Microclimate predicts frost hardiness of alpine Arabidopsis thaliana populations better than elevation

In mountain regions, topological differences on the microscale can strongly affect microclimate and may counteract the average effects of elevation, such as decreasing temperatures. While these interactions are well understood, their effect on plant adaptation is understudied. We investigated winter frost hardiness of Arabidopsis thaliana accessions originating from 13 sites along altitudinal gradients in the Southern Alps during three winters on an experimental field station on the Swabian Jura and compared levels of frost damage with the observed number of frost days and the lowest temperature in eight collection sites. We found that frost hardiness increased with elevation in a log‐linear fashion. This is consistent with adaptation to a higher frequency of frost conditions, but also indicates a decreasing rate of change in frost hardiness with increasing elevation. Moreover, the number of frost days measured with temperature loggers at the collection sites correlated much better with frost hardiness than the elevation of collection sites, suggesting that populations were adapted to their local microclimate. Notably, the variance in frost days across sites increased exponentially with elevation. Together, our results suggest that strong microclimate heterogeneity of high alpine environments can preserve functional genetic diversity among small populations. Synthesis: Here, we tested how plant populations differed in their adaptation to frost exposure along an elevation gradient and whether microsite temperatures improve the prediction of frost hardiness. We found that local temperatures, particularly the number of frost days, are a better predictor of the frost hardiness of plants than elevation. This reflects a substantial variance in frost frequency between sites at similar high elevations. We conclude that high mountain regions harbor microsites that differ in their local microclimate and thereby can preserve a high functional genetic diversity among them. Therefore, high mountain regions have the potential to function as a refugium in times of global change.     

Does ice crystal formation in buds explain growth disturbances in boron-deficient Norway spruce?

Loss of apical dominance in boron-deficient trees has been suggested to be due to frost damage of terminal buds and leaders. Excessive nitrogen (N) supply can exacerbate boron (B) deficiency by the dilution-effect. N may also have direct effects on winter hardiness. We studied frost hardening of buds of Norway spruce (Picea abies L. Karst.) in healthy-looking trees and in trees with growth disturbances. The effect of B and N on frost hardiness was studied in a factorial fertilisation experiment during cold acclimation. Frost hardiness was determined by differential temperature analysis (DTA) and scoring of visual damage. In a DTA profile of apical buds with a piece of stem, low-temperature exotherm (LTE) predicted bud injury, while two of the observed high-temperature exotherms and two of the observed intermediate-temperature exotherms were non injurious. Appearance of LTE followed changes in air temperature. The risk of frost damage was not affected by fertilisation treatments or previously observed growth disturbances. However, when the bud structure was deformed by severe B deficiency, the supercooling ability disappeared. Such buds are probably killed by freezing in nature and therefore, frost damage may play a secondary role in the development of growth disturbances.     

Effect of frost nights and day and night temperature during dormancy induction on frost hardiness, tolerance to cold storage and bud burst in seedlings of Norway spruce

For trees, the ability to obtain and maintain sufficient levels of frost hardiness in late autumn, winter and spring is crucial. We report that temperatures during dormancy induction influence bud set, frost hardiness, tolerance to cold storage, timing of bud burst and spring frost hardiness in seedlings of Norway spruce (Picea abies (L.) Karst.). Bud set occurred later in 12°C than in 21°C, and later in cool nights (7°C) than in constant temperature. One weekly frost night (−2.5°C) improved frost hardiness. Cool nights reduced frost hardiness early, but improved hardiness later during cold acclimation. Buds and stems were slightly hardier in 21°C than in 12°C, while needles were clearly hardier in 12°C. Cold daytime temperature, cool nights and one weekly frost night improved cold storability (0.7°C). Seedlings receiving high daytime temperatures burst buds later, and were less injured by light frost some days after bud burst.     

