LINEAR RELATIONS BETWEEN CARBON-DIOXIDE CONCENTRATION AND RATE - OF DEVELOPMENT TOWARDS FLOWERING IN SORGHUM, COWPEA AND SOYBEAN

Negative linear relations were detected (P < 0.005) between the rate of progress from sowing to panicle initiation and CO2 concentration (210-720 mu mol CO2 mol(-1) air) for two genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relations between CO2 concentration and the rate of progress from sewing to first flowering were also negative in soyabean [Glycine max (L). Merrill] (P < 0.025), but positive in cowpea [Vigna unguiculata (L.) Walp.] (P < 0.025), albeit that in both grain legumes sensitivity was much less than in sorghum. Thus CO2 elevation does not delay flowering in all short-day species. The considerable effect of CO2 concentration on times to panicle initiation resulted in large differences among the sorghum plants at this developmental stage; with increase in CO2 concentration, plants were taller with slightly more leaves and more pronounced apical extension. At the same time after sowing however, sorghum plants were heavier (P < 0.05) at 210 than at 360 mu mol CO2 mol(-1) air. In contrast, relations between the dry masses of the soyabean and cowpea plants and CO2 concentration were positive and curvilinear (P < 0.05). It is suggested that the impact of global environmental change could be severe for sorghum production in the semi-arid tropics.