Frost Sensitivity Research Articles

Full-length transcriptome reveals the pivotal role of ABA and ethylene in the cold stress response of Tetrastigma hemsleyanum.

Tetrastigma hemsleyanum is a valuable herb widely used in Chinese traditional and modern medicine. Winter cold severely limits the artificial cultivation of this plant, but the physiological and molecular mechanisms upon exposure to cold stress in T. hemsleyanum are unclear. T. hemsleyanum plants with different geographical origins exhibit large differences in response to cold stress. In this research study, using T. hemsleyanum ecotypes that exhibit frost tolerance (FR) and frost sensitivity (FS), we analyzed the response of cottage seedlings to a simulated frost treatment; plant hormones were induced with both short (2 h) and long (9 h) frost treatments, which were used to construct the full-length transcriptome and obtained 76,750 transcripts with all transcripts mapped to 28,805 genes, and 27,215 genes, respectively, annotated to databases. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed enrichment in plant hormone signaling pathways. Further analysis shows that differently expressed genes (DEGs) concentrated on calcium signaling, ABA biosynthesis and signal transduction, and ethylene in response to cold stress. We also found that endogenous ABA and ethylene content were increased after cold treatment, and exogenous ABA and ethylene significantly improved cold tolerance in both ecotypes. Our results elucidated the pivotal role of ABA and ethylene in response to cold stress in T. hemsleyanum and identified key genes.

Spring emergence and canopy development strategies in miscanthus hybrids in Mediterranean, continental and maritime European climates

AbstractDue to its versatility and storability, biomass is an important resource for renewable materials and energy. Miscanthus hybrids combine high yield potential, low input demand, tolerance of certain marginal land types and several ecosystem benefits. To date, miscanthus breeding has focussed on increasing yield potential by maximising radiation interception through: (1) selection for early emergence, (2) increasing the growth rate to reach canopy closure as fast as possible, and (3) delayed flowering and senescence. The objective of this study is to compare early season re‐growth in miscanthus hybrids cultivated across Europe. Determination of differences in early canopy development on end‐of‐year yield traits is required to provide information for breeding decisions to improve future crop performance. For this purpose, a trial was planted with four miscanthus hybrids (two novel seed‐based hybrids M. sinensis × sinensis [M sin × sin] and M. sacchariflorus × sinensis [M sac × sin], a novel rhizome‐based M sac × sin and a standard Miscanthus × giganteus [M × g] clone) in the UK, Germany, Croatia and Italy, and was monitored in the third and fourth growing season. We determined differences between the hybrids in base temperature, frost sensitivity and emergence strategy. M × g and M sac × sin mainly emerged from belowground plant organs, producing fewer but thicker shoots at the beginning of the growing season but these shoots were susceptible to air frosts (determined by recording 0°C 2 m above ground surface). By contrast, M sin × sin emerged 10 days earlier, avoiding damage by late spring frosts and producing a high number of thinner shoots from aboveground shoots. Therefore, we recommend cultivating M sac × sin at locations with low risk and M sin × sin at locations with higher risk of late spring frosts. Selecting miscanthus hybrids that produce shoots throughout the vegetation period is an effective strategy to limit the risk of late frost damage and avoid reduction in yield from a shortened growing season.

Temporal and Spatial Positioning of Service Crops in Cereals Affects Yield and Weed Control

Leguminous service crops (SCs) can provide multiple services to cropping systems, reducing the reliance on external resources if sufficient biomass is produced. However, rapid light and temperature reductions limit post-harvest cultivation of SCs in Northern Europe. A novel practice of intercropping SCs in two consecutive crops (spring–winter cereal) to extend the period of SCs growth, and hence improve yield and reduce weeds, was tested. Three spatial and temporal arrangements of SCs and cash crops were investigated, as well as three SC mixtures, characterized by their longevity and frost sensitivity. Compared to no SC, the best performing mixture, frost-tolerant annuals, increased grain and N yield of winter wheat by 10% and 19%, respectively, and reduced weed biomass by 15% and 26% in oats and winter wheat, respectively. These effects were attributed to high biomass production and winter survival. However, this SC reduced oat yields by 15% compared to no SC. Furthermore, SC growth and service provision varied largely between experiments, driven by the weather conditions. Extending the SC’s growth period by intercropping in two consecutive cereal crops has potential, but locally adapted species choices and establishment strategies are needed to ensure SC vitality until termination.

