Influence of the female flowering environment on autumn frost-hardiness of Picea abies progenies

Two experiments were designed to test possible effects of photoperiod and temperature during microsporogensis to anthesis on early autumn frost-hardiness of Picea abies progenies. Pollen lots were produced in phytotron rooms and used in crosses in a seed orchard. No biologically important differences in progeny performance were evident either between high and low temperature or between long and short-day treatments, and no significant interaction between photoperiod and temperature was found. In a third experiment, however, an effect of the environment during female flowering was obtained. Crosses performed in early spring (March) inside a heated greenhouse (short day, high temperature) produced progenies which were less hardy than their full-sibs reproduced from crosses indoors (long day, high temperature) and outdoors (long day, low temperature) in May. The most hardy siblings originated from the late-spring outdoor crosses. These results indicate that some stages in reproduction during female flowering, such as female meiosis, pollen tube growth, syngamy, early embryogenesis and embryo competition, may be sensitive to temperature and/or photoperiodic signals which can be transmitted to the progeny. We suspect that the altered performance of the progenies could be due to an activation of a regulatory mechanism affecting the expression of genes controlling adaptive traits. Both the present and earlier results have implications for the genetic interpretation of provenance differences in Norway spruce.     

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.     

Photoperiod cues and patterns of genetic variation limit phenological responses to climate change in warm parts of species’ range: Modeling diameter‐growth cessation in coast Douglas‐fir

The phenology of diameter‐growth cessation in trees will likely play a key role in mediating species and ecosystem responses to climate change. A common expectation is that warming will delay cessation, but the environmental and genetic influences on this process are poorly understood. We modeled the effects of temperature, photoperiod, and seed‐source climate on diameter‐growth‐cessation timing in coast Douglas‐fir (an ecologically and economically vital tree) using high‐frequency growth measurements across broad environmental gradients for a range of genotypes from different seed sources. Our model suggests that cool temperatures or short photoperiods can induce cessation in autumn. At cool locations (high latitude and elevation), cessation seems to be induced primarily by low temperatures in early autumn (under relatively long photoperiods), so warming will likely delay cessation and extend the growing season. But at warm locations (low latitude or elevation), cessation seems to be induced primarily by short photoperiods later in autumn, so warming will likely lead to only slight extensions of the growing season, reflecting photoperiod limitations on phenological shifts. Trees from seed sources experiencing frequent frosts in autumn or early winter tended to cease growth earlier in the autumn, potentially as an adaptation to avoid frost. Thus, gene flow into populations in warm locations with little frost will likely have limited potential to delay mean cessation dates because these populations already cease growth relatively late. In addition, data from an abnormal heat wave suggested that very high temperatures during long photoperiods in early summer might also induce cessation. Climate change could make these conditions more common in warm locations, leading to much earlier cessation. Thus, photoperiod cues, patterns of genetic variation, and summer heat waves could limit the capacity of coast Douglas‐fir to extend its growing season in response to climate change in the warm parts of its range.     

Freezing tolerance in two Norway spruce (Picea abies [L.] Karst.) progenies is physiologically correlated with drought tolerance

The goal of the present study was to investigate whether seedlings of Norway spruce (Picea abies [L.] Karst.) from a frost tolerant progeny (P2), were more drought tolerant than seedlings from a less frost tolerant progeny (P1). Progenies differing in freezing tolerance were identified by exposing seedlings in autumn in a large-scale trial to temperatures from -11 to -15 degrees C and scoring the degree of needle injury. Seedlings from P1 and P2 were grown from seeds for about 1 year under controlled conditions in a climatized growth room and were exposed to drought stress by withholding water for about 3 weeks. Drought caused reductions in biomass in both progenies but to a stronger extent in P1 than in P2. Seedlings of P2 were able to fully maintain root biomass. They also showed less water loss in different tissues. Decreases in quantum yield efficiency of photosystem II of dark-adapted plants occurred several days later in P2 than in P1. New proteins of molecular masses of 24.3 and 25.5 kDa appeared during drought stress. Since they occurred in both progenies a role of these proteins in progeny-related differences in drought performance is unlikely. Progeny 2 contained inherently higher superoxide dismutase and lower peroxidase activities than progeny 1. In conclusion, freezing and drought-tolerance respective -sensitivity were co-occurring traits in the spruce progenies studied here. Pre-existing high activities of enzymes protecting against oxidative stress in seedlings may have contributed to increase stress tolerance in P2 compared with P1.     

