Andrea Mondoni

Climate warming could shift the timing of seed germination in alpine plants.

BACKGROUND AND AIMS Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland. METHODS Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site. KEY RESULTS Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species. CONCLUSIONS Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.

Seeds of alpine plants are short lived: implications for long-term conservation

BACKGROUND AND AIMS Alpine plants are considered one of the groups of species most sensitive to the direct and indirect threats to ecosystems caused by land use and climate change. Collecting and banking seeds of plant species is recognized as an effective tool for providing propagating material to re-establish wild plant populations and for habitat repair. However, seeds from cold wet environments have been shown to be relatively short lived in storage, and therefore successful long-term seed conservation for alpine plants may be difficult. Here, the life spans of 69 seed lots representing 63 related species from alpine and lowland locations from northern Italy are compared. METHODS Seeds were placed into experimental storage at 45 °C and 60 % relative humidity (RH) and regularly sampled for germination. The time taken in storage for viability to fall to 50 % (p(50)) was determined using probit analysis and used as a measure of relative seed longevity between seed lots. KEY RESULTS Across species, p(50) at 45 °C and 60 % RH varied from 4·7 to 95·5 d. Seed lots from alpine populations/species had significantly lower p(50) values compared with those from lowland populations/species; the lowland seed lots showed a slower rate of loss of germinability, higher initial seed viability, or both. Seeds were progressively longer lived with increased temperature and decreased rainfall at the collecting site. CONCLUSIONS Seeds of alpine plants are short lived in storage compared with those from lowland populations/related taxa. The lower resistance to ageing in seeds of alpine plants may arise from low selection pressure for seed resistance to ageing and/or damage incurred during seed development due to the cool wet conditions of the alpine climate. Long-term seed conservation of several alpine species using conventional seed banking methods will be problematic.

Habitat-correlated seed germination behaviour in populations of wood anemone ( Anemone nemorosa L.) from northern Italy

Although various aspects of the biology of Anemone nemorosa have been examined, few studies present data on seed germination, and even then information tends to be rather contradictory. A. nemorosa L. is a spring-flowering, woodland geophyte, widely distributed across much of Europe. Germination phenology, including embryo development and radicle and shoot emergence, were investigated in one mountain and three lowland populations from northern Italy. Immediately after harvest, seeds were either sown on agar in the laboratory under simulated seasonal temperatures, or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of dispersal, grew under summer conditions in the laboratory and in the wild. However, seeds did not germinate under continuous summer conditions. Radicle emergence in the field was first recorded at the beginning of autumn, when soil temperatures had dropped to c. 15°C in the case of the three lowland populations, and to c. 10°C at the mountain site. Shoot emergence was delayed under natural conditions until late autumn/early winter, when soil temperatures had dropped to c. 10°C in the lowlands and c. 6°C at the mountain site. In the laboratory, a period of cold stratification was required for shoot emergence, and this requirement was more pronounced in the mountain population. Seeds of the mountain population completed embryo development, radicle emergence and shoot emergence at cooler temperatures compared with the lowland populations. These results suggest that germination in A. nemorosa is highly adapted and finely tuned to local climate. We conclude that seeds of A. nemorosa display deep, simple epicotyl, morphophysiogical dormancy, and this is the first report of such dormancy for the genus Anemone . However, the continuous development and growth of embryos from the time of natural dispersal, and the lack of evidence of developmental arrest under natural conditions, suggests that radicles are non-dormant.

Some like it hot and some like it cold, but not too much: plant responses to climate extremes

Current climatic models predict increasing frequency and magnitude of extreme climatic events (ECEs). Ecological studies recognize the importance of these extremes as drivers of plant growth and mortality, as well as drivers of ecological and evolutionary processes. Here we review observational and experimental studies on ECEs on herbaceous plants and shrubs. Extreme events considered were heat waves, drought, advanced or delayed snowmelt, heavy rainfalls, frosts, pulsed watering and flooding. We analysed 39 studies dealing with direct response of plant to ECEs in different ecosystems, with a particular focus on cold ecosystems (alpine and arctic). Although the number of studies increases every year, the understanding of ecological consequences of ECEs is fragmentary. In general, ECEs affected negatively on physiological processes (efficiency of photosystem II, stomatal conductance and leaf water potential), productivity and reproduction, and had consequences on population demography and recruitment several years after ECE. Indeed, the plant responses to ECEs were species specific and depended on the plant life stage and the timing of ECE. In fact, the magnitude of the effect of ECEs decreased over the growing season. Drought had the most severe effect on plants, while heat waves had minor effect if water was available. The overlap of different ECEs had an additive effect (e.g. drought associated to heat-waves). In general, both neutral or positive plant responses were found and acclimation is possible. In some cases, ECEs exert a strong selective pressure on plant species.

