1 on transpiration (Tr) and net photosynthetic rates (Pn) of sweetpotato leaves and on a canopy of rice plants were determined using a chamber method and a combination of micro-meteorological and weighing methods, respectively. The effects of vertically downward moving and horizontal air currents on the Tr were also compared using a model plant canopy made from wet papers. The Tr and Pn of sweetpotato leaves were doubled as the air current speed increased from 0.01 to 0.3 m s^-1 and was almost constant at air current speeds 0.3–1.0 m s^-1. The Tr and Pn of the rice plant canopy increased linearly by 2.5 and 2 times, respectively, as the horizontal air current speed increased from 0.01 to 0.8 m s^-1. Horizontal air current speeds above lms^-1 are necessary to obtain maximal Tr and Pn of the canopy. The Tr of the model plant canopy was 2–3 times greater with the vertically downward air current than in the horizontal air current in an air current speed of 0.15–0.3 m s^-1. A vertically downward air current at 0.3 m s” around leaves would be adequate for promoting Tr and Pn and thus plant growth in a closed plant production system.