A thermal time basis for comparing the germination requirements of some British herbaceous plants

Abstract

The effect of temperature on germination rate was assessed for seeds of 31 wild plant species and four cultivated species growing in the UK. The temperature at which seed first germinated ranged from 2mC (Brassica rapa) to 11mC (several species). As the temperature progressively increased, the percentage of seed that germinated rapidly increased to near 100%, whereas the duration for germination progressively decreased up to the thermal optimum. Above the thermal optimum, the duration for germination initially remained constant, and then rapidly increased until the thermal maximum was exceeded when no seed germinated. To assess the effect of temperature on germination rates, the reciprocal of the duration (1\duration) for 50% germination was calculated and regressed against temperature. For most species a linear regression accounted for 90% of the variation in germination rates for temperatures up to the thermal optimum. From the regressions, the base temperatures (T b , below which no germination is expected) and the thermal constant (S, expressed in degree days) for 50% germination were calculated. The extremes were the alpine species Dryas octopetala, which had a high T b (c. 12.0mC) and low S (26 degree days), and Saxifraga tridactylites which had a low estimated T b (c. k1.8mC) and a high S (136 degree days). The estimated value of S increased with increasing percentage germination, and although S varied considerably between species with similar values of T b , a weak inverse relationship between T b and S was indicated. A thermal time approach was shown to be useful when analysing and comparing thermal requirements for germination of the seed of wild plant species. It showed, for example, that percentage germination often decreased as temperatures approached T b , and that for some seed germination ceased at temperatures well above T b .

A Modified Thermal Time Model Quantifying Germination Response to Temperature for C3 and C4 Species in Temperate Grassland

“…Among the 27 species in this study, the differences in base temperature were not significant between annuals and perennials, but the differences in thermal time constant were significant between annuals and perennials (16.0 °C·d and 26.2 °C·d, respectively; p < 0.01). This result was consistent with previous research [17], which indicated that germination responses to temperature was related to plant life cycle. Compared to tropical and subtropical legumes [18], the temperate grassland species in our study had lower base temperature and thermal time constants.…”

“…However, most studies use the thermal time model to investigate intraspecific variation of germination or differences between several species [3,[14][15][16]. However, comparison of thermal time model parameters between large numbers of species and between different functional groups is lacking [17,18]. Knowing and comparing the base temperature and thermal time constant at the species level can increase our ability to predict species distribution shift under climate change.…”

Correspondence of seed traits with niche position in glacier foreland succession

“…Most commonly, T opt is defined as the temperature at which germination is most rapid and it was reported that FGP correlates linearly with GR 50% at temperatures lower than T opt , whereas the both measures are usually decoupled at higher temperatures (Trudgill et al 2000). Thus, these two measures of germination may have different ecological relevance, but the underlying relations are not yet examined adequately.…”

“…Olff et al (1994) illustrated that germination characteristics can be used to explain species occurrence in a lowland secondary succession. The optimum temperature of germination (T opt ) is commonly speciesspecific (Trudgill et al 2000) and affects the regeneration in terms of emergence timing and abundance of seedlings (Probert 2000). Although the germination responses of various alpine species have been widely investigated with respect to temperature (Billings and Mooney 1968;Cavieres and Arroyo 2000;Giménez-Benavides et al 2005;Shimono and Kudo 2005;Wagner and Simons 2009), knowledge on temperature ranges and T opt of alpine species is still scarce.…”

Thermal time requirements for germination, emergence and seedling development of adventive legume and grass species

“…This is now frequently used to integrate more complex biological processes inpoikilothermic species, supporting some practical and ecological implications (Trudgill et al 2005). Thermal time has been used to analyse the effect of temperature on germination or both germination and emergence in non-limiting moisture conditions of several commercial herbaceous species (Moot et al 2000;Trudgill et al 2000;Larsen & Bibby 2005;Black et al 2006). A mathematical model to describe germination percentage dependency on time and temperature in Amaranthus patulus under sub-optimal temperature conditions has also been developed (Washitani & Takenaka 1984).…”