Contrast in vulnerability to freezing-induced xylem embolism contributes to divergence in spring phenology between diffuse- and ring-porous temperate trees

The spring phenology and growth strategy of temperate tree species can be strongly linked to their sensitivity to frosts, which deserve more profound investigations under the background of climate warming particularly considering the advancement of spring phenology as well as the increase in frequency and intensity of spring cold waves. Spring phenologies, stem radial growth characteristics, frost sensitivity of leaves and stem hydraulic systems were studied in five diffuse-porous and five ring-porous temperate tree species under a common garden condition. The results showed that the spring leaf phenology of the diffuse-porous species was one to two weeks earlier than that of the ring-porous species. The ring-porous species had significantly higher stem hydraulic conductivity than the diffuse-porous species (1.81 and 0.95 kg·m −1 ·s −1 ·MPa −1 , P < 0.05) but were more vulnerable to freeze-thaw induced xylem embolism than the latter. After a simulated freeze-thaw event, the average percentage loss of hydraulic conductivity in the current year shoots increased from 26.0% (native embolism) to 86.7% in the ring-porous species, while it only increased from 21.3% to 38.3% in the diffuse-porous species. The spring phenology was clearly correlated with vulnerability to freeze-thaw induced embolism, with the more vulnerable ring-porous species exhibited substantially delayed phenology to reduce risks of catastrophic hydraulic dysfunction during spring frosts. Nevertheless, ring-porous species can offset the postponed onset of growth and gained even higher annual growth due to significantly higher hydraulic efficiency and leaf gas exchange rates. Contrasts between ring-porous and diffuse-porous species in resistance to freeze-thaw induced embolism suggest that they face different selective pressures from early spring frosts, which may at least be partially responsible for their divergence in spring phenology and growth strategy and can potentially lead to different responses to climate regime shifts.

A 15-year long assessment of cold hardiness of apricot flower buds and flowers during the blooming period

Long-term examinations are important for accurately dissecting the genotypic and environmental factors of and for predicting the possible impacts of climate change on quantitative traits, such as the frost tolerance of apricot generative organs during the floral developmental period. In our experimental work the cold hardiness of flower buds and flowers of three apricot cultivars [‘Ceglédi bíborkajszi’ (CBK), ‘Gönci magyar kajszi’ (GMK) and ‘Rózsakajszi C.1406’ (RK)] was studied systematically in different phenological stages, applying a standardised artificial freezing test protocol on samples collected from the orchard during a period of 15 consecutive years. Based on the results, both the genotypes and the years were highly significant components of frost tolerance; at the early phases the greater effect of years, while at the later stages that of the genotypes were detected. RK was frost tolerant and more stable across the years, while CBK was the most frost sensitive, which was accompanied by a significantly higher sensitivity to seasonal differences. Positive correlation was found between the starting time of blooming and frost tolerance of flowers, the significance of which intensified with the frost sensitivity of the apricot genotype. Significant associations were identified between various meteorological parameters of the 8-month period prevailing flowering and frost tolerance of apricot flowers during blooming. Possible effects of climate change on the local weather conditions were also detected with significant impacts on the phenological processes of floral buds, on the timing of flowering and on frost tolerance.