Effects of photoperiod and temperature on the termination of diapause in the univoltine seed wasp Eurytoma plotnikovi

Abstract Mummified pistachios containing fully grown diapause larvae of Eurytoma plotnikovi Nikol'skaya (Hym., Eurytomidae) were collected in early August and late September in coastal northern Greece and subjected to various photoperiod and temperature treatments, then maintained at 19 or 26°C and a long-day (LD 16:8 h), a changing, or a short-day (LD 10:14 h) photoperiod until pupation. In larvae of early August (beginning of diapause) subjected for 20 weeks to 19°C under a long, a changing, or a short photophase, followed by 19°C and a long photophase, 50% of the larvae pupated after 24, 18 and 13 weeks respectively. After exposure for 20 or even 12 weeks to a short photophase and low temperatures (10 or 4°C), pupation occurred after only 7–8 weeks and was more synchronous. The ranges of temperature for diapause development and post-diapause morphogenesis overlap. After exposure for 12 weeks to short days and low temperature, larvae of late September pupated much sooner under long days than under short days and sooner at 26° than at 19°C. E.plotnikovi depends on both temperature and photoperiod for diapause development, low temperature having a strong favourable effect on the earlier part and long day on the later part of diapause. In a few larvae of another pistachio seed wasp, Megastigmus pistaciae Walker, after a long enough period of low temperatures, diapause was terminated normally at 26°C and long days, or at 19°C and long or short days.     

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.     

A Norway spruce FLOWERING LOCUS T homolog is implicated in control of growth rhythm in conifers

Growth in perennial plants possesses an annual cycle of active growth and dormancy that is controlled by environmental factors, mainly photoperiod and temperature. In conifers and other nonangiosperm species, the molecular mechanisms behind these responses are currently unknown. In Norway spruce (Picea abies L. Karst.) seedlings, growth cessation and bud set are induced by short days and plants from southern latitudes require at least 7 to 10 h of darkness, whereas plants from northern latitudes need only 2 to 3 h of darkness. Bud burst, on the other hand, is almost exclusively controlled by temperature. To test the possible role of Norway spruce FLOWERING LOCUS T (FT)-like genes in growth rhythm, we have studied expression patterns of four Norway spruce FT family genes in two populations with a divergent bud set response under various photoperiodic conditions. Our data show a significant and tight correlation between growth rhythm (both bud set and bud burst), and expression pattern of one of the four Norway spruce phosphatidylethanolamine-binding protein gene family members (PaFT4) over a variety of experimental conditions. This study strongly suggests that one Norway spruce homolog to the FT gene, which controls flowering in angiosperms, is also a key integrator of photoperiodic and thermal signals in the control of growth rhythms in gymnosperms. The data also indicate that the divergent adaptive bud set responses of northern and southern Norway spruce populations, both to photoperiod and light quality, are mediated through PaFT4. These results provide a major advance in our understanding of the molecular control of a major adaptive trait in conifers and a tool for further molecular studies of adaptive variation in plants.     

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.     

Maternal Effects of Photoperiod and Food Level on Life History Characteristics of the Cladoceran Daphnia Pulicaria Forbes

The response of various life-history characteristics of Daphnia pulicaria to photoperiod and food concentration was measured in 16 combinations of maternal and offspring environments (long vs. short day, high vs. low food) in flow-through experiments. Response variables in offspring were time and survival to release of first offspring, clutch size and neonate mass in the first brood, mass of adult females after 30days and somatic growth rate during the course of the experiment. Most of these parameters were directly controlled by food concentration in the offspring environment, but maternal effects frequently modified the response. A long day length in the maternal environment resulted in a prolongation of the time to first clutch release in offspring similar to the direct effect of low food. Likewise, survival to maturation and female mass were affected by maternal photoperiod. Somatic growth rate and clutch size responded to combined effects of maternal food conditions and photoperiod. The laboratory results were used to predict the seasonal change of fecundity of Daphnia in the field. When data on clutch size are ordered in a sequence as the different combinations of maternal and offspring environment occur during the seasonal succession in a temperate lake, they show a bimodal distribution with a high peak in spring and a lower peak in fall. This pattern is consistent with field observations. We conclude that photoperiod and maternal effects are important factors influencing life history and population dynamics of Daphnia.     

Effect of temperature and photoperiod on the raffinose content of spruce roots

The influence of temperature and photoperiod on raffinose synthesis in spruce roots (Picea abies (L.) Karst.) was investigated under controlled environmental conditions in a phytotron. The raffinose content of the roots increased when the plants were subjected simultaneously to a change from long to short days and from summer-like day and night temperatures to a climate which was more than 10° C colder. Only a very slight raffinose accumulation resulted from a change of day-length or temperature alone, but a subsequent additional change of temperature or daylength, respectively, caused an increase in the raffinose content, yet only to half the amount found when both climate factors changed simultaneously. When the shoot was left under non-inducing conditions, but the root was cooled, the raffinose content increased in the root, but not in the shoot. The root was also capable of inducing raffinose if the shoot was cut off after a few days of cold adaptation of the whole plant. For all climate changes the sucrose content changed much less than the raffinose content. Induction of raffinose was comparable in mycorrhizal and in non-mycorrhizal roots.Abbreviations DW dry weight - LDC long day, cold - LDW long day, warm - SDC short day, cold - SDCLL short day, cold, low light - SDF short day, frost - SDW short day, warm This research was supported by the Bundesamt für Bildung und Wissenschaft and by the Swiss National Science Foundation.     

