Growth, leaf anatomy, and photosynthesis of cotton ( Gossypium hirsutum  L.) seedlings in response to four light-emitting diodes and high pressure sodium lamp

Light is a critical factor of plant growth and development, particularly in controlled environments. Light-emitting diodes (LEDs) have become a reliable alternative to conventional high pressure sodium (HSP) lamps because they are more efficient and versatile light sources. In contrast to well-known specialized LED light spectrums for vegetables, the appropriate LED lights for crops such as cotton remain unknown. In this growth chamber study, we selected and compared four LED lights with varying percentages (26.44-68.68%) of red light (R, 600-700 nm), combined with other lights, for their effects on growth, leaf anatomy and photosynthesis of cotton seedlings, using HSP as a control. The total photosynthetic photon flux density (PPFD) was 215±2 μ mol/m 2 ·s for all LEDs and HSP. The results showed significant differences in all tested parameters among lights, and the percentage of far red (FR, 701-780 nm) within the range of 3.03-11.86% was positively correlated with plant growth (characterized by leaf number and area, plant height and diameter, and total biomass), palisade layer thickness, photosynthesis rate (Pn) and stomatal conductance (Gs). The ratio of R/FR (4.445-11.497) negatively influenced the growth of cotton seedlings, and blue light (B) suppressed stem elongation but increased palisade cell length, chlorophyll content and Pn. The LED 2 was superior to other LED lights and HSP. It had the highest ratio of FR within the total PPFD (11.86%) and the lowest ratio of R/FR (4.445); LED 2 may therefore be used to replace HPS under controlled environments for the study of cotton at the seedling stage.