INFLUENCE OF DIURNAL DURATION OF CO2 ENRICHMENT AND ROOTING ENVIRONMENT ON SOYBEAN RESPONSE TO ELEVATE CO2

Authors: Heagle, Allen; Booker, Fitzgerald; Miller, Joseph; PURSLEY, W - NCSU CROP SCIENCE DEPT; STEFANSKI, L - NCSU STATISTICS DEPT

Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Carbon dioxide (CO2) concentrations in the atmosphere are increasing because of fossil fuel combustion and deforestation. Most studies indicate that elevated CO2 increases crop yield, and estimates of future world food supply are based partly on such studies. However, controlled experiments to measure effects of CO2 on yield have produced highly variable results, and reasons for this variability are little understood. Differences in methods of plant culture and CO2 enrichment during controlled experiments might be involved. Experiments were conducted with soybean in open-top field chambers near Raleigh, North Carolina to address some of these questions. Effects of 1) rooting environment (plants in pots vs plants in the ground), 2) soil temperature fluctuation (insulated vs non-insulated pots) and 3) daily duration of CO2 enrichment (12 vs 24 hours per day) were studied. Similar physiological, growth and yield responses to CO2 were observed under all of these conditions. Understanding effects of soil nutrition and other environmental factors on plant response to CO2 will show how to maximize food production at CO2 concentrations expected in the future. The present study indicates that relevant knowledge of such effects can be obtained with experiments using large pots in which soil factors can be easily controlled

Technical Abstract: Little is known about effects of diurnal duration of CO2 enrichment and rooting environment on plant response to elevated CO2. Experiments were performed with Essex soybean (Glycine max L. Merr.) at ambient O3 concentrations in open-top field chambers to address each of these questions. In one experiment, plants were grown in 14-liter pots and exposed to double-ambient CO2 for 12 or 24 h d-1 from 5 da after emergence to maturity. Half the pots were insulated to moderate temperatures. Enrichment durations caused similar growth and yield enhancement, and there were no significant CO2 enrichment x insulation interactions. In the second experiment, response to CO2 enrichment was compared for plants grown in the ground or in insulated 14-liter pots. The CO2 concentrations were ambient (366 uLL-1) and approximately 1.3, 1.6, and 1.9 times ambient with CO2 added for 24 h d -1 from 4 da after emergence to maturity. Plants were esampled for net carbon exchange rate (NCER) six times during the season, for weight at 119 DAP and for yield at maturity. Enhancement of NCER by CO2 was not affected consistently by the rooting environment nor was growth. Tests of proportionality of response for yield components showed no evidence of significant differences between plants in pots and in the ground except 100-seed weight. Seed yield enhancement at 1.9 times ambient CO2 was 36% for plants in pots and 33% for plants in the ground