Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/21/2005
Publication Date: 4/1/2006
Citation: Pritchard, S.G., Prior, S.A., Rogers Jr, H.H., Davis, M.A., Runion, G.B., Popham, T.W. 2006. Effects of elevated atmospheric co2 on root dynamics and productivity of sorghum grown under conventional and conservation agricultural management practices. Agriculture, Ecosystems and Environment. 113:175-183. Interpretive Summary: Root growth of crop plants, almost without exception, is enhanced in CO2-enriched atmospheres. But our understanding of crop root responses to elevated CO2 is far from complete since most information comes from destructive root harvests and often from container grown plants. No data are available concerning the influence of atmospheric CO2 on whole season root growth of any crop grown under different agricultural management practices. Therefore, we evaluated the influence of CO2-enrichment on root growth of a sorghum crop grown with conventional and sustainable management practices. Our data suggest that the stimulation in crop growth anticipated from rising atmospheric CO2 may be diminished by conversion from conventional to more sustainable agricultural systems- at least in the C4 crop sorghum. Current estimates of other crop responses to global environmental change may need modification to take into account interactive effects of agricultural management.
Technical Abstract: The influence of elevated atmospheric CO2 (ambient + 360 mol mol-1) on root dynamics of sorghum (Sorghum bicolor) produced under conventional (tillage following winter fallow) and sustainable (no-till following clover (Trifolium repens) winter cover crop) agricultural management practices was examined. Crops were grown in an outdoor soil bin facility and CO2 treatments were administered using open-top field chambers (OTC). Root dynamics were analyzed using minirhizotrons. In conventional tillage plots, CO2-enrichment increased sorghum seasonal root production and mortality by 58% and 59%, respectively. Root growth, however, was unaffected by [CO2] in sustainable plots. Neither carbon dioxide nor management practices had any impact on the proportion of roots that died by the end of the growing season (i.e., root turnover). The fraction of roots that had died by physiological maturity decreased in a linear fashion from shallow to greater soil depths. Management did not affect cumulative seasonal root production or mortality but did affect vertical root distribution; sustainable management favored shallow root systems whereas conventional management favored deeper rooting. Data emphasize the importance of quantifying production and mortality as separate processes. This study suggests that conversion from conventional to sustainable management practices might negate positive effects of elevated CO2 on root growth, at least in the C4 crop sorghum.