DNA profiling, telomere analysis and antioxidant properties as tools for monitoring ex situ seed longevity.

BACKGROUND AND AIMS The germination test currently represents the most used method to assess seed viability in germplasm banks, despite the difficulties caused by the occurrence of seed dormancy. Furthermore, seed longevity can vary considerably across species and populations from different environments, and studies related to the eco-physiological processes underlying such variations are still limited in their depth. The aim of the present work was the identification of reliable molecular markers that might help in monitoring seed deterioration. METHODS Dry seeds were subjected to artificial ageing and collected at different time points for molecular/biochemical analyses. DNA damage was measured using the RAPD (random amplified polymorphic DNA) approach while the seed antioxidant profile was obtained using both the DPPH (1,1-diphenyl, 2-picrylhydrazyl) assay and the Folin-Ciocalteu reagent method. Electron paramagnetic resonance (EPR) provided profiles of free radicals. Quantitative real-time polymerase chain reaction (QRT-PCR) was used to assess the expression profiles of the antioxidant genes MT2 (type 2 metallothionein) and SOD (superoxide dismutase). A modified QRT-PCR protocol was used to determine telomere length. KEY RESULTS The RAPD profiles highlighted different capacities of the two Silene species to overcome DNA damage induced by artificial ageing. The antioxidant profiles of dry and rehydrated seeds revealed that the high-altitude taxon Silene acaulis was characterized by a lower antioxidant specific activity. Significant upregulation of the MT2 and SOD genes was observed only in the rehydrated seeds of the low-altitude species. Rehydration resulted in telomere lengthening in both Silene species. CONCLUSIONS Different seed viability markers have been selected for plant species showing inherent variation of seed longevity. RAPD analysis, quantification of redox activity of non-enzymatic antioxidant compounds and gene expression profiling provide deeper insights to study seed viability during storage. Telomere lengthening is a promising tool to discriminate between short- and long-lived species.

Environmentally induced transgenerational changes in seed longevity: maternal and genetic influence

BACKGROUND AND AIMS Seed longevity, a fundamental plant trait for ex situ conservation and persistence in the soil of many species, varies across populations and generations that experience different climates. This study investigates the extent to which differences in seed longevity are due to genetic differences and/or modified by adaptive responses to environmental changes. METHODS Seeds of two wild populations of Silene vulgaris from alpine (wA) and lowland (wL) locations and seeds originating from their cultivation in a lowland common garden for two generations (cA1, cL1, cA2 and cL2) were exposed to controlled ageing at 45 °C, 60 % relative humidity and regularly sampled for germination and relative mRNA quantification (SvHSP17.4 and SvNRPD12). KEY RESULTS The parental plant growth environment affected the longevity of seeds with high plasticity. Seeds of wL were significantly longer lived than those of wA. However, when alpine plants were grown in the common garden, longevity doubled for the first generation of seeds produced (cA1). Conversely, longevity was similar in all lowland seed lots and did not increase in the second generation of seeds produced from alpine plants grown in the common garden (cA2). Analysis of parental effects on mRNA seed provisioning indicated that the accumulation of gene transcripts involved in tolerance to heat stress was highest in wL, cL1 and cL2, followed by cA1, cA2 and wA. CONCLUSIONS Seed longevity has a genetic basis, but may show strong adaptive responses, which are associated with differential accumulation of mRNA via parental effects. Adaptive adjustments of seed longevity due to transgenerational plasticity may play a fundamental role in the survival and persistence of the species in the face of future environmental challenges. The results suggest that regeneration location may have important implications for the conservation of alpine plants held in seed banks.

Effects of Autumn and Spring Heat Waves on Seed Germination of High Mountain Plants

Alpine plants are considered to be particularly vulnerable to climate change and related extreme episodes, such as heat waves. Despite growing interest in the impact of heat waves on alpine plants, knowledge about their effects on regeneration is still fragmentary. Recruitment from seeds will be crucial for the successful migration and survival of these species and will play a key role in their future adaptation to climate change. In this study, we assessed the impacts of heat waves on the seed germination of 53 high mountain plants from the Northern Apennines (Italy). The seeds were exposed to laboratory simulations of three seasonal temperature treatments, derived from real data recorded at a meteorological station near the species growing site, which included two heat wave episodes that occurred both in spring 2003 and in autumn 2011. Moreover, to consider the effect of increasing drought conditions related to heat waves, seed germination was also investigated under four different water potentials. In the absence of heat waves, seed germination mainly occurred in spring, after seeds had experienced autumn and winter seasons. However, heat waves resulted in a significant increase of spring germination in c. 30% of the species and elicited autumn germination in 50%. When heat waves were coupled with drought, seed germination decreased in all species, but did not stop completely. Our results suggest that in the future, heat waves will affect the germination phenology of alpine plants, especially conditionally dormant and strictly cold-adapted chorotypes, by shifting the emergence time from spring to autumn and by increasing the proportion of emerged seedlings. The detrimental effects of heat waves on recruitment success is less likely to be due to the inhibition of seed germination per se, but rather due to seedling survival in seasons, and temperature and water conditions that they are not used to experiencing. Changes in the proportion and timing of emergence suggest that there may be major implications for future plant population size and structure.

