Far-Red Light Affects Stomatal Opening and Evapotranspiration of Sweet Basil

Abstract

Far-red light (FR; wavelength: 700–800 nm) is known for its effects on plant morphology and photosynthesis. However, its effects on stomatal responses and transpiration are not well understood. This study investigated the effects of FR on stomatal development and evapotranspiration in sweet basil grown under red, blue, and green (RGB) light-emitting diodes (LED). FR was provided for 10 days at 0, 30, 100, and 130 μmol·m−2·s−1 with the same base light (RGB ratio of 6:2:2; a photosynthetic photon flux density of 200 μmol·m−2·s−1). Evapotranspiration was measured using a load cell, and stomatal development was monitored microscopically. FR increased the height of sweet basil mostly due to the shade avoidance syndrome. The photosynthetic rate was not improved with FR, probably due to insufficient base light intensity. Despite similar leaf area and root growth, daily evapotranspiration increased with FR, resulting in higher water use. Although the stomatal density and guard cell area were similar across treatments, the stomatal aperture area was larger in plants with FR, thus increasing evapotranspiration. In conclusion, FR with the base RGB light intensity of 200 μmol·m−2·s−1 enhanced the evapotranspiration of sweet basil by regulating stomatal opening, but it did not enhance photosynthesis.