Phenotypic plasticity in seed dormancy may allow plant species to cope with rapid environmental changes, such as climate warming. In controlled experimental settings, plasticity in dormancy has been found to relate to temperature during seed maturation, but this relationship has not been tested in field conditions. Here we analyse for the first time the variation in dormancy during five successive years in wild populations of the study species Centaurium somedanum, to determine how this variation is related to average temperatures during specific seasons of plant activity. We performed laboratory germination experiments to measure: (1) the degree of dormancy at dispersal; and (2) the sensitivity to dormancy-breaking factors. We calculated average temperatures during four seasons of plant activity (overwintering, vegetative growth, flowering and seed maturation) for each year, and tested the relationship between these temperatures and patterns of dormancy variation, using Generalized Linear Models. Dormancy varied among sites and years, seeds being more dormant in colder years. For the degree of dormancy at dispersal, we found a positive relationship with flowering temperature and a significant effect of collection site. For the sensitivity to dormancy-breaking factors, we found no significant differences among sites, a positive relationship with flowering temperature and a negative relationship with overwintering temperature. Phenotypic plasticity in dormancy in C. somedanum is thus especially marked in the sensitivity to dormancy-breaking factors. Temperatures during overwintering and flowering have differential effects on this plasticity, allowing the plant to detect the gradient of seasonality, a main ecological feature of its distribution. These results highlight the importance of taking into account more than average temperatures when assessing the response of plant phenotypic plasticity to climate change.

Seeds with epicotyl dormancy reside in soil up to 15 months (or longer), being exposed to a sequence of temperatures, before seedlings completely emerge (i.e. with both roots and shoots). Heretofore, few studies have examined precise temperatures, especially in sequences, for promotion of radicle and cotyledon emergence and how they relate to environmental cues in nature. Viburnum is the best known genus to exhibit epicotyl dormancy and, as such, we investigated the Japanese V.furcatum, hypothesizing a similar kind and level of dormancy. The underdeveloped embryos in mature seeds in October were spatulate shaped, unlike those in other Viburnum species, and they elongated from late June to August of the following year. Radicles emerged after embryo growth until mid-October, followed by cotyledons from mid-April to mid-May. Temperatures required for embryo growth, radicle and cotyledon emergence in the laboratory approximated closely those in the field. Embryo elongation and radicle emergence occurred at warm temperature regimes, and gibberellic acid (GA3) did not substitute for this warm temperature requirements. Following a 120-d cold stratification of seeds with an emerged radicle, shoots emerged from seeds at 10, 15, 15/5, 20/10 and 25/15°C. We identified that seeds of V. furcatum have deep simple epicotyl morphophysiological dormancy like the majority of other Viburnum species. For propagation of the species from seeds, the nearly 2-year period for seedling emergence could be shortened to 8 months: start fresh seeds at 25/15°C (60 d) and then move them through a sequence of 15/5°C (30 d) →  0°C (120 d) →  20/10°C (30 d).

Several studies have compared seed banks of the different morphs of heteromorphic species, but none of them was on an amphi-basicarpic species. Our primary aim was to compare the relative ability of aerial and basal diaspores of an amphi-basicarpic species to form a seed bank. We compared the seed-bank dynamics of basal and aerial diaspores of three populations of the cold-desert annual Ceratocarpus arenarius growing in the Junggar Desert in north-western China. A 2.5-year experimental garden study compared germination phenology and retention of viability in basal (a) and aerial (c and f) morphs. Aerial morphs formed a modified Thompson and Grime type III seed bank (small proportion of seeds carried over to next year) and the basal morph a modified type IV seed bank (large proportion of seeds carried over to next year). Seeds germinated only in spring, and cumulative germination percentages were f>c>a (year 1), f = c>a (year 2) and f = c = a (year 3). The relationship between length of germination period, retention of viability during burial and relative ability to form a persistent seed bank was basal morph > aerial morphs. The results of this seed-bank study on C. arenarius are in full agreement with those published previously on seed dispersal and dormancy in this species. Thus, strong additional support is provided for a high risk–low risk germination strategy in this cold-desert annual.

Although Asteraceae species are important in the cold deserts of Central Asia, little is known about their seed dormancy and germination. We determined dormancy breaking and germination requirements of three annual Asteraceae, Echinops gmelinii, Epilasia acrolasia and Koelpinia linearis. Achenes (seeds) were tested for germination in light and in darkness over a range of alternating temperatures after various periods of burial outdoors and of dry storage. Germination phenology was monitored for seeds sown in irrigated and non-irrigated sand, and temperature requirements for dormancy break were determined under wet and dry conditions. Effects of pericarp and phyllaries on germination of E. acrolasia and E. gmelinii, respectively, were determined. Low percentages of 20-day-old seeds of E. acrolasia and K. linearis were non-dormant and germinated to low percentages over the range of temperatures, whereas all seeds of E. gmelinii were dormant. As seeds of the three species afterripened, they germinated over the range of temperatures. Whether seeds germinated in autumn or spring depended on the amount of sand moisture. Mechanical resistance of the pericarp and phyllaries reduced germination of E. acrolasia and E. gmelinii, respectively. Temperature requirements for germination as seeds come out of dormancy do not correspond to any of the known five types of non-deep physiological dormancy (PD). Thus, a sixth type is recognized in which germination occurs over the same range of temperatures in the early and late stages of dormancy break. Type 6 allows seeds to germinate at high or at low temperatures, whenever sand moisture is non-limiting.

