2007 Annual Report 1a.Objectives (from AD-416) Reduce uncertainty regarding: (1) the effects of rising atmospheric carbon dioxide concentration on crop and pasture production; and (2) the role of agronomic ecosystems in the sequestration of atmospheric carbon dioxide as organic carbon in soils, as well as the release of carbon dioxide and other greenhouse gases from soil, as affected by agricultural management practices. Specifically, determine effects of carbon dioxide on belowground processes which affect crop productivity, soil physicochemical/biological properties, carbon/nutrient cycling, and trace gas efflux from soil. 1b.Approach (from AD-416) Two-year rotational cycles of sorghum and soybean will be maintained under two cropping systems: conventional, using tillage without cover crops; and conservation, using no-till with winter cover crops in rotation (wheat, crimson clover, and sunn hemp). Each cropping system will be grown under current and projected levels of atmospheric carbon dioxide. In addition, a Southeastern pasture system study, using bahiagrass exposed to these carbon dioxide levels, has been initiated. Carbon flux to plants (growth, physiology, and yield) and soil will be determined with supporting data on soil physicochemical properties. Emphasis will be given to measuring soil carbon storage, root development patterns, characterizing the rhizosphere, and trace gas efflux from soil. The relationships of nitrogen to carbon dynamics and to water quality will be examined. Root growth, decomposition, and microbial community structure will be quantified in respect to carbon flow. The effects of carbon dioxide on agronomic systems is a critical, yet neglected, area of research. Integrating data from these studies will help provide a mechanistic understanding of the potential of agronomic systems to mitigated global change via sequestration of atmospheric carbon dioxide in soil. 3.Progress Report None. 4.Accomplishments Increasing atmospheric carbon dioxide concentration impacts production agriculture -- Increasing atmospheric carbon dioxide concentration has led to concerns about potential changes to production agriculture as well as agriculture's role in storing this extra carbon. We have completed nine years in a long-term (10 year) study comparing "conventional" tillage (using a grain sorghum and soybean rotation) with winter fallow and a "conservation" system (using the same primary row-crop rotation) with no tillage and winter cover crops (crimson clover, sunn hemp and wheat) on a Decatur silt loam soil within the soil bin facilities of the NSDL, Auburn, AL. The final soybean crop has been recently planted. Crops of sorghum, sunn hemp, and wheat have been harvested; associated data on above- and belowground plant growth and physiology have been collected for analysis. Results suggest that with conservation management in an elevated carbon dioxide environment, greater residue amounts could increase soil carbon storage as well as increase groundcover for increased soil moisture retention and reduced erosion. This accomplishment addresses Global Change National Program (NP204), Component 3: Agriculture Ecosystem Impacts; Cropping Systems. Increasing atmospheric carbon dioxide concentration impacts invasive weeds in the Southeast -- Invasive plants are a major threat to the Earth's biodiversity and are estimated to cost U.S. agricultural and forest producers 34 billion dollars each year. Understanding how increased atmospheric CO2 may alter establishment, spread, and control of invasive weeds will be crucial to future management strategies. We examined the response of numerous invasive plants important to the southeastern U.S. [sicklepod (Cassia obtusifolia L.), Johnsongrass [Sorghum halepense (L.) Pers.), purple (Cyperus rotundus L.) and yellow (C. esculentus L.) nutsedge, tropical spiderwort (Commelina benghalensis L.), cogongrass (Imperata cylindrical (L.) Beauv.), Chinese privet (Ligustrum sinense Lour.), Lantana (Lantana camara L.) and Vinca [Catharanthus roseus (L.) G. Don] to either 375 micromole mol-1 (ambient) or 575 micromole mol-1 (elevated) CO2 in open top field chambers. Invasive plants, in almost all cases, had significantly more biomass when grown under elevated CO2, suggesting that these invasive weeds will present agricultural producers with even greater problems as atmospheric CO2 continues to rise. This accomplishment addresses Global Change National Program (NP204), Component 3: Agriculture Ecosystem Impacts; Pests. Increasing atmospheric carbon dioxide concentration impacts pastures in the Southeast -- The response of bahiagrass to elevated CO2, using open top chambers over a field soil, was initiated in 2005. After a one-year establishment period, half of all ambient and elevated plots received N at 90 kg/ha; the remaining plots received no N fertilization. Biomass production in the first year was unaffected by CO2 treatment. Two harvests conducted after N treatment initiation both showed significant effects of N and CO2 and an interaction wherein elevated CO2 had no effect in the absence of N, but increased biomass (21%) when N was added. Therefore, while pastures might increase productivity in a CO2-enriched environment, they will only do so provided sufficient N is available. This accomplishment addresses Global Change National Program (NP204), Component 3: Agriculture Ecosystem Impacts; Grazing Land. 5.Significant Activities that Support Special Target Populations Global change research at the NSDL will impact producers of agronomic commodities, including small farmers, and will provide information on global change impacts on crops and their implications for future food security. In addition, this research will aid the global population through greater understanding of means to increase carbon storage in soils and, thus, help reduce the rising atmospheric carbon dioxide concentration. We have recently initiated investigations into alternative crops (sweet potato, cassava, and kudzu) which small farmers might be grown for ethanol production. 6.Technology Transfer Number of non-peer reviewed presentations and proceedings 18 Number of newspaper articles and other presentations for non-science audiences 6 Review Publications Ziska, L.H., Runion, G.B. 2007. Future weed, pest and disease problems for plants. Book Chapter. In: Newton, P.C.D., Carran, R.A., Edwards, G.R., Niklaus, P.A., editors. Agroecosystems in a Changing Climate. Boca Raton, FL: CRC Press. p. 261-287.