Tuesday, November 14, 2006

Effects of Elevated Atmospheric CO2 on Root Dynamics of Sorghum, Clover, and Soybean Grown Under Sustainable and Conventional Agricultural Management Systems.

Seth G. Pritchard1, Stephen Prior2, Hugo Rogers2, Brett Runion2, Greg Baccari1, and Micheal A. Davis3. (1) College of Charleston, Dept of Biology, 58 Coming St, Rm 214, Charleston, SC 29424, (2) USDA-ARS, Nat'l Soil Dynamics Lab, 411 S. Donahue Dr., Auburn, AL 36832, (3) Univ of Southern Mississippi, Dept of Biological Sciences, 118 College Drive #5018, Hattiesburg, MS 39406

The influence of elevated atmospheric CO2 (ambient + 360 μmol mol-1) on root dynamics of sorghum (Sorghum bicolor), crimson clover (Trifolium incarnatum), and soybean (Glycine max) produced under conventional (tillage following winter fallow) and sustainable (no-till following clover 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. Growth in CO2-enriched atmospheres did not affect total seasonal root production or mortality of field grown clover, however. Neither carbon dioxide nor management practices had any impact on the proportion of roots that died by physiological maturity (i.e., root turnover) for sorghum or clover. The fraction of roots that had died by physiological maturity decreased in a linear fashion from shallow to greater soil depths in both crops. Although management did not affect cumulative seasonal root production or mortality it did influence 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.  Results from these crops will be compared to results obtained on a similar study with soybean.