Impact of red:far red ratios on germination of temperate forest herbs in relation to shade tolerance, seed mass and persistence in the soil.

摘要

The effect of the ratio of red:far red light (R:FR) on seed germination of herbaceous species from northern temperate deciduous forest has received little attention. Here for 27 such species, we investigated the relationship between seed mass and the suitability of micro-sites for germination. Germination in light and in darkness was compared after cold stratification, and for the light-requiring species, the germination response to R:FR was determined. In addition, seed bank persistence was monitored over 4 years. With increasing seed mass, germination became less dependent on light and seed bank persistence decreased. Furthermore, for the light-dependent species, there was a significant negative relationship between the R:FR that resulted in 50% germination and seed mass. These data suggest that small-seeded species only germinate in micro-sites with a high R:FR, which signals the absence of over-topping vegetation or leaf litter. Such micro-sites are comparatively rare, which may necessitate persistence in the soil seed bank. For small-seeded species, we propose that a key benefit from restricting germination to high R:FR is a reduction in the time-frame over which the initially small seedlings remain small and hence highly vulnerable to mortality: high R:FR is likely to indicate high-light levels which would facilitate rapid seedling growth.