The importance of hardening and winter temperature for growth in mountain birch populations

Seedlings of five mountain birch populations (Betula pubescens Ehrh. ssp. czerepanovii) from Fennoscandia and Iceland were raised and grown at natural daylengths at Tromsø, Norway (69°N) and different temperatures during late summer and fall season, followed by winter temperature treatment at ambient and +4 °C above ambient temperatures at Bergen, Norway (60°N). The experiment took place during two seasons (2000/01 and 2001/02). The following summer shoot and biomass growth were reduced as a result of winter warming and subsequent premature dehardening in early flushing provenances and treatments. Biomass increased in plants grown at low hardening temperature when compared with high temperature treatment. As a conclusion, increased winter temperatures would tend to increase the risk of spring frost damage and reduce growth in birch seedlings, because the differences between the frost hardening and ambient temperatures are decreasing, and because the time from budbreak to dehardening is shortened. The results are discussed in relation to simultaneous experiments with frost hardiness in the same populations and treatments.     

Overwintering stress of Vaccinium vitis-idaea in the absence of snow cover

A snow manipulation experiment aimed to assess risks of direct freezing injury, freeze-induced dehydration and winter desiccation in the absence of snow cover on lingonberry (Vaccinium vitis-idaea). Frames with sheet-plastic sides and removable lids were used in this experiment for two purposes: to prevent accumulation of snow in mid-winter and to provide extra heat during early spring. Leaves were analyzed for frost hardiness, tissue water content and osmotic concentrations, and photoinhibition (Fv/Fm) during the period from the 10th of February to the 7th of April. The natural snow accumulation was low indicated by a minor difference in minimum temperatures between the frame treatment and naturally snow-covered plots. The heating effect of the frames started gradually at the end of February along with increasing solar elevation angles, and was highest at the beginning of April. Frost hardiness peaked in March as a consequence of cold periods, but it was practically lost by the beginning of April. Tissue water content decreased gradually at first, becoming greatly decreased later due to the extra heat. In accordance, the tissue osmotic concentrations increased first gradually, followed by a dramatic increase. Photoinhibition increased uniformly with increasing solar radiation, but at the end showed a sharp increment within a few days, obviously also indicating the effect of heating. It was concluded that neither lethal freezing stress nor significant freeze-induced dehydration occurred during the experiment. However, plants that overwintered without snow suffered from severe winter desiccation injuries due to the combination of solar heat and frozen soil. Although the desiccation stress was possibly a lethal factor, it was preceded by long-term and continued photoinhibition. It was concluded that during overwintering, chamaephyte species may suffer from both freezing and winter desiccation in the absence of protecting snow cover. However, during mild winters provided by climatic change scenarios, the risk of winter desiccation will be more probable. In relation to the future climate, it was concluded that winter desiccation and photoinhibition may develop gradually during a snowless winter and would, even if they did not reach a lethal level by themselves, possibly reduce frost hardiness.     

Recovery of photosynthetic capacity in <Emphasis Type="Italic">Vaccinium vitis</Emphasis>-<Emphasis Type="Italic">idaea</Emphasis> during mild spells in winter

Recent studies suggest that evergreen plants may maintain their photosynthetic capacity through the winter. Since mild winters are predicted to be more frequent in the future, the metabolic activity of plants is also likely to increase. The aim of the present study was to assess how various environmental factors, such as temperature, photoperiod and preceding frost, affect the recovery of photosynthesis during a mild spell in winter. The recovery of photosynthesis was studied in a series of growth chamber experiments where the overwintering of lingonberry (Vaccinium vitis-idaea) was interrupted by an intermittent warm spell of 1 week during different phases of winter. Rapid activation was observed in all the experiments during the first 3–4 days. No obvious effects of the phase of winter or photoperiod on the recovery of photosynthesis were observed, but a severe freezing treatment prior to the warm spell retarded the recovery significantly. Once recovered, however, lingonberry was able to maintain high rates of photosynthesis even at near-freezing temperatures, which prevail in their natural sub-nivean environment. The apparent quantum yield of photosynthesis remained high through the winter for lingonberry. This may prove advantageous for evergreen dwarf shrubs which overwinter in dim environments under snow.     

