Responses of Betula pendula, Picea abies, and Pinus sylvestris seeds to red/far-red ratios as affected by moist chilling and germination temperature

The effect of continuous exposure to various red/far-red ratios (R/FR) on the germination of Betula pendula Roth, Picea abies (L.) Karst., and Pinus sylvestris L. seeds was studied at four different germination temperatures (10, 13, 16, and 20 C) using both moist-chilled and unchilled seeds. Germination of B. pendula seeds was prevented by low R/FR. In B. pendula the relationship between germination probability and R/FR (log(2)) at different temperatures was successfully quantified using parallel logistic curves. The relationship between mean germination time (log(10)) and R/FR (log(2)) was linear. Moist chilling for 3 weeks reduced but did not eliminate the R/FR response in B. pendula. In Picea abies seeds, low R/FR prevented germination at 10 C but not at 13-20 C. Pinus sylvestris seeds did not respond to low R/FR at the studied temperatures. It appears that B. pendula has evolved a light-sensing mechanism that prevents seed germination in shaded conditions. This mechanism could operate more effectively in autumn than in spring after natural moist chilling during overwintering in soil. Picea abies seeds have also evolved a light-sensing mechanism that regulates germination in cool conditions.