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

Abstract

Summary1. 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. 2. 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. 3. 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. 4. 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.

Weed Seedbank in Rice Fields

“…This is the case for the weed species that produce seeds that are photoblastic positive, that is, need light to germinate, such as Amaranthus retroflexus [53], Eclipta alba [54], Hyptis suaveolens [55], Digitaria spp. [56], Urtica dioica [57], Ageratum conyzoides [23,58], Fimbristylis autumnalis [23] and Cyperus aggregatus [59].…”

Towards an Understanding of Factors Controlling Seed Bank Composition and Longevity in the Alpine Environment

“…Since light can only penetrate a few millimeters from the top of the soil surface, seeds found below this depth do not germinate; and even in dark-requiring species, those seedlings would die before reaching the soil surface, especially if they are small owing to the smaller seedling size (see below). Data on other ecosystems suggest that seeds that are smaller are more likely to require light for germination than larger seeds (Milberg et al, 2000;Jankowska-Blaszczuk and Daws, 2007). In a recent study, Wu et al (2013 ) found a similar pattern in alpine species of Qinghai-Tibetan Plateau.…”

Variation in dormancy and germination in three co-occurring perennial forest herbs

“…We found elaiosome effects to be highly variable and detected statistically significant differences between S. canadensis seed populations (±elaiosome) in only one instance, perhaps because we considered seedling emergence across the entire annual temperature cycle and accounted for mortality and dormancy in seed populations (also see Christian and Stanton 2004;Martins et al 2009). Although light was not evaluated in this study, photoblastic germination is unlikely since seedlings emerged in packets buried belowground, and the seed mass for each species exceeded the threshold (1.5 mg) for light-dependent germination observed in other temperate forest herbs (Jankowska-Blaszczuk and Daws 2007).…”