Direct relation between growth and frost hardening in cabbage leaves

Potted cabbage plants were grown in growth chambers at 25° day and 15° night and hardened successively at 5, 0, and −3°. Leaf growth was determined by measuring leaf area, hardiness by freezing at a series of temperatures and determining percent survival. Leaf growth increased progessively with leaf number, reaching a maximum rate of growth and final area in the tenth and eleventh leaves when the plants become potbound. Leaf growth continued at hardening temperatures of 5 or 0°, the Q₁₀ being 2.0 to 2.5. Ability to harden also increased with leaf number, paralleling the growth rate of the leaves just before hardening as well as the growth rate and the total growth during hardening. The above results were similar whether prolonged (several weeks) or brief (24 hr) hardening was utilized.     

The structure and hardening status of Scots pine needles at different potassium availability levels

 Scots pine (Pinus sylvestris L.) seedlings were exposed to three levels of potassium (low, medium and high) and their needle morphology, the cellular structure of the mesophyll and transfusion parenchyma, and the hardening status of the mesophyll cells were examined by light and transmission electron microscopy. The higher the potassium level the greater was the growth of the needles. The area of the mesophyll tissue increased slightly and those of the phloem, xylem and resin ducts decreased in the needles of the seedlings grown at the high K level. Cellular studies revealed that swelling of the chloroplast thylakoids, accumulation of starch in the chloroplasts, translucency of the cytoplasm and plasmolysis in the mesophyll cells were related to a low K level. The hardening status of the mesophyll cells was enhanced after 5 weeks of hardening treatment at high K as seen in changes in chloroplast shape and position and the structure of the endoplasmic reticulum, but the pines showed no major differences in the hardening status of their mesophyll cells between K levels at the end of the experiment, after 9 weeks of hardening. Frost resistance, as shown by the electrolyte leakage test, was nevertheless highest at low K, being related to the increase in the concentration of polyamine putrescine at this potassium level. Received: 23 December 1997 / Accepted: 30 March 1998     

Sterols and frost hardening of winter rape

Winter rape ( Brassica napus L., var. olifera cv. Górczanski) seedlings were exposed to hardening conditions and the content and composition of free sterols as well as the ratio of free sterols to total phospholipids were determined. There was a reduction in free sterol content in the leaves at the most advanced stage of hardening. The ratio of free sterol to total phospholipids was significantly reduced by hardening due to a decrease in the level of the former and an increase in that of the latter compounds. There was a negative correlation between this ratio and the temperature at which half of the seedlings died. Thus, adaptation of membranes to temperature takes place also at the level of sterol-phospholipid interactions. Exposing seedlings already hardened to freezing temperatures caused injury higher than 50%, and brought about a drastic increase in the level of free sterols and an elevation in the ratio of free sterols to phospholipids. The results are discussed in terms of a possible role of the molecular architecture of membranes in surviving at subzero temperatures.     

On the mechanisms of frost injury and frost hardening of spruce chloroplasts

Hill reaction and noncyclic photophosphorylation of isolated class C chloroplasts of spruce (Picea abies (L.) Karst.), as well as ¹⁴CO₂ fixation by whole needles at constant laboratory conditions proceeded at high rates during spring and early summer, declined during late summer and autumn by about 60%, remained at this level during winter, and recovered quickly in early spring. During summer, the whole needles proved to be frost labile, since after exposure to-20°C and careful thawing, fast chlorophyll degradation occurred. In addition, only photosynthetically inactive chloroplasts could be isolated from those precooled needles. On the contrary, during winter the photochemical activities of plastids from freshly harvested needles did not differ from those of artificially frozen-thawed needles. When isolated spruce chloroplasts were exposed to the same subfreezing temperatures as the whole needles, no influence of freezing on the photochemical activities was observed, irrespective of whether the plastids were isolated from frost sensitive or frost hardened needles. It is concluded that frost damage to spruce chloroplasts is due to an attack of membrane toxic compounds or lytic enzymes which were liberated upon freezing from more labile compartments. Frost hardening of the chloroplasts, as determined by the stability of chlorophyll after exposure of the needles to low temperatures, as well as by the isolation of photosynthetically active chloroplasts from such precooled needles, appeared to depend at least on 2 processes: (i) an alteration of the composition of the photosynthetically active membranes and (ii) and additional stabilization of these membranes by protecting substances. The first process was indicated by a large increase (decrease) of the capability of isolated chloroplasts for PMS-mediated photophosphorylation which accompanied natural or artificial frost hardening (dehardening). Production of cryoprotecting compounds was suggested by a significant higher stability against NaCl observed with class C chloroplasts isolated from frost hardened needles as compared to that of plastids from frost labile material. The decrease of the capability for both, the ferricyanide dependent photoreactions of the plastids and the CO₂ fixation by whole needles, which was observed during the frost hardening phase, cannot be due to freezing injuries; it rather appears to be a consequence of the frost hardening process.     

