Effects of short daily periods of interlighting on leaf acclimation to light conditions in a Cucumis S. canopy.

MSc-thesis abstract (submitted 23 June 2016): Application of assimilation light within the canopy (interlighting) by Light Emitting Diodes (LED) might increase the Light Use Efficiency (LUE) of assimilation light inputs via acclimation of interlighted leaves to higher light conditions.
The aim of this study was to trigger leaves to acclimate to high light conditions in a Cucumis S. canopy by application of only 3.5 or 6 hours of daily intensive LED interlighting without additional top-lighting.

Similar sums of interlighting (x hours day-1) were applied on a fixed set of fully developed leaves at a fixed height, either during mid-day (Mid-day interlighting) or during the early morning and late evening (Sunset-sunrise interlighting).

Leaf morphology, nitrogen- and chlorophyll distribution within the canopy and photosynthetic characteristics were measured at leaf level. Additionally, stomatal conductance (gs) and dynamics in sap flow rate trough petioles of interlighted leaves were measured. Crop productivity, including fruit yield and total dry matter production, were examined.

Neither MDI nor SSI triggered long-term acclimation of leaves to high light conditions and no effect was observed on crop productivity.
On the short-term, inter-lighted leaves increase their gs while sap flow dynamics correlated with incident radiation levels on the leaves.

Parameters observed in this study show differences between the two experiments conducted, showing the importance of natural outside radiation levels on leaf acclimation parameters and distribution of resources in the canopy.

Although results of this study may not be directly applicable for practice, as the experiments were conducted without additional top-lighting.