The soil seed bank is the reserve of viable seeds found in the soil. This reserve contributes to plant population persistence in unpredictable environments; thus, determining its presence is basic to understanding recruitment patterns and population dynamics. Studies of soil seed banks in the Cactaceae are scarce, although these plants are ecologically dominant in American arid and semi-arid environments. Most studies have inferred the presence of seed banks by analysing morphological seed traits or germination of seeds stored in the laboratory for different periods of time. Few studies have determined their presence through evaluation of distribution, density and longevity of seeds in the field. To fill this information gap, we determined the existence of, and studied, the soil seed bank of Stenocereus stellatus, a columnar cactus endemic to central Mexico. This study reports the evaluation of these characteristics in the field and discusses whether this species forms a soil seed bank. We found a higher number of seeds under shrubs than in areas lacking vegetation. Recently dispersed seeds did not germinate because they have primary dormancy. This dormancy was broken after 6 months of burial in the soil. Seeds buried for 10 months entered secondary dormancy and they were not viable at 24 months, probably because of pathogen attack. Considering dormancy and seed longevity, we suggest that S. stellatus has the potential to form a short-term persistent seed bank. However, this should be confirmed by conducting studies on other S. stellatus populations throughout their geographical distribution.

A population-based modelling approach was used to predict the occurrence of germination in Solanum sarrachoides (SOLSA) for different treatments. Seeds collected in Toledo (Spain) were exposed to constant temperatures, to temperatures alternating between 10 and 30°C and to gibberellins (GAs; 0, 50, 100, 150 and 1000 ppm) during a 24-h imbibition period. The following parameters were measured: base temperature (Tb), mean thermal time (θT (50)) and the standard deviation of thermal time (σθT ). The SOLSA seeds only germinated at constant temperatures when the highest GA concentration was applied. The thermal model suggests that the induction and loss of physiological dormancy following seed dispersal is achieved when temperatures vary and when a mean thermal time of 66 growing degree-days (d°C) and a Tb value of 16°C are achieved when no GA treatment was added. The concentration of GA applied under conditions of alternating temperatures has an additive effect, reducing θT (50) up to threefold, from basal level (66 d°C) to 19.40 d°C, when the 1000 ppm GA treatment was applied. In this last case, the germination was accelerated by reducing Tb to 14°C. A 5–10°C change in temperature and a range of average temperatures of 20–27.5°C promoted the germination of SOLSA seeds to the greatest extent in the absence of GA. However, these conditions are not frequently encountered in the irrigated areas of the studied region; this finding could explain the limited ability of SOLSA to expand its range within this area.

Rouya polygama (Apiaceae) is an endangered Mediterranean species of great phytogeographical and ecological interest, growing on coastal sandy dunes. Intraspecific variability in the responses to constant temperatures (5–25°C) and an alternating temperature regime (25/10°C), salt stress (0–600 mM NaCl) and recovery of seed germination was evaluated among six populations from Sardinia and Corsica. Seeds were non-dormant and germination percentages ranged from 10 to 83%, depending on temperature and population. Differences in germination percentages were mainly due to different seed mortality among seed lots. R. polygama seeds germinated in salt concentrations up to 200 mM NaCl, whereas higher salt concentrations totally inhibited germination. Salt affected seed viability, and the recovery response decreased with increasing salinity and temperature. Inter-population variability and different sensitivity to NaCl in seed germination were detected. Our results are consistent with field germination in a period from autumn to spring, when water is available in the soil and temperatures are not prohibitive for seedling establishment, representing an advantageous ecological adaptation for seedling establishment to the unpredictable Mediterranean rainfall pattern. Further studies on R. polygama are needed to investigate germination requirements at temperatures higher than 25°C and its germination in the field, and to clarify genetic inter-population variability, considering a higher number of populations and possibly extending to North African populations.

Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is an important technology to analyse gene expression levels during plant development or in response to different treatments. An important requirement to measure gene expression levels accurately is a properly validated set of reference genes. In this context, we analysed the potential use of 17 candidate reference genes across a diverse set of samples, including several tissues, different stages and environmental conditions, encompassing seed germination and seedling growth in Ricinus communis L. These genes were tested by RT-qPCR and ranked according to the stability of their expression using two different approaches: GeNorm and NormFinder. GeNorm and Normfinder indicated that ACT, POB and PP2AA1 comprise the optimal combination for normalization of gene expression data in inter-tissue (heterogeneous sample panel) studies. We also describe the optimal combination of reference genes for a subset of root, endosperm and cotyledon samples. In general, the most stable genes suggested by GeNorm are very consistent with those indicated by NormFinder, which highlights the strength of the selection of reference genes in our study. We also validated the selected reference genes by normalizing the expression levels of three target genes involved in energy metabolism with the reference genes suggested by GeNorm and NormFinder. The approach used in this study to identify stably expressed genes, and thus potential reference genes, was applied successfully for R. communis and it provides important guidelines for RT-qPCR studies in seeds and seedlings for other species (especially in those cases where extensive microarray data are not available).

The understanding that many aspects of the spatial and temporal patterns of epiphyte communities may be explained by the comportment of early life stages has given rise to a considerable number of germination studies in recent years. Unfortunately, protocols frequently use unproven assumptions and arbitrary experimental conditions. To make future studies as ecologically meaningful as possible we address a number of potential pitfalls with a series of experiments with seeds from a total of 16 species. We show that it is safe to collect capsules for experiments before natural dehiscence – there is afterripening even in the case of very early collections. The application of fluctuating temperatures is not imperative, because there is no consistent difference in the germination response under constant versus fluctuating temperatures. The effects of different osmotic potentials and intermittent drought of varying intensity on germination are qualitatively, but not quantitatively, comparable. Due to the greater ecological realism, we encourage the use of the latter. However, care must be taken to use realistic temperatures – the impact of intermittent drought on germination is modulated by temperature. This highlights the need for data on the in situ temperature regimes during germination as an important prerequisite towards more realistic experiments in the field of germination ecology of vascular epiphytes.