Effects of leaf position on reflectance,transmittance and absorption of red and far‐red light in tomato,Chenopodium album and Amaranthus retroflexus leaves

Leaf optical properties can play an important role in determining the red/far‐red light ratio, a signal of impending competition, in plant canopies. Knowledge of leaf optical properties and factors affecting them is important in understanding of the impacts of red/far‐red ratio in agroecosystems. Effects of leaf position on the plant stem on their optical properties at 660 and 730 nm were studied in tomato and two weeds Chenopodium album and Amaranthus retroflexus. Leaf position on stem strongly influenced leaf optical properties. Reflectance and transmittance were generally lower for the C. album and A. retroflexus leaves at higher positions on the stem, except for reflectance at 730 nm in C. album, which did not change. Reflectance was not affected in tomato. Transmittance generally decreased for leaves at higher positions. Red/far‐red ratios of reflected (R_ratio) and transmitted (T_ratio) light generally decreased in all species, except R_ratio in tomato, where it increased slightly at higher positions. These effects were greater in A. retroflexus compared with C. album and tomato. Changes in these ratios were partly explained by chlorophyll content and leaf mass per area. The results show that leaf position on plant stem influences leaf optical properties in tomato and two weeds and this effect differed between species. These influences and the differences among species could modify red/far‐red ratios in canopies comprising these species, which could influence their growth and inter‐plant interactions.