The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration

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Abstract
Simulated swards of each of two selection lines of Lolium perenne cv. S23 with ‘fast’ and ‘slow’ rates of ‘mature tissue’ respiration were established in growth rooms at 20/15 °C day/night temperatures and studied over four successive regrowth periods of 46, 30, 26 and 53 days duration. The ‘slow’ line outyielded the ‘fast’, both in harvestable shoot (above a 5 cm cut) and in root and stubble. Its advantage increased over successive regrowth periods to 23 per cent (total biomass). Gas analysis measurements on the entire communities (including roots), during the final regrowth period, showed that the ‘slow’ line had a 22–34 per cent lower rate of dark respiration per unit dry weight. This enabled it to maintain its greater mass of tissue for the same cost in terms of CO2 efflux per unit ground area. Half the extra dry weight produced by the ‘slow’ line, relative to the ‘fast’, could be attributed to its more economic use of carbon. The rest could be traced to a 25 per cent greater tiller number which enabled the ‘slow’ line to expand leaf area faster (though not at a greater rate per tiller), intercept more light and fix more carbon, early in the regrowth period.