Effect of supplemental far-red light with blue and red LED lamps on leaf photosynthesis, stomatal regulation and plant development of protected cultivated tomato

In order to solve the problems of light insufficiency that occur in intensive greenhouse production, we applied far-red-wavelength introduced light-emitting diodes (LEDs) as supplemental lighting to the lower canopy of intensively cultivated tomato. To test the performance of this light source, we measured leaf photosynthesis, stomatal regulation, and plant development of tomato treated with or without supplemental lighting of deep red/blue (DR/B) and deep red/blue/far-red (DR/B/FR) LEDs. Leaf photosynthesis rate (P(n)), transpiration rate (T(r)) and stomatal conductance (G(s)) increased significantly in plants treated with both supplemental lighting regimes, and the enhancement in the DR/B/FR treatment was greater than that in DR/B. Stomatal closure was reduced with treatment of supplemental lighting, while DR/B/FR introduced a larger stomatal pore area, stomatal density, and stomatal index compared with DR/B. Relative growth rate (RGR) and net assimilation rate (NAR) of plants treated with DR/B/FR were significantly higher, while the leaf area ratio (LAR) was higher in DR/B treatment. Though stem height decreased, plant dry weight and flower number were significantly increased by the application of supplemental lighting. Investigation of interspecific relationships between metabolism and morphology showed that P(n), G(s), RGR, NAR, stomatal pore area, root length and weight were all highly correlated (R(2)≈0.9), suggesting a close coupling of organ-level metabolism and whole-plant performance. These results reconfirmed the effectiveness on plant growth of supplemental lighting to cope with light insufficiency, and indicated that the introduced far-red- to red and blue-wavelength irradiation could intervene to prevent stomatal closure and promote root development to guarantee leaf photosynthesis and dry matter production, therefore enhancing plant growth and development under low light conditions.