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.     

Effects of frost hardening, dehardening and freezing stress on in vivo chlorophyll fluorescence of seedlings of Scots pine (Pinus sylvestris L.)

Abstract. The kinetics of in vivo chlorophyll fluorescence of photosystem II (PS II) was measured at room temperature and 77 K during frost hardening of seedlings of Scots pine (Pinus sylvestris L.), and after exposure of frost-hardened shoots to sub-freezing temperatures. A more pronounced decrease in variable fluorescence yield for the upper exposed than for the lower shaded surface of the needles suggested that some photoinhibition occurred during prolonged frost hardening at 50 μmol photons m^?2 s^?1 and 4°C. Reversible inhibition of photosynthesis after exposure to sub-freezing temperatures was initially manifested as an increase of steady-state energy-dependent fluorescence quenching (q_E) and a reduction in the rate of O₂ evolution. Further inhibition after treatment at still lower temperatures caused a progressive decline of steady-state photochemical quenching (q_Q) and the rate of O₂ evolution, whereas q_E remained high. This implies an inactivation of enzymes in the photosynthetic carbon reduction cycle decreasing the consumption of ATP and NADPH, which is likely to cause an increase of membrane energization and a reduction of the primary electron acceptor (Q_A) of PS II. Alternatively, the changes in q_Q and q_E might be attributed to an inhibition of photophosphorylation. Severe, irreversible damage to photosynthesis resulted in a suppression of q_E and of variable fluorescence yield, probably because the photochemical efficiency of PS II was impaired. Changes in the fast fluorescence kinetics at room temperature after severe freezing damage were interpreted as an inhibition of the electron flow from Q_A to the plastoquinone pool. It is suggested that irreversible freezing injury to needles of frost-hardened P. sylvestris causes damage to the Q_B,-protein.     

Effects of growth stage and hardening conditions on the association between frost resistance and the expression of the cold-induced protein COR14b in barley

Sowing date, being determinant for growth stage, may play a decisive role in optimising freezing resistance of winter annual plants. In cereal species, in spite of the abundant literature analysing the factors responsible for the acquisition of frost resistance through the cold hardening process, the involvement of the growth stage per se, has been seldom considered, especially at the earlier vegetative phases. In this work the contribution of growth stage in determining resistance to freezing temperature has been analysed in field and growth chamber experiments using winter and spring barley cultivars exposed to different hardening conditions. Field damage was assessed twice during winter on plants sown at three different dates. In the growth chamber experiments several acclimation treatments at 11/7 and/or 3/1 °C (day/night) were simulated. In both field and laboratory experiments the development of cold acclimation was monitored by means of a COR14b specific antibody, since in previous studies the expression of COR14b was found genetically linked to frost resistance. The lowest resistance, found in the youngest plants and in spring cultivars, however, was not always associated with the lowest level of COR14b accumulation. COR14b accumulation correlated with frost resistance at the earlier field sampling date and in plants grown at 11/7 °C. In a following phase of the hardening process (second sampling in field and 4 weeks at 3/1 °C in growth chamber) the accumulation of COR14b was independent of plant stage and genotype, showing no association with freezing resistance. Results suggest that growth stage is crucial for the achievement of maximal resistance in barley, but not for COR14b expression.     

Sap flow in Scots pines growing under conditions of year-round carbon dioxide enrichment and temperature elevation

Starting in rrrr, individual trees of Scots pine (Pinus sylvestris L.) aged 30 years were grown in closed-top chambers and exposed to normal ambient conditions (CON), elevated CO₂ (Elev. C), elevated temperature (Elev. T) and a combination of elevated CO₂ and temperature (Elev. C + T). Using the constant-power heat balance method, sap flow was monitored simultaneously in a total of 16 trees, four for each treatment, over a 32 d period (after the completion of needle expansion and branch elongation in 1997). An overall variation in diurnal sap flow totals (F_t) was evident during the period of measurement (days 167–198, 1997) regardless of the treatments, with a range from 0·15 to 2·82 kg tree^–1 d^–1. Elev. C reduced F_t by 4·1–13·7% compared with CON on most days (P varies from 0·042 to 0·108), but slightly increased it on some days (P≥ 0·131), depending on the weather conditions. Although the decrease in F_t caused by Elev. C was statistically significant on only a few days (P≤ 0·042), the cumulative F_t for the 32 d decreased by 14·4% (P = 0·047), indicating that Elev. C may have an important influence on seasonal water use of the Scots pine. Analysis of the diurnal courses of sap flow combined with corresponding weather factors indicated that the CO₂-induced decrease in F_t could be largely attributed to an increase in stomatal sensitivity to vapour pressure deficit (VPD), whereas the CO₂-induced increase in F_t related to an increase in stomatal sensitivity to low light levels. Elev. T increased F_t by 11·2–35·6% throughout the measuring period and the cumulative F_t for the 32 d by 32·5% (P = 0·019), which could be largely attributed to the temperature-induced increase in current-year needle area and decrease in stomatal sensitivity to high levels of VPD. There were no significant interactive effects of CO₂ and temperature on sap flow, so that Elev. C + T had approximately the same F_t as Elev. T and similar diurnal patterns of sap flow, suggesting that the temperature factor played a dominant role in the case of Elev. C + T.     

