APICAL DEVELOPMENT AND GROWTH OF BARLEY UNDER DIFFERENT CO2 AND NITROGEN REGIMES

Increases in atmospheric carbon dioxide (CO2) concentration have stimu lated interest in the response of agricultural crops to elevated level s of CO2. Several studies have addressed the response of C3 cereals to CO2, but the interactive effect of nutrient supply and CO2 on apical development and spikelet set and survival has not been investigated th oroughly. Hence, an experiment was conducted in the greenhouse to eval uate the effect of high (700 mumol CO2mol-1 air) and low (400 mumol mo l-1) levels of atmospheric CO2 on apical development, spikelet set and abortion, and pre- and post-anthesis growth in spring barley (Hordeum vulgare L.) grown under high N (0.3 g N pot-1 before sowing +0.11 g N pot-1 week-1) and low N (0.3 g N pot-1) regimes. The plants were grow n in 5 L pots. Development of spike was hastened due to CO2 enrichment , and the C+ plants pollinated few days earlier than the C- plants. Ca rbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinat ed 10 days later and matured 2 weeks later when compared with plants u nder low N. Carbon dioxide enrichment did not affect the number of spi kelets at anthesis. Excess N decreased spikelet abortion and the incre ased maximum number of spikelets under both [CO2]. Barley plants did n ot tiller when grown in low [CO2] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appe ared in other treatments, may have contributed to this. Carbon dioxide enrichment increased the C concentration of plants, but decreased the N concentration under high N regime. Both the C and N concentration o f plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9% under high N re gime and by 21% under low N regime. Under high [CO2] increased kernel number on tiller spikes, and increased kernel weight both on main stem and on tiller spikes resulted in a 23% increase in kernel yield under low N regime and 76% increase in kernel yield under high N regime. Th e rate of N application influenced growth and yield components to a gr eater extent than CO2 enrichment. At maturity, plant dry matter, kerne l weight, the number of kernels per spike, and the number of spikes pe r plant were higher under high N regime than under low N regime. Long days (16 h), low light intensity (280 mumol m-2s-1), and at constant t emperature of 20-degrees-C high [CO2] increased kernel weight and the number of kernels on tiller spikes under high and low N application ra te, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.