Modelling the impact of climate change on the occurrence of frost damage in Sitka spruce (Picea sitchensis) in Great Britain

Abstract Climate change is predicted to increase temperature and seasonal temperature variance in Great Britain (GB). Sitka spruce (Picea sitchensis (Bong.) Carr) is the most important tree species used in commercial plantations throughout Europe and GB. Frosts that occur outside the winter dormancy period can negatively affect trees, since they happen after dehardening. Damage can be especially severe at bud burst, before emerging needles mature and form protective barriers. Here, we modelled the impact of climate change on frost sensitivity in Sitka spruce with temperature data from five climate projections. The UKCP09 climate model HadRm3 uses emission scenario SRESA1B for the years 2020–2099. The global and downscaled versions of the UKCP18 HadGem3 model use the emissions scenario RCP 8.5. The global model CMCC-CM uses the RCP 4.5 and RCP 8.5 emissions scenarios. The predictions based on these models were compared with results from gridded historical data for the period 1960–2015. Three indicators that assessed the frost sensitivity of Sitka spruce were explored: the total number of frosts between the onset of dehardening and the end of summer, which use three different temperature thresholds (Index 10°C, 1–3°C, 1–5°C); the total number of frosts after bud burst (Index 2); the number of days with minimum temperatures below the resistance level (backlashes) during the hardening–dehardening period (September–August) (Index 3). The indices were validated with historical data for frost damage across GB, and Index 1–3°C, Index 1–5°C and Index 3 were shown to be significantly correlated. The frequency of all frosts and backlashes is expected to decrease with climate change, especially under higher emissions scenarios. Post-bud burst frosts have been historically very rare in GB and remain so with climate change. Downscaled regional climate models detect geographic variability within GB and improve prediction of overall trends in frost damage in comparison to global climate change models for GB.

English

Mango cultivation is one of the key economic agricultural activities of fruit in Brazil. In Southern Brazil, mango presents vulnerability thanks to its frost sensitivity, indicating the relevance of climate studies to improve the production and agricultural techniques, in the context of sustainable agriculture and climate change. Agroclimatic zoning should be one of the first information to be considered when starting its cultivation. The objective of this study is to carry out climatic risk zoning for mango tree (Mangifera indica) in the basin of Paran&aacute; River III, Brazil. Meteorological data from 43 stations, from 1976 to 2018, were used. The climatic risk analysis was based on the requirements of the mango for precipitation, water balance, average annual temperature, and frost tolerance. The occurrence of frosts is the key restrict factor for production in the area of study. This meteorological factor restricted mango cultivation in the central-eastern portion of the basin. In other areas, the risk is present but the mango cultivation is recommended. Key words: Climate aptitude, climate variability, agricultural planning. &nbsp;

Feeding pollinators from weeds could promote pollen allergy. A simulation study

Abstract Weed pollen both feeds many insects and causes allergies in humans. The objective of the study was to investigate the determinants in terms of management practices and weed species traits on those pollen-borne services and dissservices (hence (dis)services). We developed a set of indicators to assess the magnitude of these (dis)services combining species pollinating values (or allergizing potential) with species densities by means of the CONTRA method for designing fuzzy decision trees. Densities were calculated by the process-based weed dynamics model F lor S ys , which simulates the dynamics of a multispecies weed flora at a daily time step and over the years depending on the field's cropping system and pedoclimate. We then simulated a virtual farm-field network consisting of 272 cropping systems from 7 regions in France and Spain, with F lor S ys over 27 years and with 10 weather repetitions. The simulated weed flora and (dis)service indicators were analysed with analyses of variance, regression trees, RLQ and fourth-corner analyses. The simulations showed that the management practices that increased pollen-borne allergy risk were also often those providing large trophic resources for butterflies and, to a lesser degree, to other pollinating insects. Practices reducing pollen-borne (dis)services included frequent and intensive tillage, frequent spring crops, herbicides sprayed on cash crops, preferably broad-spectrum products targeting emerged weeds but the effect of all these techniques greatly varied with the date of their implementation. The weed species that most contributed to pollinator food were those that were present and growing best during the critical feeding period of the pollinators rather than those with the largest pollinating value or those with the largest densities during the cropping campaign. Species characteristics favouring pollinator food included low dormancy, tall “stemmy” plants and high temperature requirements in terms of photosynthesis and frost sensitivity. Then, we identified the management strategies that reconciled pollinator food with low allergy risk. For instance, direct sowing or several weeks without tillage after harvest or prior to crop sowing increase food offer. Finally, we proposed rules for ex post monitoring following the introduction of novel crops or management techniques. For instance, ex post biodiversity monitoring following the introduction of glyphosate-tolerant maize should focus on situations with frequent tillage and on the presence of butterflies.

