Root Respiration and Temperature Limits to the North-South Distribution of Four Perennial Maritime Plants

Abstract

Summary Two northern coastal plants in the British Isles which do not occur south of the 15°C July isotherm Ligusticum scoticum and Mertensia maritima were compared in their temperature-respiration responses with two southern species. The southern species which do not occur north of the 4 °C January isotherm were Crithmum maritimum and Limonium binervosum. The over-wintering roots of the northern species had higher respiration rates than the southern species at all the temperatures tested (5—30°C). Arrhenius plots of temperature against respiration rate gave straight lines in the range 7—30°C for the southern species but showed consistent breaks in the 18—20°C range for both the northern species. Energy of activation values were therefore always lower above 20°C for the northern species. In spite of this declining response to temperature above 20°C it was estimated that the carbohydrate reserves would be reduced by 50% in the over-wintering roots twice as rapidly in the northern species as in the southern, irrespective of the temperature at which it was measured. This inability to conserve over-wintering carbohydrate supplies at high temperatures is suggested as a possible reason for the geographical limitation in the distribution of these northern species.