Air current around single leaves and plant canopies and its effect on transpiration, photosynthesis, and plant organ temperatures

Abstract

Carbon dioxide (CO2) and water vapor exchanges between plants and the atmosphere are regulated by resistance to gas diffusion from the atmosphere to the chloroplast for CO2 diffusion (photosynthesis) and from the stomatal cavity to the atmosphere for water vapor diffusion (transpiration). Photosynthesis and transpiration are commonly controlled by stomatal and boundary layer resistances. Several environmental factors have been reported to affect photosynthesis and transpiration through the stomatal aperture. In the present chapter, the boundary layer resistance as affected by air movement is focused, and the effects of air current speeds lower than 1 m s-1 on net photosynthetic (Pn) and transpiration (Tr) rates of single leaves and plant seedling canopies through the boundary layer were mainly assessed. The Pn and Tr of leaves doubled as air current speeds increased from 0.01 to 0.3 m s-1 and were almost constant at air current speeds of 0.4-1.0 m s-1. The increase in Pn and Tr was greater in the plant canopy than in the single leaf. Air movement is also important to ensure that the environmental variables remain uniform inside the plant canopy. Controlled air movement is important for enhancing the gas exchange between plants and the ambient air and is consequently important for promoting plant growth especially in semi-closed plant production facilities.