Avocado diseases affecting fruit quality

Abstract The avocado ( Persea americana Mill.) is from an ancient plant lineage, the Lauraceae. Although evidence for human consumption dates back 15,000 years, commercialisation has occurred only over the last 150 years. The most commonly traded variety was first the green-skin ‘Fuerte’ (green as it ripens), and more recently ‘Hass’, on which skin darkens when ripe. Production has been increasing worldwide, and currently about 64 countries produce avocados. The range of climates is from arid to very high rainfall and from tropical to temperate. The minimum daily temperatures are above 5°C in all avocado-growing regions because of frost sensitivity. Apart from avocado sunblotch viroid (ASBVd), most avocado fruit diseases are caused by fungi. Some fungi cause visible symptoms resulting in unmarketable fruit, and other infections in the orchard are symptomless. These symptomless infections express as rots after harvest during cold storage, transport and ripening. Most post-harvest pathogens infect through both the body of the fruit and the stem-end wound, while a few infect only through the stem-end wound. The geographic distribution of these fungi varies possibly because of differences in environmental requirements and effective quarantine measures during trade. Fungal rots can be reduced by the application of fungicides in the orchard, removing inoculum residing in dead branches and mummified fruit in the canopy, ensuring high-calcium levels in the fruit flesh are maintained, careful post-harvest handling and selling fruit as soon after harvest as possible. Some post-harvest fungicides can be effective.

Occurrence of ‘blue’ and ‘frost’ rings reveal frost sensitivity of eastern Baltic provenances of Scots pine

Assisted gene flow is advised as one of the most effective means to sustain the productivity of forests under warming climate via application of the provenances (genotypes) capable to utilize longer vegetation season. Nevertheless in the temperate and boreal zones, the extension of vegetation period also subjects trees to effects of frosts, which can have severe economic impact under warming climate. In this study, wood anatomical anomalies related to late frosts in spring (‘frost’ rings) and early frosts in late summer (‘blue’ rings) for the eastern Baltic provenances of Scots pine (Pinus sylvestris L.) with a contrasting field performance were analysed retrospectively. Three trials with the age of 40 year in Latvia were sampled. The frost-related wood anomalies were identified using microscopy methods. Generalized mixed effects models were used to assess the effect of provenance on the probability of frost damage, accounting for the design of the trials, as well as for the inter-annual variability. The overall mean probability of frost-related wood anomalies was low (ca. 0.025), yet it increased with continentality of the trials, showing limited relation to the inter-annual variability of minimum temperatures. The probability of anomalies decreased with age. Provenance had a significant effect on the occurrence of ‘frost’ and ‘blue’ rings, implying genetically determined frost sensitivity, while the genotype (provenance) by environment (trial) interaction indicated high phenotypic plasticity of the trees. The probability of anomalies appeared related to the field performance of the provenances. The low-performing provenances (Dippoldiswalde and Eibenstock, which originated from the Orr Mountains) were most sensitive to frost, while the top-performing ones (Rytel and, particularly, Güstrow, which originated from coastal areas) showed only a few anomalies, indicating the linkage between frost sensitivity and growth. The local provenance, which showed an average field performance, also showed intermediate sensitivity to early frosts, thus supporting a necessity for the assisted gene flow in the eastern Baltic region.

Distribution of pines in the Iberian Peninsula agrees with species differences in foliage frost tolerance, not with vulnerability to freezing-induced xylem embolism.