Ultrastructure of cells in the cambial region during winter hardening and spring dehardening in Salix dasyclados Wim. grown at two nutrient levels

Summary The ultrastructure of cells in the cambial region of Salix dasyclados Wim. (clone 78056) was studied during the development of winter hardiness and the onset of cambial activity in spring. Plants were grown at relative growth rates (R_G) of 8% and 12% respectively, resulting in different nitrogen content in the stems. Frost hardiness of the plants was estimated by standardized freezing tests. Plants with a higher nitrogen status ceased growth later and started re-growth earlier in spring than plants with lower nitrogen content. Differences in ability to withstand low temperatures during autumn and spring were found between plants grown in the two nutrient treatments. During the development of frost hardiness in the autumn, the number of meristematic cells in the cambial region decreased. The cessation of meristematic activity was accompanied by cell wall thickening and ultrastructural changes in the cells. Frost hardiness increased from the ability to survive -6° C in October to survival of -80° C at the beginning of December. From November to February the cambial region comprised a layer of 2–3 thick-walled cells with conspicuous ultrastructural features. Starch accumulated in plastids in September, decreased during November to March and then increased again in accordance with changes of frost hardiness. Onset of cambial activity began between the end of March and the beginning of April, as shown by increased vacuolization of meristematic cells and mitotic activity. By April, the starch content had increased and lipolysis was observed. Frost hardiness had decreased, and plants with low and high nitrogen content were able to survive -15° C and -10° C, respectively. After budburst, all axillary shoot parts were damaged at temperatures below-3° C.Abbreviations Cz cambial zone - ER endoplasmic reticulum - Lb lipid body - m mitochondrion - Mm multimembraneous structure - Ms myelin-like structure - n nucleus - p plastid - Pb protein body - Pc pit cells - Ph phloem - Pd plasmodesmata - Pl plasmalemma - pl protective layer - Pt plasmatubules - Pw primary wall - Sw secondary wall - s starch - t tannins - v vacuole - K vessel - X xylem - Scale bars 1 urn     

Long and Short Term Development of Frost Hardiness in Pinus silvestris, and Heavy Particle Adenosine Triphosphatase

The effect of different growth temperatures, of transfer between them, and of changes in outside temperature on frost hardiness and ATPase activity of Scotch pines (Pinus silvestris L.) were studied. Plants which had been grown in the greenhouse and transported to outside “remembered” something of their earlier growing circumstances during a long period. They differed from the plants continuously grown outside in the level of hardiness, although changes in temperature caused similar fluctuations in the hardiness of both groups. It is evident that two mechanisms are present, the one causing a long term determination of the level of frost hardiness obtainable, the other causing a short term adaption. The heavy particle ATPase activity as investigated below 20°C grouped itself according to the main temperature groups of the experiment. Above 30°C, the pretreatments had given rise to differences within the temperature groups. The level of the ATPase activity increased as the growing season came closer.     

Frost tolerance and biochemical changes during hardening and dehardening in contrasting white clover populations

Successful winter survival of perennial plants, like white clover, is dependent on proper timing of both hardening and dehardening. The purpose of this study was to investigate the regulation of these processes in two cultivars (AberCrest and AberHerald) and two Norwegian ecotypes (Særheim collected at 58°46′N lat. and Bodø at 67°20′N lat.) of white clover (Trifolium repens L.). For hardening and dehardening, plants were exposed to controlled temperature conditions and frost hardiness of stolons was tested by programmed freezing at the rate of 3°C per hour. In addition, stolons were analysed for starch, soluble sugars and soluble amino acids. Cultivars AberCrest and AberHerald, selected for growth at low temperature and winter hardiness in the United Kingdom, were significantly less hardy than the Norwegian populations. After six weeks of hardening (2 weeks at 6°C and 4 weeks at 0.5°C), estimated LT₅₀ values were ?13.8, ?13.0, ?17.8 and ?20.3°C for AberCrest, AberHerald, Saerheim and Bodø, respectively. The rate of dehardening increased with increasing temperature. At low temperature (6°C), the northern ecotype from Bodø was more resistant to dehardening than AberHerald. However, at 18°C the absolute rate of dehardening (°C day^?1) was twice as high in Bodø as in AberHerald plants. Stolon elongation during dehardening was initiated at lower temperatures in AberHerald than in plants of the Bodø ecotype. The content of total soluble sugars, sucrose and the amino acids proline and arginine were significantly higher in hardy plants of Bodø than in those of AberHerald. Sucrose levels decreased during dehardening and correlations between sucrose content and LT₅₀ during this process were statistically highly significant for both Bodø and AberHerald. The least hardy populations of white clover were characterized by thick stolons, long internodes and large leaves.     

