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The physiological ecology of five coastal species has been examined with respect to temperature and its effect on survival and distribution. The aims of the study have been to establish whether any direct correlation exists between distribution and the responses of the plants to temperature at different stages in the life cycle. The species Tinder consideration were the northern Ligusticum scoticum and Mertensia maritima and the southern Crithmum maritimum, Limonium binervosum and Glaucium flavum. Highest germination percentages for each species were found at temperatures close to those associated with the season favourable for germination in the natural habitat. Northern species had higher temperature requirements than the southern, corresponding to spring/ summer and autumn or spring germination respectively. Root respiration, measured as oxygen uptake, was found to be twice as great in the northern Ligusticum and Mertensia as in the southern Crithmum and Limonium over a range of experimental temperatures. This varied to some extent with time and temperature of pretreatment. The single experiment on the southern Glauci.um showed rates similar to those of the northern species. Arrhenius plots' of respiration data for the northern species showed a break in gradient at the upper end of the experimental temperature range which correlated well with apparently limiting July mean temperatures from the distribution maps. The southern Crithmum showed a break at lower temperature range close to the limiting January mean temperature. The response of Limonium to experimental temperature depended on the pretreatment; upper range breaks were shown after low pretreatment temperatures, and lower range breaks after higher pretreatment temperatures. The single experiment on Glaucium gave a straight line Arrhenius plot. Carbohydrate analyses of the same pretreated plants yielded additional information relevant to the survival and thus to the distribution in relation to temperature. The southern Crithmum had the highest starch content at all temperatures while the northern Ligusticum and Mertensia had less. Ratios of soluble sugar to starch were greatest in the northern species, possibly reflecting displacement of the equilibrium from starch to soluble sugar at lower temperatures. Overall a connection has been demonstrated between the direct effects of temperature on the plants and the limitation of distribution by temperature. This is clearest for the two northern species, Ligusticum scoticum and Mertensia maritima, less definite for the southern Crithmum maritimiim, and only suggested for Limonium binervosum with its apparently less simple temperature responses. Glaucium flavum appears anomalous and requires further study.

This thesis investigates physiological mechanisms underlying temperature adaptations in perennial grasses. A comparative approach was employed by using pairs of species that have been collected from lowland sites in thermally contrasting habitats up to 2000 km apart on a north-south direction. The population samples from northern latitudes, i.e. from cooler climates, had higher growth rates at 12°C than southern provenances. Dark respiration rates between 5 and 25°C did not differ between provenances; but acclimatization at 10°C increased the respiration rate in all northern population samples, whereas some southern population samples reduced their respiration rate as a response to acclimatization at 10°C. Northern provenances showed a greater activity of carbohydrate formation in light after periods of 48 hours starvation in darkness. This property could be attributed to the higher activity of RuBP-carboxylase in northern genotypes. No evidence was found that the higher activities are due to higher enzyme concentrations in these genotypes. The enzyme exhibited lower energies of activation in northern provenances in the range 5 - 15°C Activation energies for succinate dehydrogenase in isolated mitochondria were higher for northern population samples in the range 10 - 25°C. Higher specific activities were found for malate dehydrogenase from northern plants between 5 and 25°C. In this temperature range the apparent energies of activation were lower for northern plants. The enzyme displayed positive thermal modulation in both northern and southern provenances. Temperature changes had generally a greater effect on northern provenances. The significance of these findings is discussed in the light of previous reports in the literature and in relation to a possible advantage in the plant's native habitat.

The nature of ice-sheet damage to overwintering forage plants was studied in a controlled environment at non-injurious freezing temperatures. The soil atmosphere was analyzed in a gas-chromatograph and the plants were assessed for injury by histological examination and recovery rates in the greenhouse. Under experimental ice-covers carbon dioxide accumulated in the soil in some instances to as high as 10% while oxygen was depleted to less than 4% of the atmosphere. Plants rooted in such soils were killed after 7 weeks of ice-cover. When the soil under the ice-sheet was flushed with carbon dioxide the plants were killed after periods as short as 21 days. In both cases injury appeared to be physiological rather than mechanical. Furthermore, carbon dioxide accumulation rather than oxygen depletion was responsible for the injury since the plants were able to withstand periods of 3 weeks in a nitrogen-saturated soil. A freeze-thaw-freeze cycle, with moderate freezing temperatures and associated with an ice-sheet, did not appear to be damaging to alfalfa. Continuous ice-covers resulted in a greater accumulation of carbon dioxide and consequently more injury suffered by the plants than where the cover was temporarily broken by a thaw. High soil-moisture conditions which are usually associated with ice-sheets did not result in an increased hydration level in the tissue and consequently did not make the plants more susceptible to cold injury. A technique was developed to determine the ability of plants to withstand ice-encasement. Several varieties and species that were tested exhibited no clear-cut correlation between resistance to ice encasement and frost hardiness. / Land and Food Systems, Faculty of / Graduate

Call number: LD2668 .T4 1963 T65 / Master of Science

Call number: LD2668 .T4 1953 A7 / Master of Science