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.     

Environmental control of growth and development of Scrophularia marilandica

Summary Seedlings of Scrophularia marilandica were grown at different combinations of day/night temperature and photoperiod under controlled conditions. The species flowered in long days. The stems of plants grown at low temperature and short photoperiod failed to elongate. Treatment with gibberellic acid (GA₃) simulated the effect of increasing temperature and photoperiod and caused stem elongation in plants which would otherwise not have elongated. Application of GA₃ to plants grown at high temperature and long photoperiod resulted in increased stem elongation and flowering. The growth retardant (2-chloroethyl)trimethylammonium chloride (CCC) had little effect on rosette plants grown at low temperature and short photoperiod. Application of CCC to +GA₃ plants grown at a higher temperature and long photoperiod gave a significant increase in stem height. The interaction between temperature and applied GA is described in an experiment using plants grown at high and low temperatures for varying periods of time.This work was supported by National Science Foundation Grant GB 17483.     

Phytochrome action and frost hardening in black spruce seedlings

Black spruce [ Picea mariana (Mill.) B.S.P.] development is sensitive to photoperiod. To date the implication of photoperiod, and especially phytochrome, in the frost hardening process of black spruce has not been fully tested. Two light fluence rates, night interruption of darkness, and red vs far-red radiation treatments were applied to black spruce seedlings, followed by freezing at –6°C. Parallel to the freezing test, growth measurements, bud formation and the xylem water potential estimates of the seedlings were done. While dry weight accumulation depends on the irradiation energy level, bud formation and freezing tolerance are photoperiodically sensitive. Furthermore, bud formation and frost hardening are dependent upon whether phytochrome is in the active form or inactive form, as demonstrated by the positive effect of short days, far-red radiation and the reversal of the red effect by far-red radiation. Also, xylem water potential appears to be influenced by short day and far-red conditioning.     

Vegetative growth and frost hardiness of cloudberry (Rubus chamaemorus) as affected by temperature and photoperiod

The effect of photoperiod and temperature on growth and induction and development of frost hardiness in cloudberry ( Rubus chamaemorus L.) was examined in two experiments. The photoperiods were 8, 12 or 24 h and the temperatures were 18, 15, 12, 9, 4, 3, –3 or –4°C depending on the experiment. The level of hardiness was expressed as LT₆₆ or LT₅₀ (the lethal temperature for 66 or 50% of the plant material) for percentage of bud break and for the degree of coloring by triphenyltetrazolium chloride for rhizomes. The vegetative growth was clearly affected by daylength; petiole elongation, leaf growth, shoot dry weight and number of shoots per plant were all reduced under short days compared with long days. However, the photoperiod had no significant effect on hardening of buds or rhizomes. Hardening increased with successively decreasing temperatures. To get the maximum hardiness, plants had to be exposed to freezing temperatures.     

Environmental and Genetic Control of Dormancy in Picea abies

The effects of temperature, photoperiod and chilling on the leafing-out of Norway spruce, Picea abies (L.) Karst. were studied. High temperature promotes breakage of post-dormancy, long photoperiods having no such effect. Photoperiod and chilling cause the breakage of true dormancy. However, under field conditions, photoperiod will have no effect on leafing-out date in the spring. By use of clonal material it was possible to show substantial genetic differences between individuals in response to temperature and photoperiod. When the effect of clones was accounted for, treatments could be compared more precisely. Differences between clones were apparent in heat-sum required for leafing-out, in rapidity of response to favorable post chilling conditions, and in chilling requirement This latter quantity was given a new definition, applicable when both chilling and post chilling temperatures are controlled and specified. This is that period beyond which a further 10 days of chilling accelerates leafing-out by less than one day, i.e. the point at which the slope of the line relating days till leafing-out to chilling period, is equal to minus 0.10. Differences in leafing-out date were shown between provenances taken from throughout the range of Picea abies. These differences were related to latitude with provenances of high latitude leafing-out first.     