Genetic analysis of frost hardiness traits in tuber-bearingSolanum species

The inheritance of frost hardiness and cold acclimation potential traits was studied in three segregating populations derived from a cross betweenSolanum commersonii Dun. PI 243503 (cmm) andSolanum cardiophyllum Lindl., PI 184762 (cph), two parental genotypes with contrasting frost hardiness and cold acclimation potential. The levels of frost hardiness and cold acclimation potential were expressed as the LT₅₀, the temperature at which 50% of the cells in leaf discs were killed, as measured by the ion leakage method, following a controlled freeze test There was considerable variation in both frost hardiness and cold acclimation potential in all three segregating populations (F₁ F₁ xcmm, and F₁ xcph). Frost hardiness and cold acclimation potential were not correlated, suggesting that these two traits are under independent genetic control. The analysis of generation means indicated that the variation for both traits could be best explained by an additive-dominance model, with additive gene effects the most important Broad-sense heritability was 0.73 and 0.74 in the F₁ population, for frost hardiness and cold acclimation potential, respectively, and was 0.85 for either trait in the F₁ xcmm population, indicating that these two traits are highly inheritable. Our results suggest that it should be possible to incorporate the frost hardiness and cold acclimation traits from S.commersonii into cultivated potato species.     

Influence of differences in <Emphasis Type="Italic">Ppd</Emphasis> genes on agronomic indicators of soft winter wheat

The dominant alleles of the Ppd genes tend to reduce the length of the time to heading, decrease winter hardiness and frost resistance at the end of winter, and also promote a significant growth in yield and growth in individual components of the yield. In terms of the degree of reduction of winter hardiness and frost resistance in years with severe winters and the increase in the yield in years with mild wintering conditions, the dominant alleles may be arranged in the following sequence: Ppd-Ala — Ppd-Bla — Ppd-Dla. In tall-growing genotypes the effects of the Ppd genes are directed towards reducing the height of the plant, while in intermediate-height genotypes, towards increasing the plant height.     

Seasonality of cavitation and frost fatigue in Acer mono Maxim.

Although cavitation is common in plants, it is unknown whether the cavitation resistance of xylem is seasonally constant or variable. We tested the changes in cavitation resistance of Acer mono before and after a controlled cavitation–refilling and freeze–thaw cycles for a whole year. Cavitation resistance was determined from ‘vulnerability curves’ showing the percent loss of conductivity versus xylem tension. Cavitation fatigue was defined as a reduction of cavitation resistance following a cavitation–refilling cycle, whereas frost fatigue was caused by a freeze–thaw cycle. A. mono developed seasonal changes in native embolisms; values were relatively high during winter but relatively low and constant throughout the growing season. Cavitation fatigue occurred and changed seasonally during the 12‐month cycle; the greatest fatigue response occurred during summer and the weakest during winter, and the transitions occurred during spring and autumn. A. mono was highly resistant to frost damage during the relatively mild winter months; however, a quite different situation occurred during the growing season, as the seasonal trend of frost fatigue was strikingly similar to that of cavitation fatigue. Seasonality changes in cavitation resistance may be caused by seasonal changes in the mechanical properties of the pit membranes.     

Use of intraspecific variation in thermal responses for estimating an elevational cline in the timing of cold hardening in a sub‐boreal conifer

To avoid winter frost damage, evergreen coniferous species develop cold hardiness with suitable phenology for the local climate regime. Along the elevational gradient, a genetic cline in autumn phenology is often recognised among coniferous populations, but further quantification of evolutionary adaptation related to the local environment and its responsible signals generating the phenological variation are poorly understood. We evaluated the timing of cold hardening among populations of Abies sachalinensis, based on time series freezing tests using trees derived from four seed source populations × three planting sites. Furthermore, we constructed a model to estimate the development of hardening from field temperatures and the intraspecific variations occurring during this process. An elevational cline was detected such that high‐elevation populations developed cold hardiness earlier than low‐elevation populations, representing significant genetic control. Because development occurred earlier at high‐elevation planting sites, the genetic trend across elevation overlapped with the environmental trend. Based on the trade‐off between later hardening to lengthen the active growth period and earlier hardening to avoid frost damage, this genetic cline would be adaptive to the local climate. Our modelling approach estimated intraspecific variation in two model components: the threshold temperature, which was the criterion for determining whether the trees accumulated the thermal value, and the chilling requirement for trees to achieve adequate cold hardiness. A higher threshold temperature and a lower chilling requirement could be responsible for the earlier phenology of the high‐elevation population. These thermal responses may be one of the important factors driving the elevation‐dependent adaptation of A. sachalinensis.     

