CARBON STORAGE AND CYCLING, SOIL MICROBIOLOGY, AND WATER QUALITY IN CO2-ENRICHED AGRO-ECOSYSTEMS

Authors: Rogers Jr, Hugo; PRITCHARD, SETH - COLLEGE OF CHARLESTON; DAVIS, MICHEAL - UNIV. SOUTH. MISSISSIPPI; Prior, Stephen - Steve; Runion, George; Torbert, Henry - Allen; MITCHELL, ROBERT - JOSEPH JONES ECO. RES.

Submitted to: Department Of Energy Annual Report
Publication Type: Other
Publication Acceptance Date: 2/15/2006
Publication Date: 2/15/2006
Citation: Rogers Jr, H.H., Pritchard, S.G., Davis, M.A., Prior, S.A., Runion, G.B., Torbert III, H.A., Mitchell, R.J. Carbon storage and cycling, soil microbiology, and water quality in co2-enriched agro-ecosystems. Final Techinical Reprt, Terrestrial Carbon Processes (TCP) Program of the Office of Science, Biological and Environmental Research (BER), U. S. Department Of Energy Annual Report, Germantown, MD. 7 p.

Interpretive Summary: The level of CO2 in the atmosphere is increasing primarily due to man-made causes. Because plants take in CO2 for growth, much of the carbon ends up in roots; therefore it is important to understand how the rise in CO2 in the atmosphere will affect plant root production, growth, and death. We used standard methods as well as a device called a minirhizotron, which uses a camera fitted into a clear plastic tube placed in the soil, for looking at root growth in three different plant systems growing under elevated levels of CO2: a middle-aged loblolly pine forest, a very young longleaf pine savannah; and a crop study where plants were grown using standard management practices or newer, no-tillage management. In general, growing plants under higher levels of CO2 caused increases in root production, growth, and death in all three studies. Understanding how plant roots react to higher levels of CO2 will help us understand how much carbon these plants can take out of the atmosphere and store in the ground; storing carbon from the atmosphere in roots and soil will help potentially reduce global warming.

Technical Abstract: Carbon emissions from fossil fuel consumption, cement manufacture, and deforestation are modifying the global C cycle; carbon cycling is being changed as a result of rising atmospheric CO2 concentrations. Because much of the C transferred from atmosphere to soils flows through root systems, understanding root responses to CO2-enrichment at the ecosystem level is critical for understanding the potential of soils to mitigate against climate changes by sequestering atmospheric C. We are currently using minirhizotron technology and standard methods to provide information about how rising global CO2 concentrations will impact fine root dynamics in three CO2-enriched plant systems: a mid-rotation loblolly pine (Pinus taeda L.) forest under free-air CO2 enrichment (FACE); a model, regenerating longleaf pine (Pinus palustris Mill.) savannah using open top chambers (OTC); and an agricultural management (conventional vs. conservation practices) study, also using OTC. While FACE stimulated loblolly pine root production, growth, and mortality, data were not statistically significant due to high variability. In general, results from this study suggest modest, if any, increases in ecosystem-level root productivity; however, minirhizotron examination of roots will continue at this site. In the longleaf pine savannah, elevated CO2 increased root length, production, and mortality, but only at the 10-30 cm depth. At termination of this study, after 3 years exposure to elevated CO2, total belowground biomass was increased by 49% in CO2-enriched plots; this increase was primarily due to increases in longleaf pine growth as the biomass of rattlebox, wiregrass, and butterfly weed combined was 28% lower in elevated, compared to ambient, CO2. Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not compete as well, which could alter community function. In the agricultural management study, CO2-enrichment increased sorghum seasonal root production and mortality only in conventionally managed plots. Conservation management favored shallow root systems whereas conventional management favored deeper rooting. This study suggests that, for sorghum, the general positive effects of elevated CO2 on root growth may be negated by conversion from conventional to conservation management. Data continue to be collected from this study for other row and cover crops. In general, preliminary data from these studies suggest that increases in belowground productivity will be accompanied by greater rates of root turnover leading to C transfer, and potentially storage in both natural and managed plant systems. Furthermore, consistent CO2 by depth interactions suggest that root processes will be differentially impacted at different depths causing shifts in root architectures. Such shifts could result in changing patterns of water and nutrient extraction from soils.