Climate and plant distribution at global and local scales

This paper investigates, with predictive models, the utility of ecophysiological responses to climate as predictors of plant distribution. At the global scale responses to extreme minimum temperatures and to the hydrological budget effectively predict the distribution limits of the major vegetation types of the World. A minimum temperature of -15°C, for example, appears critical in controlling the poleward spread of vegetation that is dominated by evergreen broadleaved species; however, the presence or absence of more frost resistant species, such as those that are deciduous broadleaved, is not obviously explained in terms of extremes of climate. In such cases, predicting the competitive relationships between species is necessary and dependent on the climatic sensitivity of population dynamics.We are grateful to Hans de Kroon for discussions on the application of matrices to ecology.     

Cold acclimation and photoinhibition of photosynthesis in Scots pine

Cold acclimation of Scots pine did not affect the susceptibility of photosynthesis to photoinhibition. Cold acclimation did however cause a suppression of the rate of CO₂ uptake, and at given light and temperature conditions a larger fraction of the photosystem II reaction centres were closed in cold-acclimated than in nonacclimated pine. Therefore, when assayed at the level of photosystem II reaction centres, i.e. in relation to the degree of photosystem closure, cold acclimation caused a significant increase in resistance to photoinhibition; at given levels of photosystem II closure the resistance to photoinhibition was higher after cold acclimation. This was particularly evident in measurements at 20° C. The amounts and activities of the majority of analyzed active oxygen scavengers were higher after cold acclimation. We suggest that this increase in protective enzymes and compounds, particularly Superoxide dismutase, ascorbate peroxidase, glutathione reductase and ascorbate of the chloroplasts, enables Scots pine to avoid excessive photoinhibition of photosynthesis despite partial suppression of photosynthesis upon cold acclimation. An increased capacity for light-induced de-epoxidation of violaxanthin to zeaxanthin upon cold acclimation may also be of significance.Abbreviations APX ascorbate peroxidase - DHA dehydroascorbate - DHAR dehydroascorbate reductase - Fm maximal fluorescence when all reaction centres are closed - Fv/Fm maximum photochemical yield of PSII - GR glutathione reductase - GSH reduced glutathione - Je rate of photosynthetic electron transport - MDAR monodehydroascorbate reductase - q_N nonphotochemical quenching of fluorescence - q_P photochemical quenching of fluorescence - SOD superoxide dismutase This work was supported by the Swedish Natural Science Research Council and the National Natural Science Foundation of China.     

Protection of plants from frost using hydrophobic particle film and acrylic polymer

Frost damage to potatoes, grapevine and citrus plants was assessed following treatment with either an acrylic polymer (Antistress?) or with a hydrophobic particle film (CM‐96–018). In large freezing tests, the application of the hydrophobic particle film consistently led to less damage whilst the acrylic polymer led to the same amount or more damage when compared to control plants. Detailed examination of the freezing of leaves of all three species using infrared thermal imaging revealed that the hydrophobic particle film delayed the entry of ice from a frozen water droplet containing ice nucleating active bacteria and in some cases for the complete duration of the frost test. In contrast, the acrylic polymer was only able to influence the time of ice nucleation of the leaves of citrus plants. It was concluded that the hydrophobic particle film shows considerable promise as a frost protectant applied to susceptible crops just prior to a freezing event.     