Drought and frosts are major determinants of plant functioning and distribution. Both stresses can cause xylem embolism and foliage damage. The objective of this study was to analyse if the distribution of six common pine species along latitudinal and altitudinal gradients in Europe is related to their interspecific differences in frost tolerance and to the physiological mechanisms underlying species-specific frost tolerance. We also evaluate if frost tolerance depends on plant water status. We studied survival to a range of freezing temperatures in 2-year-old plants and assessed the percentage loss of hydraulic conductivity (PLC) due xylem embolism formation and foliage damage determined by needle electrolyte leakage (EL) after a single frost cycle to -15 °C and over a range of predawn water potential (ψpd) values. Species experiencing cold winters in their range (Pinus nigra J.F. Arnold, Pinus sylvestris L. and Pinus uncinata Raymond ex A. DC.) had the highest frost survival rates and lowest needle EL and soluble sugar (SS) concentration. In contrast, the pines inhabiting mild or cool winter locations (especially Pinus halepensis Mill. and Pinus pinea L. and, to a lesser extent, Pinus pinaster Ait.) had the lowest frost survival and highest needle EL and SS values. Freezing-induced PLC was very low and differences among species were not related to frost damage. Reduction in ψpd decreased leaf frost damage in P. pinea and P. sylvestris, increased it in P. uncinata and had a neutral effect on the rest of the species. This study demonstrates that freezing temperatures are a major environmental driver for pine distribution and suggests that interspecific differences in leaf frost sensitivity rather than vulnerability to freezing-induced embolism or SS explain pine juvenile frost survival.

Influence of physical and mechanical properties on the durability of limestone subjected to freeze-thaw cycles

The frost sensitivity of five French limestones (Massangis (MA), Lens (LS), Savonnières (SA), Saint-Maximin (MX) and Migné (MI)), with different physical and mechanical properties, was studied. The total porosity ranges from 10% to 35% and the uniaxial compressive strength ranges between 10 MPa and 60 MPa. The freeze-thaw tests were applied on the samples saturated in natural condition. During freeze-thaw cycles we recorded the evolution of temperature and volumetric strain of a specimen for each stone and after the freeze-thaw cycles, the weathering evolution in stone samples was monitored by measurement of different physical and mechanical parameters (porosity, P-wave velocity, fracture toughness, compressive strength and elastic static modulus). Two behaviors were observed: a volumetric expansion during freezing phase accompanied by a very important damage from the first cycle until the failure of specimen for MI and MX stones, and a volumetric contraction accompanied with a light damage for the high number of freeze-thaw cycle in the cases of MA, LS and SA. Following the freeze–thaw tests, the durability of stones was evaluated using a decay function model. The decay constant values determined from the evolution of P-wave velocity were correlated with different fresh stone properties. Contrary to generally accepted ideas, the correlation coefficients between the decay constant and total porosity or degree of saturation are very low. Porosity in natural condition seems to have the strongest influence on the decay constant. However, its negative impact can be offset by a bigger part of trapped porosity. The results indicate that it is possible to predict the frost damage of the stones, with a better level of confidence, from the ratio of the volume fraction of water to that of air rather than from only the total porosity or degree of saturation.

Intraspecific variation in response to magnitude and frequency of freeze-thaw cycles in a temperate grass.

Winter warming and its accompanying predicted decrease in snow pack for northern temperate regions may increase frost damage to plants induced by an increase in freeze-thaw cycles (FTCs) due to reduced insulation. FTC frequency, minimum temperature during freezing and pre-existing local adaptations potentially all influence site-specific plant responses to future climatic changes. Within a chamber experiment, frost sensitivity towards recurrent FTCs was determined in 12 Dactylis glomerata populations from various European sampling sites differing in temperature and precipitation. After winter hardening, plants were frozen at -4 and -8 °C at frequencies of one, three and seven FTCs within a 1-week treatment phase. The control was kept at 4.5 °C. Plant survival, leaf elongation, chlorophyll content and above-ground net primary productivity (ANPP) decreased with lower minimum temperatures and higher FTC frequencies, while lower freezing temperatures generally proved more influential than increased freezing frequencies. Plant survival rates correlated with the amount of annual precipitation at seed origin, as individuals from comparably drier sites exhibited higher survival rates. This response, however, was limited in its effect to low freezing temperatures (-8 °C) and low and medium freezing frequencies (1 and 3 FTCs). In the set of surviving plants, water availability at seed origin best explained the plants' growth responses to FTC treatment. The observed intraspecific variation emphasizes the ecological importance of potential local adaptations within a more variable future winter climate.

