Light Requirements for Germination and Early Development of Cork Oak under Natural, Semi-Natural and Artificial Conditions

Abstract

Plant factories are closed growing systems producing high-quality vegetables during the whole year, due to an artificial control of the cultivation environment (i.e. light intensity, photoperiod, temperature, carbon dioxide concentration, relative air humidity, culture substrata). Presently, no plant factories producing forest species are available. The first European project focusing on this topic was the European project Zephyr, started in 2012 and concluded in 2016. For each of the species to be cultivated the most suitable values of temperature, relative air humidity, photoperiod and light quality have to be selected according to data from literature and field surveys. While the optimal values of the former three above mentioned parameters for a target species are easily achievable, the definition of the best quali-quantitative light conditions for its growth is a challenging hint. In this work, specific light needs, in terms of photoperiod, light quantity and quality, for seed germination and seedling development of cork oak have been studied. To reproduce optimal light conditions in a controlled environment, these parameters were analyzed in a nursery and in a greenhouse, and, for comparison, in a mature cork forest in Central Italy (Viterbo). Germination resulted to occur both in sunny and shaded areas. Clouds effect was analyzed in an open area showing a significant reduction of light intensity (up to 90 %) without great variations in light quality. Commercial lights provide spectra which are quite different from the spectrum of the sun, especially for higher values of PAR. To evaluate the effects of different spectra on germination and seedling development, 7 light sources were tested for cork oak propagation with a photoperiod of 12L 12D. Data were compared to those collected into the forest. Germination and seedling development resulted to be speeded up under all artificial conditions. This may be caused by the specific artificial light spectra but, above all, by the constant values of temperature and photoperiod that modify radically the plant phenology.