Dormancy development during cold hardening of in vitro cultured Malus domestica Borkh. plants in relation to their frost resistance and cryotolerance

The development of dormancy, frost resistance and cryotolerance of in vitro apple plants (Malus domestica Borkh.), cv. Greensleeves during their exposure to cold hardening was studied. In vitro cultures were cold hardened at 4°C under a short photoperiod up to 25?weeks. The dormancy status, non-structural saccharides, proline, water content and frost resistance were evaluated for optimization of cryopreservation. According to regrowth tests, in vitro cultures exhibited endogenous dormancy after the maximal frost resistance was reached. The highest regeneration ability of shoot tips after cryopreservation by encapsulation–dehydration method coincided with the period of the plant’s dormant state and maximum of frost resistance. All studied saccharides and proline exhibited the maximal values at the beginning of cold hardening and/or the dormancy phase. Contrary to the accumulation of saccharides and proline, water content showed the inverse time behaviour. According to these results, the cold hardening-induced endodormancy, high frost resistance and accumulation of saccharides and proline are the important prerequisites for the successful cryopreservation of shoot tips of in vitro grown apple plants.     

Drivers of stem radial variation and its pattern in peatland Scots pines: A pilot study

Dendrometers are useful tools to analyze intra-annual variation of radial growth in trees, but have rarely been applied in marginal environments. Our aim in this study was to explore stem radial variation (SRV) of Scots pines (Pinus sylvestris L.) growing in a marginal environment on top of a peatland and compare it with stem radial variation of Scots pines growing in a nearby forest. We compared high-resolution (30 min) tree-growth of the peatland and forest pines in two consecutive years in two ways. First, we modeled raw SRV using site and weather parameters as predictors, to determine if and in what way stem radial variation depends on the site type. Second, we split the SRV signal into sub-series of varying length to test for differences between the time-series pattern of peatland and forest SRV with clustering methods and classifier models. We found indications that site type is influencing raw stem radial variation as: 1) an intercept, i.e. forest trees tended to grow more than peatland trees (as expected); 2) an interaction factor with structural and weather parameters, i.e. response of the forest trees to changing environmental parameters was different than the response of the peatland trees. Conversely, with regard to the temporal pattern of the stem radial variation, we found that the conditions within one year, e.g. weather patterns, were more important than site conditions, especially at short time scales. However, with increasing length of the sub-series the relative accuracy of the classifier models increased. Our results indicate that the site type was important for the raw SRV (amplitude) but not for the SRV pattern, which might be important to consider when comparing intra-annual signals from multiple sites.     

The interrelationship of growth and frost tolerance in winter rye

The reduction in growth of winter cereals that occurs in the fall is thought to be required for the development of frost resistance. In the present study, the interrelationship of freezing tolerance and growth was examined by raising winter rye ( Secale cereale cv. Puma) plants at 20/16°C (day/night) and at 5/3°C under 8-, 16- and 24-h daylengths to vary growth rates and frost tolerance. Temperature and irradiance were quantified as thermal time, photothermal time and photosynthetic photon flux and examined by multiple linear regression in order to determine their effects on growth and frost tolerance of rye shoots. At low temperature, both growth and frost tolerance were markedly influenced by daylength and irradiance. Plants grown at 5/3°C with a short daylength accumulated shoot dry weight and increased frost tolerance at a greater rate per unit photothermal time or photon flux than plants grown at longer daylengths. Moreover, 5/3°C plants grown with a 16-h day grew more slowly and were less frost tolerant than plants grown with a 24-h day. We conclude that the interrelationship between growth and frost tolerance is a quantitative one. Frost tolerance is induced only by low temperature, but the development of forst tolerance is dependent upon both irradiance, which affects the amount of photoassimilate available, and daylength, which may affect the partitioning of photoassimilates between growth and frost tolerance.     

Changes in fatty acid composition of winter wheat during frost hardening

Twelve day old winter wheat seedlings (cvs Kharkov, frost hardy and Champlein, less hardy) accumulated linolenic acid at the expense of linoleic acid during controlled hardening. The change was most pronounced in the roots, where it was not specific to the phospholipid fraction. It was less marked in the leaves, but occurred there mainly in the phospholipids. The lack of differences between fatty acid profiles of the two cultivars rules out the explanation of varietal differences in frost hardiness in winter wheat on the basis of major changes in fatty acid unsaturation.     