Temperature controls seed germination and dormancy in the European woodland herbaceous perennial Erythronium dens-canis (Liliaceae)

We examined the germination ecology and the temperature requirements for germination of Erythronium dens-canis, under both outdoor and laboratory conditions. E. dens-canis is a spring flowering woodland geophyte widely distributed across Europe. Germination phenology, including embryo development and radicle and cotyledon emergence, were investigated in a natural population growing in Northern Italy. Immediately after harvest, seeds of E. dens-canis were either sown on agar in the laboratory under simulated seasonal temperatures or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of seed dispersal, grew during summer and autumn conditions in the laboratory and in the wild, culminating in radicle emergence in winter when temperatures fell to ≈ 5 °C. Emergence of cotyledons did not occur immediately after radicle emergence, but was delayed until the end of winter. Laboratory experiments showed that temperature is the main factor controlling dormancy and germination, with seeds becoming non-dormant only when given warmth, followed by cold stratification. Unlike seeds of E. dens-canis that germinate in winter, in other Erythronium species radicle emergence occurs in autumn, while in some it is delayed until seeds are transferred from winter to spring conditions. Our results suggest that there is genetic and environmental control of the expression of seed dormancy amongst Erythronium species, which is related to local climate.

Habitat-related germination behaviour and emergence phenology in the woodland geophyte Anemone ranunculoides L. (Ranunculaceae) from northern Italy

This study examined whether the restricted habitat preference of the spring-flowering woodland geophyte Anemone ranunculoides L., compared with that of A. nemorosa growing in the same woodlands in northern Italy, could be explained by subtle differences in germination preference and emergence phenology. Immediately after harvest, seeds of A. ranunculoides were either sown on agar in the laboratory under simulated seasonal temperatures or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of seed dispersal, grew during summer in the laboratory and in the wild, culminating in radicle emergence in the autumn, when temperatures fell to c. 15°C. Shoot emergence was delayed under natural conditions until soil temperature had dropped further to c. 10°C. Compared with populations of the closely related Anemone nemorosa L. occupying the same woodland habitat, which have been reported to have non-dormant radicles, A. ranunculoides displayed a narrower temperature tolerance for radicle emergence and high levels of germination were possible only after prolonged exposure to summer conditions, indicating physiological dormancy. However, unlike A. nemorosa , shoot emergence in A. ranunculoides was not dependent on winter temperatures, suggesting weaker epicotyl morphophysiological dormancy. Under a regime of diurnal temperature alternation, simulating the microclimate where there is little plant cover, germination failed almost completely; this could explain the absence of A. ranunculoides in open habitats.

Habitat-related seed germination traits in alpine habitats

Abstract Understanding the key aspects of plant regeneration from seeds is crucial in assessing species assembly to their habitats. However, the regenerative traits of seed dormancy and germination are underrepresented in this context. In the alpine zone, the large species and microhabitat diversity provide an ideal context to assess habitat‐related regenerative strategies. To this end, seeds of 53 species growing in alpine siliceous and calcareous habitats (6230 and 6170 of EU Directive 92/43, respectively) were exposed to different temperature treatments under controlled laboratory conditions. Germination strategies in each habitat were identified by clustering with k‐means. Then, phylogenetic least squares correlations (PGLS) were fitted to assess germination and dormancy differences between species’ main habitat (calcareous and siliceous), microhabitat (grasslands, heaths, rocky, and species with no specific microhabitats), and chorology (arctic–alpine and continental). Calcareous and siliceous grasslands significantly differ in their germination behaviour with a slow, mostly overwinter germination and high germination under all conditions, respectively. Species with high overwinter germination occurs mostly in heaths and have an arctic–alpine distribution. Meanwhile, species with low or high germinability in general inhabit in grasslands or have no specific microhabitat (they belong to generalist), respectively. Alpine species use different germination strategies depending on habitat provenance, species’ main microhabitat, and chorotype. Such differences may reflect adaptations to local environmental conditions and highlight the functional role of germination and dormancy in community ecology.