Location: Soil Dynamics Research2011 Annual Report
1a. Objectives (from AD-416)
The long-term objectives of this project are to improve understanding of the effects of rising atmospheric carbon dioxide (CO2) concentration on: agricultural productivity; the role of agronomic management in the sequestration of atmospheric CO2 as organic C in soil; and the emission of greenhouse gases (GHG) from agro-ecosystems. Specifically, we will focus on: (1) determining the impacts of elevated atmospheric CO2 and fertilization on plant production, soil C and N dynamics (including C sequestration), soil physicochemical properties, and soil biological properties for adapting Southeastern pasture systems to conditions of changing climate; (2) evaluating the interacting effects of fertilization and elevated atmospheric CO2 on emissions of GHG from soils in Southeastern pasture systems to develop strategies for mitigating the net impact of pasture systems on climate change; and (3) determining the effects of elevated atmospheric CO2 on the establishment and spread of invasive weeds and endemic crop diseases to adapt control strategies to a changing environment.
1b. Approach (from AD-416)
A long-term Southeastern pasture system, using bahiagrass exposed to current and projected levels of atmospheric CO2 and either managed (N added) or unmanaged (no N), is on-going. Carbon flux to plants (biomass growth, allocation, and quality) and soil will be determined with supporting data on soil physicochemical properties. Emphasis will be given to measuring soil C and N dynamics and C storage, root growth, decomposition, water quality, microbial community structure, and GHG (CO2, N2O, and CH4) flux from soil. In addition, container studies examining invasive weeds and endemic plant diseases important to the southeastern U.S will be conducted under the same CO2 levels as the pasture study. Invasive work will occur in two phases: (1) herbicide trials with selected invasive weeds; and (2) herbicide trials with invasives in competition with crop plants. Herbicide efficacy, re-growth, biomass, and tissue quality will be determined at study termination. Disease work will focus on various types of pathogens, i.e., fungal, bacterial, and viral, as well as soil-borne and aerial. Plants will be grown and harvested as for the invasive weed research. Plants will be monitored for symptoms and signs of disease. In all cases, disease incidence (percent plants infected) and severity (proportion of each plant affected) will be assessed. Effects of CO2 on disease development will be assessed by monitoring time to symptom development, latent period (time to sporulation), sporulation (quantity of spores produced), and sporulation period. The effect of CO2 on agronomic systems is a critical, yet neglected, area of research. Integrating data from these studies will aid understanding of the effects of future levels of atmospheric CO2 on agronomic systems in regard to production, the ability to help mitigate global change via sequestration of C in soil, and management of invasive weeds and endemic plant diseases.
3. Progress Report
Global change research at the ARS-USDA National Soil Dynamics Laboratory (NSDL) addresses the impacts of elevated carbon dioxide under differing pasture management practices (nitrogen) on soil carbon storage. Pasture aboveground biomass data have been collected and analyzed; soil cores for root and soil carbon as well as lysimeter solution samples have been collected and are being processed. Our research has begun to address the impacts of elevated carbon dioxide on invasive weeds and plant diseases. Sensitive and resistant lines (to glyphosate) of pigweed were grown under elevated and ambient atmospheric carbon dioxide; data have been collected and are currently being analyzed. A study of the effects of atmospheric carbon dioxide concentration on a plant disease is in preparation. Our research is seeking to understand factors affecting trace gas (carbon dioxide, methane, and nitrous oxide) efflux from agricultural and horticultural systems. Carbon dioxide efflux from both a pasture and an outplanted ornamental horticultural system continues to be monitored (24 hours per day) using Automated Carbon Efflux Systems (ACES). Trace gas emissions are being assessed weekly in both systems. Gas samples are collected in situ using the static closed chamber method according to USDA’s Greenhouse Gas Reduction Through Agricultural Carbon Enhancement network (GRACEnet) protocols and analyzed using gas chromatography. In both studies, soil carbon data are also being collected to determine soil C sequestration potential.
1. Carbon sequestration and greenhouse gas mitigation in ornamental horticulture. Increased atmospheric carbon dioxide (CO2) concentration and other trace gases (i.e., methane and nitrous oxide) are widely believed to be the driving factors behind global warming; however, little work has focused on the contributions from specialty crop industries such as ornamental horticulture. Horticulture has the potential to reduce these emissions while increasing carbon (C) sequestration. A review by ARS scientists at the National Soil Dynamics Laboratory at Auburn, AL, outlines potential areas in ornamental horticulture where practices can be altered to increase C sequestration and mitigate greenhouse gas emissions. This information is critical for fine-tuning Best Management Practices to maximize productivity and profitability while minimizing greenhouse gas (GHG) emissions. In addition, determining C sequestration potential of various landscape species when planted into urban and suburban landscapes could provide homeowners a means of directly contributing to mitigation of climate change.
2. Soil fungi respond more strongly than fine roots to elevated carbon dioxide (CO2). Rising atmospheric CO2 concentration will affect belowground processes and function but the direction and magnitude of change for many soil processes remain unknown. Minirhizotron observations indicated that elevated CO2 increased both fine root and mycorrhizal tip standing crop by more than 50% deeper in the soil, but rhizomorph standing crop was nearly doubled throughout the soil profile. Findings by ARS scientists at the National Soil Dynamics Laboratory at Auburn, AL, suggest that elevated CO2 led to a greater reliance on fungal symbionts, rather than increased root growth, to meet additional nutrient requirements.
3. Characterizing root distribution with adaptive neuro-fuzzy analysis. Root-soil relationships are pivotal to understanding crop growth and function in a changing environment but are difficult to measure and have high variation among samples which often leads to non-significance when standard statistics are employed. An adaptive neuro-fuzzy inference system (ANFIS) was successfully applied to characterize vertical and horizontal root distribution patterns of a potato crop grown under ambient and elevated levels of atmospheric carbon dioxide by ARS scientists at the National Soil Dynamics Laboratory at Auburn, AL. ANFIS offers a viable alternative to more traditional statistical techniques for evaluation of complex root distribution patterns.
Prior, S.A., Runion, G.B., Marble, C., Rogers Jr, H.H., Gilliam, C.H., Torbert III, H.A. 2011. A review of elevated atmospheric CO2 effects on plant growth and water relations: implications for horticulture. HortScience. 46(2):158-162.