Winter warming effects on tundra shrub performance are species‐specific and dependent on spring conditions

Abstract Climate change‐driven increases in winter temperatures positively affect conditions for shrub growth in arctic tundra by decreasing plant frost damage and stimulation of nutrient availability. However, the extent to which shrubs may benefit from these conditions may be strongly dependent on the following spring climate. Species‐specific differences in phenology and spring frost sensitivity likely affect shrub growth responses to warming. Additionally, effects of changes in winter and spring climate may differ over small spatial scales, as shrub growth may be dependent on natural variation in snow cover, shrub density and cryoturbation. We investigated the effects of winter warming and altered spring climate on growing‐season performance of three common and widespread shrub species in cryoturbated non‐sorted circle arctic tundra. By insulating sparsely vegetated non‐sorted circles and parts of the surrounding heath with additional snow or gardening fleeces, we created two climate change scenarios: snow addition increased soil temperatures in autumn and winter and delayed snowmelt timing without increasing spring temperatures, whereas fleeces increased soil temperature similarly in autumn and winter, but created warmer spring conditions without altering snowmelt timing. Winter warming affected shrub performance, but the direction and magnitude were species‐specific and dependent on spring conditions. Spring warming advanced, and later snowmelt delayed canopy green‐up. The fleece treatment did not affect shoot growth and biomass in any shrub species despite decreasing leaf frost damage in Empetrum nigrum. Snow addition decreased frost damage and stimulated growth of Vaccinium vitis‐idaea by c. 50%, while decreasing Betula nana growth (p &lt; .1). All of these effects were consistent the mostly barren circles and surrounding heath. Synthesis. In cryoturbated arctic tundra, growth of Vaccinium vitis‐idaea may substantially increase when a thicker snow cover delays snowmelt, whereas in longer term, warmer winters and springs may favour E. nigrum instead. This may affect shrub community composition and cover, with potentially far‐reaching effects on arctic ecosystem functioning via its effects on cryoturbation, carbon cycling and trophic cascading. Our results highlight the importance of disentangling effects of winter and spring climate change timing and nature, as spring conditions are a crucial factor in determining the impact of winter warming on plant performance.

NMR-based Metabolomics to Study the Cold-acclimation Strategy of Two Miscanthus Genotypes.

Abiotic stress is a major cause of yield loss in plant culture. Miscanthus, a perennial C4 grass, is now considered a major source of renewable energy, especially for biofuel production. During the first year of planting in Northern Europe, Miscanthus was exposed to frost temperature, which generated high mortality in young plants and large loss of yield. One strategy to avoid such loss is to apply cold-acclimation, which confers on plants a better resistance to low temperature. The aim of this study is to describe the effect of a cold-acclimation period on the metabolome of two Miscanthus genotypes that vary in their frost sensitivity at the juvenile stage. Miscanthus × giganteus (GIG) is particularly sensitive to frost, whereas Miscanthus sinensis August Feder (AUG) is tolerant. Polar metabolite extraction was performed on Miscanthus, grown in non-acclimated or cold-acclimated conditions. Extracts were analysed by 1 H-NMR followed by multivariate statistical analysis. Discriminant metabolites were identified. More than 40 metabolites were identified in the two Miscanthus genotypes. GIG and AUG showed a different metabolic background before cold treatment, probably related to their genetic background. After cold-acclimation, GIG and AUG metabolomes remained different. The tolerant genotype showed notably higher levels of accumulation in proline, sucrose and maltose when subjected to cold. These two genotypes seem to have a different adaptation strategy in cold conditions. The studied change in the metabolome concerns different types of molecules related to the cold-tolerant behaviour of Miscanthus. Copyright © 2016 John Wiley & Sons, Ltd.