Growth and Dormancy in Norway Spruce Ecotypes (Picea abies) I. Interaction of Photoperiod and Temperature

Growth and dormancy as affected by photoperiod and temperature have been studied in Norway spruce ecotypes of different latitudinal and altitudinal origin. First-year seedlings were used. In all ecotypes apical growth cessation and terminal bud formation occurred within 2 weeks after exposure to SD at temperatures of 18 to 24°C. At lower temperatures or at near-critical photoperiods the response was delayed. The critical photoperiod for apical growth cessation varied from 21 hours in ecotype Steinkjer, Norway (64°N) to about 15 hours in ecotype Lankowitz, Austria (47°04′N). High-elevation ecotypes also had longer critical pholoperiods than low-elevation ecotypes from the same latitude. A detectable growth depression resulted from as little as 1 or 2 SDs of 10 hours, and with 4 or more SDs apical growth cessation took place. In contrast to the situation in the shoot, root growth was not affected by photoperiod. Accordingly, the top:root ratio is drastically affected by photoperiod. The critical photoperiod for cambial growth was shorter than that for apical growth in all ecotypes and cambial growth cessation was delayed for several weeks compared with cessation of apical growth. A transition to formation of late-wood tracheids with thick walls and narrow lumens took place upon exposure to SD. The photoperiodic effects were significantly modified by temperature, but the critical photoperiods were only slightly changed by temperature in the range of 12 to 24°C. However, a 10-hour “night” at 4°C caused growth cessation in continuous light in four ecotypes tested. Temperature optimum for apical growth under non-limiting photoperiods (24 hours) was 21°C in all ecotypes, but with little difference among 18,21 and 24°C. The Q₁₀ for apical growth was 3.5 in the temperature range 12 to 18°C. The growth potential as determined in 24-hour photoperiods was not significantly different among the various ecotypes except for one northern eco-type which was clearly inferior to the others. However, the growth of ecotype Steinkjer (64°N) was greatly suppressed even by the long midsummer days at 59°40′N, thus demonstrating the misleading impression one gets of the growth potential of northern ecotypes when they are moved southwards.     

EFFECT OF TEMPERATURE AND PHOTOPERIOD ON GROWTH AND DORMANCY OF BETULA PAPYRIFERA

The effects of day/night temperatures and photoperiod on the growth and dormancy of paper birch (Betula papyrifera) were studied in seedlings from different geographic origins. The response of Alaskan plants to temperature and photoperiod was distinctly different from other seed sources. Alaskan plants required very long days to prevent cessation of growth while plants from southern seed sources grew on photoperiods as short as 14 hr. Low night temperature (14 C) antagonized the promotive action of long photoperiods in Alaskan plants but had little effect in other seed sources. High day temperatures offset the inhibitory effect of the cool night to a lesser degree in Alaskan plants than in plants from other locations. Dormancy induced by short photoperiods was antagonized (relieved ?) to a lesser degree by high night temperatures in Alaskan birch than in other seed sources. Betula papyrifera var. humilis from Alaska may be an incipient species since its morphological traits are accompanied by adaptive physiological responses to its environment. These responses are as distinct as its morphological characteristics.     

The Cessation of Apical Growth in Latitudinal Ecotypes and Ecotype Crosses of Salix pentandra L

Apical growth cessation in seedling progenies of three latitudinalecotypes and ecotype crosses of Salix pentandra L. was investigatedunder controlled growth conditions and out-of-doors. The southernecotype (59° 40' N) was characterized by late growth cessationunder short day conditions, short critical photoperiod for growthcessation, and high light sensitivity; the northern ecotype(69° 39' N) by rapid growth cessation, long critical photoperiod,and low light sensitivity. The geographically intermediate ecotype(64° 28' N) had an intermediate photoperiodic response.The hybrid progenies were, however, closer to the southern thanto the northern parent ecotype indicating a tendency to favourinheritance of southern characters. Fluctuating temperatures(21 °C/9 °C and 18 °C/9 °C) induced growth cessationin the northern ecotype but not in the other ecotypes or ecotypecrosses with the exception of a few plants of the intermediateecotype and of two hybrid progenies. The time course of apicalgrowth cessation in various progenies grown out-of-doors at69° 39' N was similar to that observed under SD conditionsexcept that the differences between the northern ecotype andthe other ecotypes and crosses were greater.     

The environmental control of cold acclimation in apple

The role of photoperiod and temperature in the cold acclimation of living Haralson apple (Pyrus malus L.) bark was studied in the autumn under field conditions in Minnesota. Whole trees, or different parts of the same tree, were exposed to either natural conditions, artifically lengthened days, or artificially warmed nights, or they were subjected to manual leaf removal. The results indicate that acclimation occurs in two stages which are induced by short days and frost (or low temperature), respectively. Leaves were stimulated by short days to produce translocatable substance(s) which promoted cold acclimation of the living bark. Leaves of plants grown under long days were the source of a translocatable substance(s) which inhibited acclimation. The second stage of hardiness, induced by frost (or low temperature), did not involve translocatable factors.