A stochastic model of tree architecture and biomass partitioning: application to Mongolian Scots pines

Background and Aims

Mongolian Scots pine (Pinus sylvestris var. mongolica) is one of the principal species used for windbreak and sand stabilization in arid and semi-arid areas in northern China. A model-assisted analysis of its canopy architectural development and functions is valuable for better understanding its behaviour and roles in fragile ecosystems. However, due to the intrinsic complexity and variability of trees, the parametric identification of such models is currently a major obstacle to their evaluation and their validation with respect to real data. The aim of this paper was to present the mathematical framework of a stochastic functional–structural model (GL2) and its parameterization for Mongolian Scots pines, taking into account inter-plant variability in terms of topological development and biomass partitioning.

Methods

In GL2, plant organogenesis is determined by the realization of random variables representing the behaviour of axillary or apical buds. The associated probabilities are calibrated for Mongolian Scots pines using experimental data including means and variances of the numbers of organs per plant in each order-based class. The functional part of the model relies on the principles of source–sink regulation and is parameterized by direct observations of living trees and the inversion method using measured data for organ mass and dimensions.

Key Results

The final calibration accuracy satisfies both organogenetic and morphogenetic processes. Our hypothesis for the number of organs following a binomial distribution is found to be consistent with the real data. Based on the calibrated parameters, stochastic simulations of the growth of Mongolian Scots pines in plantations are generated by the Monte Carlo method, allowing analysis of the inter-individual variability of the number of organs and biomass partitioning. Three-dimensional (3D) architectures of young Mongolian Scots pines were simulated for 4-, 6- and 8-year-old trees.

Conclusions

This work provides a new method for characterizing tree structures and biomass allocation that can be used to build a 3D virtual Mongolian Scots pine forest. The work paves the way for bridging the gap between a single-plant model and a stand model.     

Implications of varying pipe model relationships on Scots Pine growth in different climates

1. The process-based model SIMFORG , based on the pipe theory, was parameterized for Scots Pine at six locations along a north–south gradient in Europe. The ratio of foliage mass to stem cross-sectional area was changed as a function of potential evapotranspiration as proposed by Berninger et al. (1995).
2. Allocation to the stem differed between the locations and affected consequently the stemwood production. Variation in the net primary production and differences in the pipe model parameters were responsible for these differences. There was good agreement between measured and simulated data.
3. Increase in primary production, as predicted by climate-change senarios, increased allocation to the stem. However, the results were sensitive to changes in the foliage mass to stem sapwood cross-sectional area ratio. The changes in allocation were higher in the north than in the south.     

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   

The relation between membrane lipid phase separation and frost tolerance of cereals and other cool climate plant species

Abstract. The temperatures at which liposomes prepared from membrane phospholipids begin to phase separate were compared to the temperatures at which intact plants were damaged. Woody perennials tolerated temperatures below which their membrane phospholipids began to phase separate. By contrast, rye and wheat seedlings were damaged about 25°C above their phase separation temperature. Differences in tolerance among cultivars pre-hardened to frost were reflected by changes of the phase separation temperature. The results support the notion that alterations in membrane lipid composition are associated with frost hardening. A correlation between the temperature of phase separation and frost tolerance suggests that lipid properties may influence freezing tolerance of cereals; however, the lethal event is apparently not phase separation of the membrane phospholipids.     

Interactions between growth,herbivory and long-term foliar dynamics of Scots pine

It is generally thought that carbon-limited conifers with low priority stem growth investment will suffer significantly reduced wood formation following defoliation by insects, as long as resource sinks (apical buds and young needles) are unaffected compared to sources (mature needles). We examined the long-term consequences of periodic defoliation by a moth (Bupalus piniaria L.) on the growth of Scots pine (Pinus sylvestris L.), by retrospectively determining annual rates of needle retention using the needle trace method, and comparing these rates with patterns of radial growth obtained by tree-ring analysis. Cumulative moth densities in the current and previous year had the strongest negative influence on subsequent tree growth. Radial and volume increments were reduced substantially (by up to 50%) for 2-3 years after peaks in the moth population. In turn, tree growth was positively correlated with needle retention, with better growth promoting better retention in the following two seasons. This dominant relationship masked the more subtle impact of B. piniaria on needle retention. However, when each needle cohort was examined separately, it was possible to detect the immediate effects of B. piniaria on the loss of the youngest (0 to 1-year-old) needle cohort. Needle budgeting differed for trees in two study compartments, where the rate of tree growth was evidently different. In the compartment where trees grew more slowly they retained a greater number of needle sets over time by shedding fewer of the older needles, but they responded more quickly to the negative effects of the defoliator by losing needles more rapidly in years when the defoliator was abundant.