Fig. 4

Relative spectral photon distribution (SPD) data acquired under different foliar shade sites representing moderate and deep spectral motifs in St. Paul MN during 2018 and 2020. A Full sun, B Maple grove-southern row, C Oak grove, D Northern forest edge, E Southern forest edge, F Maple grove-northern row, G Within a forest, H Under a wheat canopy, I Under a barely canopy in a greenhouse, and J Under a canola canopy in a greenhouse. Data were normalized to the photon flux at 800 nm and are presented as the average of relative SPDs acquired on 28 May, 13 June, 2 July, and 6 July for 2018 (A–E, G), 30 May, 31 May, 12 June, and 11 Aug. 2020 (F), 2 and 6 July 2018 (H), and 23 April 2018 (I, J). The average relative PPF of blue (B), green (G), and red (R) light are inset in each panel (see Additional file 2: Table S1 for sample statistics); the average R:FR (655–665 nm/725–735 nm) and B:G (420–490 nm/500–570 nm) ratios are inset in each panel. Data were acquired between 13:00 and 14:00 h on clear sky or mostly sunny days only. Red bars indicate 400 and 700 nm, respectively, designating photosynthetically active radiation (PAR) between the red bars