Signify LED greenhouse lighting alters transpiration and tip burn
LED lighting changes greenhouse microclimates and calcium transport, increasing tip burn risk. Learn the strategies to improve crop performance in your operation.
Greenhouse growers transitioning from high-pressure sodium lighting to LED systems may need to adjust climate and heating strategies to prevent tip burn, according to trial results from Lepaa, Finland.
Research conducted by Signify, Häme University of Applied Sciences and Aranet found that calcium did not effectively reach the plant head under a hybrid lighting system, even though water uptake remained steady. The crop was grown under a photosynthetic photon flux density of 460 µmol/m²/s using a lighting mix of 75% LEDs and 25% HPS.
Tip burn, commonly linked to calcium deficiency, is often caused by disrupted calcium transport. Because calcium moves passively with water, its delivery depends on transpiration and sap flow. Sensors attached to leaf petioles showed that while plants absorbed water throughout winter, sap flow in upper leaves slowed as relative humidity increased in the canopy, reducing evaporation and calcium movement.
Tomato leaves in September, November and December. Each leaf is the 8th leaf counted from the top of the plant. Despite steady water uptake, the calcium fails to reach the plant head.
Data also showed that when HPS lights were switched off, sap flow in upper leaves dropped sharply, while lower leaves were unaffected. In LED-dominant systems, cooler leaf temperatures and reduced air movement in the upper canopy further limit transpiration compared with HPS systems, which emit radiant heat that promotes air circulation.
Sap flow rate on the 12 th of November measured from a leaf in the upper canopy (orange) and lower canopy (green). Lights were switched on at 5:20. HPS 140 µmol/m2/s was switched off 19:20, and LED toplighting 240 µmol/m2/2 were switched off at 20:40.
Researchers observed that nighttime heating from rail pipes caused lower leaves to transpire continuously, diverting water away from the plant head. Allowing slightly higher humidity at night and lowering pipe temperatures can help stomata close, restoring root pressure and improving calcium movement.
By adjusting screen use, pipe placement and air circulation, growers can reduce microclimate imbalances that contribute to tip burn in LED-lit greenhouses.
Photo courtesy of Signify.