Distribution ranges and spring phenology explain late frost sensitivity in 170 woody plants from the Northern Hemisphere

AbstractAimCold events determine the distributional range limits of woody species. Despite global warming, the magnitude of late frost events in boreal and temperate regions is not expected to change. Hence, the risk for late spring frost damage of woody species may increase with an earlier onset of the growing season. Here, we investigated biogeographical, phenological and phylogenetic effects on late frost sensitivity.LocationEcological‐Botanical Gardens Bayreuth, Germany (49°55′45″ N, 11°35′10″ E).MethodsWe inspected 170 woody species in the Ecological‐Botanical Gardens from across the entire Northern Hemisphere for frost damage after an extreme late frost event in May 2011 (air temperature −4.3 °C after leaf unfolding of all species). Distribution range characteristics, climatic parameters of place of origin and phenological strategy were linked to sensitivity to the late frost event.ResultsThe northern distribution limit and the range in continentality across the distributional ranges correlated negatively with a taxon's late frost sensitivity (pseudo‐R2 = 0.42, pseudo‐R2 = 0.33, respectively). Sensitivity to the late frost event was well explained by the climatic conditions within species’ native ranges (boosted regression trees; receiver operating characteristic 0.737). Average (1950–2000) May minimum temperature in species’ native ranges was the main explanatory variable of late frost sensitivity (51.7% of explained variance). Phylogenetic relatedness explained additional variance in sensitivity to the late frost event. Sensitivity to the late frost event further correlates well with species phenological strategy. Frost‐tolerant species flushed on average 2 weeks earlier than frost‐sensitive species.Main conclusionsRange characteristics and the prevalent climatic parameters across species native ranges are strongly related to their susceptibility to late spring frost damage. Further, more late frost‐sensitive species unfolded their leaves later than more tolerant species and late frost tolerance is phylogenetically conserved. Thus, late frost sensitivity may challenge natural and human‐assisted migration of woody species under global warming.

Frost sensitivity of leaves and flowers of subalpine plants is related to tissue type and phenology

Summary Harsh abiotic conditions – such as low temperatures that lead to spring and summer frost events in high‐elevation and high‐latitude ecosystems – can have strong negative consequences for plant growth, survival and reproduction. Despite the predicted increase in episodic frost events under continued climate change in some ecosystems, our general understanding of the factors associated with frost sensitivity of reproductive and vegetative plant structures in natural plant communities is limited. The timing of growth and reproduction may be an important strategy by which plants can avoid frost. In this study, we experimentally investigated the frost sensitivity of eight long‐lived perennial herbaceous plant species from a subalpine ecosystem in the Colorado Rocky Mountains, USA. The study taxa represent four congeneric pairs from four flowering plant families; within each pair, there is a species with early and late growth and reproductive phenology. Thus, we control for evolutionary history – and therefore additional traits shared through common ancestry – to some degree, while examining the influence of phenology on frost sensitivity. Specifically, we compared frost sensitivity of vegetative and reproductive structures for each species and asked whether frost sensitivity was similar between species within congeneric pairs or, instead, was related to phenology (i.e. differences in the timing of growth and reproduction). For most species (6 of 8), flowers were more sensitive to frost than leaves. Within most congeneric pairs (3 of 4), the leaves of species with later phenology were significantly more sensitive to frost than the leaves of species with earlier phenology. For flowers, the later flowering species were more sensitive in two of the four congeneric pairs. Synthesis. This study contributes to our general understanding of factors related to interspecific differences in plant sensitivity to episodic frost events of naturally occurring species. The increased frost sensitivity of reproductive structures compared to vegetative structures may be a widespread pattern for long‐lived perennial plants. Furthermore, we find evidence for a trade‐off between phenology and frost sensitivity, whereby species with later phenology exhibit higher frost sensitivity compared to species with earlier phenology. These results have implications for plant populations, species interactions and ecological communities.