Inheritance of autumn frost hardiness in Pinus sylvestris L. seedlings

Summary Inheritance of frost hardiness was analysed making use of a 12×12 incomplete factorial mating design. Owing to space limitations only 59 families could be tested in four experiments. To link the four experiments, some families were common to two or more experiments. The seedlings were grown in climate chambers under conditions inducing autumn hardening. The plants were exposed to a freezing temperature of –10 °C for three hours at night lengths of 11–13 h. A statistical model was developed for analyses of variance of our data. The genetic variation and the variation due to the cultivation regimes during autumn hardening were of the same magnitude. The additive effects were the most important ones for induction of frost damage. No interaction following long-distance crossing was noted. Mixed model equations were used for ranking of the parents. The results obtained support a polygenic inheritance of frost hardiness. The large within-population variation offers good opportunities for hardiness breeding.     

Interactions of low temperature, water stress, and short days in the induction of stem frost hardiness in red osier dogwood

The induction of stem frost hardiness by low temperature, water stress, short days, and their combinations in 2- and 4-month-old growing dogwoods (Cornus stolonifera) were investigated. When plants were subjected to more than one factor, the increased hardiness was the sum of the effects of the individual factors involved. No interactions among these factors on hardiness were observed during a 3-week treatment. Results indicate that low temperature, water stress, and short days initially trigger independent frost-hardening mechanisms. Plant ages significantly influenced the change in low temperature-induced frost hardiness, but not the water stress or short day-induced frost hardiness.     

Will loss of snow cover during climatic warming expose New Zealand alpine plants to increased frost damage?

If snow cover in alpine environments were reduced through climatic warming, plants that are normally protected by snow-lie in winter would become exposed to greater extremes of temperature and solar radiation. We examined the annual course of frost resistance of species of native alpine plants from southern New Zealand that are normally buried in snowbanks over winter (Celmisia haastii and Celmisia prorepens) or in sheltered areas that may accumulate snow (Hebe odora) and other species, typical of more exposed areas, that are relatively snow-free (Celmisia viscosa, Poa colensoi, Dracophyllum muscoides). The frost resistance of these principal species was in accord with habitat: those from snowbanks or sheltered areas showed the least frost resistance, whereas species from exposed areas had greater frost resistance throughout the year. P. colensoi had the greatest frost resistance (−32.5°C). All the principal species showed a rapid increase in frost resistance from summer to early winter (February–June) and maximum frost resistance in winter (July–August). The loss of resistance in late winter to early summer (August–December) was most rapid in P. colensoi and D. muscoides. Seasonal frost resistance of the principal species was more strongly related to daylength than to temperature, although all species except C. viscosa were significantly related to temperature when the influence of daylength was accounted for. Measurements of chlorophyll fluorescence indicated that photosynthetic efficiency of the principal species declined with increasing daylength. Levels of frost resistance of the six principal alpine plant species, and others measured during the growing season, were similar to those measured in tropical alpine areas and somewhat more resistant than those recorded in alpine areas of Europe. The potential for frost damage was greatest in spring. The current relationship of frost resistance with daylength is sufficient to prevent damage at any time of year. While warmer temperatures might lower frost resistance, they would also reduce the incidence of frosts, and the incidence of frost damage is unlikely to be altered. The relationship of frost resistance with daylength and temperature potentially provides a means of predicting the responses of alpine plants in response to global warming.     

