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Research article2017Peer reviewed

Ornamental flowers in new light: Artificial lighting shapes the microbial phyllosphere community structure of greenhouse grown sunflowers (Helianthus annuus L.)

Alsanius, Beatrix W.; Bergstrand, Karl-Johan; Hartmann, Rahel; Gharaie, Samareh; Wohanka, Walter; Dorais, Martine; Rosberg, Anna Karin


Artificial assimilation lighting is a common practice in greenhouse horticulture in the circumpolar region to compensate for natural low light conditions. To modulate plant architecture, regulate flowering of photoperiodic crops, increase plant performance per energy input and consequently profitability, light emitting diodes (LEDs) have been suggested as a powerful tool for ornamental growers in complementary or replacement of conventional lighting such as incandescent, fluorescent and high pressure sodium (HPS) lamps. As LED light differs from HPS lamps with regard to spectral output, light distribution as well as heat emission, the microclimate within the crop stand is affected. In two independent experiments conducted in fall and winter, we therefore compared the effect of two types of LED light (red 660 nm + blue 460 nm LED, 80:20 RB-LED; white LED, W-LED) with HPS lighting on ornamental sunflowers (Helianthus annuus cv. 'Teddy Bear'). Depending of the solar radiation (fall vs winter experiments), a same PPFD of 70-120 mu mol m(-2) s(-1) of artificial lighting (photoperiod of 16 h) was given at the top of the plants. Plant growth performance and biomass, leaf temperature, photobiological parameters (photosynthetic activity, stomatal conductance, chlorophyll fluorescence) as well as the leaf associated microbiome, assessed using culture dependent and independent methods on apical, directly exposed to the light treatments, and basal leaves, were studied. As expected, significant differences were obtained for plant related parameters between the two repetitions of the experiment due to difference in solar radiation. Light treatments influenced plant growth performance which was lower for all parameters in sunflowers exposed to LEDs than HPS. However, no differences were found with respect to photobiological parameters. Top leaf temperature was higher in the presence of HPS than LEDs, which explained the lower plant growth performance observed under LED regimes. Colony-forming units representing culturable fungi and fluorescent pseudomonads were higher on basal leaves than on apical ones, but did not vary with respect to light treatments. On the other hand, biodiversity estimated with respect to species abundance and evenness (Shannon-H index) and species richness (Chao1) revealed different patterns for the fungal and bacterial microbiome. Regardless of the leaf position, light treatments affected fungal species abundance and evenness, which was highest on leaves exposed to HPS, but not species richness. The fungal microbiome was more diverse on apical than on basal leaves. For the bacterial microbiome, biodiversity estimates differed between the repetitions. Interactions between leaf temperature and bacterial genera were found for several of the dominant genera in the sunflower phyllosphere (Pseudomonas, Staphylococcus, Enhydro bacter) while other decisive bacterial and fungal genera were correlated to photobiological parameters, e.g. Bradyrhizobium, Sphingomonas, Brevibatericum, Bacillus, Hypotrachyna, Aureobasidium. The use of "new light" in greenhouse ornamentals is not only a technological change modifying plant morphology and development, but also affects the microbial ecology on plant surfaces, implying consequences on plant protection issues and biological control strategies. (C) 2017 Elsevier B.V. All rights reserved.


Assimilation lighting; Leaf temperature; Light emitting diodes; LED; Metagenomic analysis; Microbial community structure; Photosynthetic parameters; Plant growth; Supplemental lighting

Published in

Scientia Horticulturae
2017, Volume: 216, pages: 234-247