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United States Department of Agriculture

Agricultural Research Service

Title: Carbon Storage and Cycling, Soil Microbiology, and Water Quality in Co2 Enriched Agro-Ecosystems

Authors
item Rogers Jr, Hugo
item Pritchard, Seth
item Prior, Stephen
item Torbert, Henry
item Schlesinger, William - DUKE UNIVERSITY
item Amthor, Jeffrey - OAK RIDGE NATIONAL LAB
item Stott, Diane

Submitted to: Department Of Energy Annual Report
Publication Type: Other
Publication Acceptance Date: September 3, 1998
Publication Date: September 3, 1998
Citation: Rogers, H.H., Prichard, S.G., Prior, S.A., Torbert, H.A., Schlesinger, W.H., Amthor, J.S., and Stott, D.E. 1998. Carbon storage and cycling, soil microbiology, and water quality in CO2-enriched agro-ecosystems. Environmental Sciences Division: Summaries of Research in FY 1997. U.S. Department of Energy.

Interpretive Summary: Work to date has shown that growth in elevated CO2 not only affects crop productivity directly by stimulating C dependent anabolic processes, but will indirectly alter agriculture through secondary effects on soil C and N cycling. Growth in elevated CO2 increased biomass returned to soil and altered residue quality in sorghum and soybean. N level of soybean leaves and stems and sorghum stems was reduced leading to increased C/N ratios and lignin concentrations (sorghum stems and soybean leaves only). Residue decomposition of sorghum and soybean in elevated CO2 was the same or less than ambient CO2, regardless of biomass increase, suggesting residue quality may be of overriding importance in controlling decomposition. Biomass quantity and quality, and resultant decomposition may correlate with amount of C transferred to soil from the atmosphere. Utilizing isotopic C techniques, it was observed for sorghum that the amount of new C entering the soil was greater in elevated CO2. For soybean, new C in organic matter was less in high CO2. Higher incorporation of new C into soil organic matter in sorghum compared to soybean may be explained by lower residue C/N ratios and higher CO2 efflux observed for soils where soybean was grown. Increases in biomass coupled with shifts in residue quality may have contributed to greater retention of N in organic pools under high CO2, resulting in reductions in groundwater nitrate level. Understanding of soil/plant and cycling in these systems is hindered by a lack of data on fundamental processes, including root losses due to mortality, rhizodeposition, and respiration. Root growth and development may prove to be of pivotal significance in C transfer from atmosphere to soil. The project provided some of the first in-depth growth and yield studies of carbon dioxide effects on plants in the field. Recently we have shown that growth in elevated CO2 not only increases total biomass returned to soil (roots + aboveground residue), but also alters residue quality which will ultimately determine the amount of carbon transferred to the soil from the atmosphere. Extensions of this work have shown improvement of groundwater quality, and shifts in soil microbiology in carbon dioxide-enriched agricultural ecosystems. Furthermore, we have shown that changes in soil characteristics caused by altered above and below-ground plant growth will likely be crop species dependent, and will also depend on residue management practices.

Technical Abstract: Work to date has shown that growth in elevated CO2 not only affects crop productivity directly by stimulating C dependent anabolic processes, but will indirectly alter agriculture through secondary effects on soil C and N cycling. Growth in elevated CO2 increased biomass returned to soil and altered residue quality in sorghum and soybean. N level of soybean leaves and stems and sorghum stems was reduced leading to increased C/N ratios and lignin concentrations (sorghum stems and soybean leaves only). Residue decomposition of sorghum and soybean in elevated CO2 was the same or less than ambient CO2, regardless of biomass increase, suggesting residue quality may be of overriding importance in controlling decomposition. Biomass quantity and quality, and resultant decomposition may correlate with amount of C transferred to soil from the atmosphere. Utilizing isotopic C techniques, it was observed for sorghum that the amount of new C entering the soil was greater in elevated CO2. For soybean, new C in organic matter was less in high CO2. Higher incorporation of new C into soil organic matter in sorghum compared to soybean may be explained by lower residue C/N ratios and higher CO2 efflux observed for soils where soybean was grown. Increases in biomass coupled with shifts in residue quality may have contributed to greater retention of N in organic pools under high CO2, resulting in reductions in groundwater nitrate level. Understanding of soil/plant and cycling in these systems is hindered by a lack of data on fundamental processes, including root losses due to mortality, rhizodeposition, and respiration. Root growth and development may prove to be of pivotal significance in C transfer from atmosphere to soil.

Last Modified: 4/24/2014