RAPID REGULATION OF LEAF PHOTOSYNTHESIS TO MAINTAIN GROWTH IN IRREGULAR LIGHT ENVIRONMENTS

Protected plant productions in northern latitudes rely heavily on supplemental light use to extend the number of light hours during the day. To conserve electricity and lower costs, a low-energy input system uses supplemental lights preferable during less expensive off-peak hours and turn lighting off during peak load periods in the afternoon and in the morning. This system, though more cost-effective than conventional lighting methods, creates irregular lighting patterns of natural sunlight interrupted with supplemental lighting. Despite being disturbed in their circadian activity, plants grown in such irregular light environments exhibit growth rates linearly related to the daily light integral (DLI). This contradicts with the assumption that plants perform better with a circadian clock matching the environmental clock and suggest that plants are able to buffer their circadian activity in order to maintain carbohydrate status and growth in unpredictable light environments. Our recent results show rapid regulation of photosynthesis and leaf carbohydrate status to maintain growth and light interception in dynamic light environments when campanula, rose and chrysanthemum were grown in a cost-efficient light control system. Plant dry matter production was in all cases linear related to DLI, despite changes in daily light duration and light intensity of supplemental light suggesting that DLI is the main limiting factor for the prediction of production time in optimal temperature conditions.