Frost-weathering on Mars: Experimental evidence for peroxide formation

Summary A laboratory study of the interaction of H₂O frost with samples of the minerals olivine (Mg,Fe)₂SiO₄ and pyroxene (Mg,Fe)SiO₃ at –11°C to –22°C revealed that an acidic oxidant was produced. Exposure of the frost-treated minerals to liquid H₂O produced a sudden drop in pH and resulted in the production of copious O_2(g) (as much as ~ 10²⁰ molecules g^–1). Exposure of frost-treated samples to 5 ml of 0.1M HCOONa solution resulted in the rapid oxidation of up to 43% of the formate to CO_2(g). These reactions were qualitatively similar to the chemical activity observed during the active cycles of the Viking lander Gas Exchange and Labeled Release Biology experiments. Attempts to identify the oxidant by chemical indicators were inconclusive, but they tentatively suggested that chemisorbed hydrogen peroxide may have formed. The formation of chemisorbed peroxide could be explained as a byproduct of the chemical reduction of the mineral. The following model was proposed. H^c was incorporated into the mineral from surface frost. This would have left behind a residual of excess OH^– _(ads) (relative to surface H⁺). Electrons were then stripped from the surface OH^– _(ads) (due to the large repulsive potential between neighboring OH^– _(ads)) and incorporated into the crystal to restore charge balance and produce a chemical reduction of the mineral. The resultant surface hydroxyl radicals could then have combined to form the more stable chemisorbed hydrogen peroxide species. While the chemisorbed peroxide should be relatively stable at low temperatures, it should tend to decay to O_(ads) + H₂O_(g) at higher temperatures with an activation energy of 34 kcal mole^–1. This is consistent with the long-term storage and sterilization behavior of the Viking soil oxidants. It is possible that as little as 0.1–1% frost-weathered material in the Martian soil could have produced the unusual chemical activity that occurred during the Viking Gas Exchange and Labeled Release experiments.This paper contains the material given in invited presentations at the COSPAR Meeting, Innsbruck, Austria, 5–7 June 1978 and at the Second Conference on Simulation of Mars Surface Properties, NASA Ames Research Center, 17–18 August 1978     

The manipulation of polar head group composition of phospholipids in the wheat Miranovskaja 808 affects frost tolerance

Caryopses of the frost-resistant cultivar of the wheat Triticum aestivum L., Miranovskaja 808, were germinated and grown in the presence of various concentrations of choline chloride. Changes in the composition of leaf total phospholipids and leaf total fatty acids at two extreme temperatures (25°C and 2°C) as well as changes in frost resistance were followed. A choline chloride concentration-dependent accumulation of phosphatidyl choline was observed in the leaves. Seedlings grown at 2°C accumulated more phosphatidyl choline at each choline chloride concentration than those grown at 25°C. There was an inverse relationship between the contents of phosphatidyl choline and phosphatidic acid in the leaves. Neither the temperature nor choline chloride seemed to affect fatty-acid composition. Modification of polar-head group composition of phospholipids affected frost tolerance: Seedlings grown in the presence of 15 mM choline chloride at 25°C exhibited a freezing resistance equal to that of hardened controls. The data indicate that the polar-head group composition of membrane phospholipids in plants can be easily manipulated and point to the importance of phosphatidyl choline in cold adaptation processes.     

Carry-over effects of ozone and water stress on leaf phenological characteristics and bud frost hardiness of <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings

We examined the carry-over effects of ozone (O₃) and/or water stress on leaf phenological characteristics and bud frost hardiness of Fagus crenata seedlings. Three-year-old seedlings were exposed to charcoal-filtered air or 60 nl l^–1 O₃, 7 h a day, from May to October 1999 in naturally-lit growth chambers. Half of the seedlings in each gas treatment received 250 ml of water at 3-day intervals (well-watered treatment), while the rest received 175 ml of water at the same intervals (water-stressed treatment). All the seedlings were moved from the growth chambers to an experimental field on October 1999, and grown until April 2000 under field conditions. The exposure to O₃ during the growing season induced early leaf fall and reduction in leaf non-structural carbohydrates concentrations in the early autumn, as well as resulting in late bud break and reduction in the number of leaves per bud in the following spring. However, O₃ did not affect bud frost hardiness in the following winter. On the contrary, water stress did not affect leaf phenological characteristics, leaf and bud non-structural carbohydrates concentrations and bud frost hardiness. There were no significant synergistic or antagonistic effects of O₃ and water stress on leaf phenological characteristics, concentrations of leaf and bud non-structural carbohydrates and bud frost hardiness of the seedlings. These results show that the carry-over effects of O₃ can be found on the phenological characteristics and leaf non-structural carbohydrates concentrations, although there are almost no carry-over effects of water stress on phenological characteristics and winter hardiness of the seedlings.     

A novel gene that is up-regulated during recovery from cold shock in Drosophila melanogaster

Gene expression during recovery at 25°C (rearing temperature) after cold shock (0°C) was studied in Drosophila melanogaster using a subtraction technique. A novel gene (Frost, abbreviated as Fst) was considerably up-regulated during recovery after cold shock. In addition, a prolongation of cold shock was more effective for induction. In contrast to cold shock, Fst gene did not respond to heat shock. This gene is apparently the same as the unidentified gene, CG9434. Fst has high internal repeats not only in nucleotide but also in amino acid sequences. In addition, FST protein has a proline-rich region. The deduced amino acid sequence revealed a modular structure; i.e., a signal peptide in the N-terminal region followed by a long hydrophilic region. Therefore, this protein is likely to be directed into ER and secreted into extracellular space.     

