Abstract
Supplemental lighting can enhance yield when sunlight is limited, as in winter. As the effect of frequent cloudy or rainy days in other seasons on plant growth and yield remains unclear, we investigated the effect on tomato (Solanum lycopersicum) and compensation by supplemental LED inter-lighting. Plants were grown under 30% shade cloth on 0%, 40%, or 60% of days. Lower leaves were illuminated with red and blue LED inter-lighting modules from right after first anthesis, or not illuminated. Shading during 40% and 60% of days diminished daily light integral (DLI) by 26% and 40%, respectively, and reduced shoot dry weight by 22.0% and 23.3%, yield by 18.5% and 23.3%, and fruit soluble solids content by 12.3% and 9.3%. In contrast, supplemental inter-lighting improved the light distribution within plants and compensated DLI, and maintained similar yield and soluble solids content in both shade treatments as in the control. These results clearly show that supplemental LED inter-lighting could efficiently compensate for a shortage of light for plant growth, photosynthesis and thus yield under the lack of sunshine.
Highlights
Valued globally at 58.2 billion USD, tomato is ranked as the 4th most valuable agricultural commodity or crop after rice, wheat, and soybean [1]
It’s important to understand whether cloud cover and low solar radiation limit carbon uptake, photosynthesis, and crop productivity despite the improvement in carbon gain in terrestrial ecosystems by an increased ratio of diffuse radiation [5]
Since our results show that supplemental LED inter-lighting increased daily light integral (DLI) by 2.8 mol m−2 d−1 in the 40% treatment and 4.2 mol m−2 d−1 in the 60% treatment, the use of LED inter-lighting on cloudy days could supply plants with more than the minimum DLI requirement (Table 1)
Summary
Valued globally at 58.2 billion USD, tomato is ranked as the 4th most valuable agricultural commodity or crop after rice, wheat, and soybean [1]. Economic benefits may accrue from investigating the effects of low solar radiation as a result of cloud cover on productivity of greenhouse tomatoes. In the past 50 years the reduction of solar radiation reaching Earth’s surface globally has averaged 0.51 ± 0.05 W m−2 per year, equivalent to a reduction of 2.7% per decade [4]. It’s important to understand whether cloud cover and low solar radiation limit carbon uptake, photosynthesis, and crop productivity despite the improvement in carbon gain in terrestrial ecosystems by an increased ratio of diffuse radiation [5].
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