The Influence of Photoperiod and Temperature on the Development of Frost Hardiness in Seedlings of Pinus silvestris and Picea abies

The influence of short days and low temperature on the development of frost hardiness in seedlings of Scots pine (Pinus silvestris L.) and Norway spruce [Picea abies (L.) Karst.], grown for 6 months in glasshouses and climate chambers, was investigated. The degree of hardiness was estimated by freezing the shoots of the seedlings to predetermined temperatures. After 8 weeks in a glasshouse the viability of the seedlings was determined by establishing bud flushing. The most effective climate for the development of frost hardiness was short days (SD) and low temperature (2°C); the next most effective was SD and room temperature (20°C). However, long days (LD) and low temperature also had a marked effect on the development of hardiness. A combination of 3 weeks’treatment with SD and 20°C, and 3 weeks with SD and 2°C gave the same results as 6 weeks with SD and 2°C. The results clearly demonstrate the importance of the photoperiod prior to low temperature for the development of frost hardiness. In conclusion both short days and low temperature induce frost hardiness development. Probably this occurs by initiation of different processes in the two cases. The degree of frost hardiness development appears to depend on the sum of these different processes and on the timing between them.     

Studies of Frost Hardiness in Woody Plants. II. Effect of Temperature on Hardening

The effect of temperature on hardening was studied at temperatures ranging from 0° to −20° using twigs of willow and poplar. In October and in late April when the twigs are not very frost hardy, hardening at 0° produced a considerable increase in their frost hardiness, although the effectiveness of hardening at 0° decreased with a decrease in the environmental temperature. In twigs which could withstand continuous freezing without injury, hardening at −3° to −5° was most effective in increasing the frost hardiness of the twigs. Below −20°, only negligible increase was observed either in frost hardiness or sugar content.

The rate of starch to sugar conversion differed remarkably in different twig tissues. The starch in xylem was more slowly converted to sugar than that in the cortex. The optimum temperature for converting starch into sugar during frost hardening was also found to be −3° to −5°. In addition, the greater the effectiveness of the hardening treatment, the greater the rate of conversion from starch to sugar. The frost hardiness of a twig is closely related to the sugar content of the twig, especially in the xylem.

     

The effects of long-term elevation of air temperature and CO on the frost hardiness of Scots pine

The frost hardiness of 20 to 25-year-old Scots pine (Pinus sylvestris L.) saplings was followed for 2 years in an experiment that attempted to simulate the predicted climatic conditions of the future, i.e. increased atmospheric CO₂ concentration and/or elevated air temperature. Frost hardiness was determined by an electrolyte leakage method and visual damage scoring on needles. Elevated temperatures caused needles to harden later and deharden earlier than the controls. In the first year, elevated CO₂ enhanced hardening at elevated temperatures, but this effect disappeared the next year. Dehardening was hastened by elevating CO₂ in both springs. The frost hardiness was high (相似文献   

Local adaptations to frost in marginal and central populations of the dominant forest tree Fagus sylvatica L. as affected by temperature and extreme drought in common garden experiments

Local adaptations to environmental conditions are of high ecological importance as they determine distribution ranges and likely affect species responses to climate change. Increased environmental stress (warming, extreme drought) due to climate change in combination with decreased genetic mixing due to isolation may lead to stronger local adaptations of geographically marginal than central populations. We experimentally observed local adaptations of three marginal and four central populations of Fagus sylvatica L., the dominant native forest tree, to frost over winter and in spring (late frost). We determined frost hardiness of buds and roots by the relative electrolyte leakage in two common garden experiments. The experiment at the cold site included a continuous warming treatment; the experiment at the warm site included a preceding summer drought manipulation. In both experiments, we found evidence for local adaptation to frost, with stronger signs of local adaptation in marginal populations. Winter frost killed many of the potted individuals at the cold site, with higher survival in the warming treatment and in those populations originating from colder environments. However, we found no difference in winter frost tolerance of buds among populations, implying that bud survival was not the main cue for mortality. Bud late frost tolerance in April differed between populations at the warm site, mainly because of phenological differences in bud break. Increased spring frost tolerance of plants which had experienced drought stress in the preceding summer could also be explained by shifts in phenology. Stronger local adaptations to climate in geographically marginal than central populations imply the potential for adaptation to climate at range edges. In times of climate change, however, it needs to be tested whether locally adapted populations at range margins can successfully adapt further to changing conditions.