A chamber for the simulation of radiation freezing of plants

Frost injury to plants can occur following episodic radiation frosts. In the UK this is particularly important to spring sown crops such as potatoes. Most laboratory based frost studies simulate freezing using either conductive or convective freezing chambers. Such frost tests do not simulate overnight freezing events adequately. A freezing chamber based on radiative cooling is described which mimics overnight radiative freezing. The chamber is rectangular in design (1 m × lm × 2 m high) with a radiative cooling plate at the top of the chamber cooled to -40°C to -45°C using HFC coolants, which acts as a cold black body. The sides of the chamber are also cooled to variable temperatures down to -5°C in order to prevent the chamber walls radiating to the plant material during testing. Using thermocouples to measure air temperature and plant temperature the chamber has been characterised to simulate the radiative cooling conditions found in the UK during autumn and spring. Exotherm detection upon plant freezing is simplified by virtue of the reduction in temperature fluctuation normally experienced at the plant surface during natural freezing. Radiation frosts and subsequent frost damage to potatoes have been recorded in the temperature range -4°C to –5°C. The equipment is recommended for studies of frost damage to plants normally caused by episodic radiation frost events.     

In vitro-selection of hydroxyproline-resistant cell lines of wheat (Triticum aestivum): accumulation of proline, decrease in osmotic potential, and increase in frost tolerance

Five hundred hydroxyproline-resistant cell lines were selected from cell cultures of wheat ( Triticum aestivum L. cv. Koga II) after plating on 10 to 30 m M hydroxyproline (Hyp) containing solid Gamborg B 5 medium. All selected cell lines from 30 m M Hyp-medium contained increased (up to 17-fold) levels of free proline. Seventy-four cell lines were transferred to Hyp-free medium and subcultivated 25 times, for 12 months altogether, after which 80% still had increased proline levels. Fourteen cell lines with increased proline levels were further investigated in liquid media with regard to their frost tolerance, which was measured by means of electrolyte leakage. Ten of them showed increased fros tolerance, with LT 50 values as low as 2.7°C below that of the wild type (-4.7°C). Besides increased proline levels and increased percentage dry weight, the Hyp-resistant cell lines had lower osmotic potentials. Osmotic potentials correlated better than levels of free proline with the increase in frost tolerance.     

Alleviation of frost damage to pear flowers by application of gibberellin

Adverse effects of gibberellin applications on pear trees after frost such as small fruit size, abnormal fruit shape and poor return bloom are often attributed both to the sole use of GA₃ and its overdose. It is unclear whether protection against spring frosts before flower opening is more efficient when GA is applied directly after frost, i.e. before flower opening, or at full bloom or both. In April 2003, early spring frosts at Klein-Altendorf near Bonn, Germany damaged ca. 88% flowers of the early flowering cv. Alexander Lucas, 64% of cv. Conference and ca. 25% of flowers of the later flowering cv. Comice pears. Hence, the objective of the present work was to investigate the optimum timing of the application of low doses of the combined GA₃ and GA_{4 + 7} to improve parthenocarpic fruit set in pears, while maximising fruit quality and size for trees affected by a severe spring frost before full bloom. Return bloom was also considered and quantified. Frost-affected pear trees were treated with gibberellin GA₃+GA_{4 + 7}, either immediately after the frost, at the white bud stage, or at full bloom or both to improve parthenocarpic set. Early flowering cv. Alexander Lucas pear was most affected by the early spring frost, but lost only 25% of fruitlets at June drop, irrespective of GA treatment. June drop was, however, severe in the two other cultivars least affected by frost, i.e. by 33% in cv. Conference and 55% in cv. Comice. Both initial and final fruit set were significantly increased by a combined application of GA₃+GA_{4 + 7} at full bloom, without affecting return bloom, but June drop was also enhanced by GA application. The largest positive effect of GA application on fruit yield, an additional 2 kg of fruit per tree equivalent to €1200/ha, was apparent with the cv. Alexander Lucas, i.e. the cultivar most affected by frost. There was no loss in fruit quality viz fruit size after any of the GA applications with any of the pear cultivars examined and no increase in abnormally-shaped, elongated fruit.