Dynamics of frost tolerance during regeneration in a mixed (pine–oak–juniper) Mediterranean forest

Key message The effect of unexpected low tempera- ture on coexisting species in inland locations was examined; frost tolerance simulation over a 2-year period was used to determine bottlenecks where com- petition can arise. Abstract The effect of frost events on natural regenera- tion of Mediterranean mixed forests under a scenario of climate change is not well known. The expected increase in mean annual temperature and the greater inter- and intra- annual variability in frosts occurrence can significantly damage natural regeneration leading to death, with a decisive effect on species composition and forest dynam- ics. We investigated seasonal variations in frost tolerance of three Mediterranean species (Pinus pinea, Quercus ilex and Juniperus oxycedrus) co-occurring in inland locations in Spain. Our aim was to assess seasonal inter-specific differences in frost sensitivity or tolerance. First, we applied the relative electrolyte leakage method (REL) to estimate the frost tolerance of these species every 3-4 weeks during the 9-month period in which frost events can occur in a year. Second, we explored the REL rela- tionship with environmental variables impacting frost acclimation/deacclimation, i.e., absolute minimum and maximum temperatures and photoperiod. Third, we built a REL model to predict seasonal variations in REL perfor- mance of young trees. We simulated REL through a 2-year period, thus defining seasonal bottlenecks in which the dynamics of regeneration can be affected by frost events. Our results showed contrasting behaviors between species, highlighting a greater sensitivity to cold of P. pinea com- pared to the other two species. The three species are most vulnerable in autumn; however, the different strategies to cope with unfavorable conditions adopted by Q. ilex and J. oxycedrus (e.g., stress tolerance and/or resprouting ability) give these species a competitive advantage over P. pinea.

Effects of environmental factors and management practices on microclimate, winter physiology, and frost resistance in trees.

Freezing stress is one of the most important limiting factors determining the ecological distribution and production of tree species. Assessment of frost risk is, therefore, critical for forestry, fruit production, and horticulture. Frost risk is substantial when hazard (i.e., exposure to damaging freezing temperatures) intersects with vulnerability (i.e., frost sensitivity). Based on a large number of studies on frost resistance and frost occurrence, we highlight the complex interactive roles of environmental conditions, carbohydrates, and water status in frost risk development. To supersede the classical empirical relations used to model frost hardiness, we propose an integrated ecophysiologically-based framework of frost risk assessment. This framework details the individual or interactive roles of these factors, and how they are distributed in time and space at the individual-tree level (within-crown and across organs). Based on this general framework, we are able to highlight factors by which different environmental conditions (e.g., temperature, light, flood, and drought), and management practices (pruning, thinning, girdling, sheltering, water aspersion, irrigation, and fertilization) influence frost sensitivity and frost exposure of trees.

Frost damage induced antioxidant enzymes changes in two cultivars of Prunus persica (L.) Batsch flowers

This study was undertaken to understand peach flowers response to frost damage and the relationship between frost damage and antioxidant enzyme activity in order to develop a criterion for the selecting the frost-resistant cultivars. For this purpose, antioxidant enzymes (catalase, peroxidase, and superoxide dismutase), and polyphenol oxidase activities, frost sensitivity index expressed as injured ovaries percent, and ECr (Relative electrical conductivity) of flowers at full bloom stage (F' Fleckinger) of two peach cultivars ('Takdaneh', and 'Sephid-Ghermez') exposed to freezing temperatures (-1.5, -2.5 and -3.5°C) were determined. The activities of antioxidant enzymes, such as catalase, superoxide dismutase, and peroxidase in 'Sephid-Ghermez' were increased or remained unchanged as temperature decreased. While for 'Takdaneh', the mentioned enzymes lost their activities from -2.5 to -3.5°C. Results suggested that the frost tolerance of the cultivar with lower injured ovaries is associated with lesser ion leakage, catalase, peroxidase, superoxide dismutase activity, and polyphenol oxidase activity. The different responses of enzymes may be one of the possible mechanisms of the differences in frost-sensitivities of the two peach cultivars.