Apical Development and Growth of Barley under Different CO 2 and Nitrogen Regimes

Increases in atmospheric carbon dioxide (CO 2 ) concentration have stimulated interest in the response of agricultural crops to elevated levels of CO 2 . Several studies have addressed the response of C 3 cereals to CO 2 , but the interactive effect of nutrient supply and CO 2 on apical development and spikelet set and survival has not been investigated thoroughly. Hence, an experiment was conducted in the greenhouse to evaluate the effect of high (700 μmol CO 2 mol −1 air) and low (400 μmol mol −1 ) levels of atmospheric CO 2 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 −1–0.11 g N pot −1 week −1 ) and low N (0.3 g N pot −1 ) regimes. The plants were grown in 5 L pots. Development of spike was hastened due to CO 2 enrichment, and the C+ plants pollinated few days earlier than the C— plants. Carbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinated 10 days later and matured 2 weeks later when compared with plants under low N. Carbon dioxide enrichment did not affect the number of spikelets at anthesis. Excess N decreased spikelet abortion and the increased maximum number of spikelets under both [CO 2 ]. Barley plants did not tiller when grown in low [CO 2 ] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appeared 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 of plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9 % under high N regime and by 21 % under low N regime. Under high [CO 2 ] 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. The rate of N application influenced growth and yield components to a greater extent than CO 2 enrichment. At maturity, plant dry matter, kernel weight, the number of kernels per spike, and the number of spikes per plant were higher under high N regime than under low N regime. Long days (16 h), low light intensity (280 μmol m −2 s −1 ), and at constant temperature of 20 °C high [CO 2 ] increased kernel weight and the number of kernels on tiller spikes under high and low N application rate, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.