Location: Soil Dynamics Research2013 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), Auburn, Alabama, 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. Research has begun to address the impacts of elevated carbon dioxide (CO2) on invasive weeds and plant diseases. A study on the effects of elevated atmospheric CO2 on two non-native ornamental plants, including the potential for these plants to become invasive problem species was completed and published. Sensitive and resistant lines (to glyphosate) of pigweed were grown under elevated and ambient atmospheric carbon dioxide; data were inconclusive and this study may be repeated. A herbicide study with yellow and purple nutsedge grown under ambient and elevated carbon dioxide was completed; data are being analyzed. Studies on the effects of atmospheric carbon dioxide concentration on plant diseases are in preparation. 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 carbon (C) sequestration potential.
1. Herbicide rates for nutsedge control will not be altered under elevated atmospheric carbon dioxide (CO2). Elevated atmospheric CO2 effects on invasive plants: the rising level of CO2 in the atmosphere causes most plants to grow larger; while this increases crop yield, it can also increase problems associated with non-native plants. Both yellow and purple nutsedge grew larger under elevated CO2; however, each was completely killed with a standard rate of herbicide indicating that higher rates should not be necessary for adequate control of these weeds in a future, high CO2 environment; a manuscript is currently underway from this study. This information will make farmers and people involved with invasive plants aware that not all non-native plants will be more difficult or expensive to control as atmospheric CO2 continues to rise.
2. Fertilizer placement may affect trace gas loss in horticultural systems. Agriculture is a large contributor of trace gas emissions and much of the work on reducing greenhouse gas (GHG) emissions has focused on row crops and pastures, as well as forestry and animal production systems; however, little emphasis has been placed on specialty crop industries such as horticulture. Placing fertilizer in a dibble hole beneath the plant reduced carbon dioxide loss in nursery containers while incorporating fertilizer into the growth medium increased nitrous oxide; methane loss was consistently low and had no significant effect on total trace gas loss. These results begin to address uncertainties regarding the environmental impact of the horticulture industry on climate change while providing baseline data of trace gas emissions from container production systems needed to develop future mitigation strategies.
3. Rising atmospheric carbon dioxide (CO2) can alter trace gas emissions patterns in terrestrial ecosystems. The rise in atmospheric CO2 concentration could alter terrestrial ecosystems, which are important sources and sinks of greenhouse gases (GHGs) (nitrous oxide and methane), in ways that either stimulate or decrease the magnitude and duration of global warming. A review of field studies was conducted to assess how nitrous oxide (N2O) and methane (CH4) soil fluxes responded to increased CO2 and air temperature. The responses of these GHGs varied among systems with elevated CO2 often stimulating N2O emissions in fertilized systems and CH4 emissions in wetlands, peatlands, and rice paddy fields. Such effects were stronger in clayey soils than in sandy upland soils. However, effects of elevated temperature on N2O and CH4 emissions were inconsistent. This review provides policy makers with current information suggesting that increasing CO2 may enhance global warming by changes in N2O and CH4 emissions; however, the impacts of elevated temperature are unclear in how they may influence feedbacks (positive or negative) of these GHGs in terrestrial ecosystems.
4. Regional-scale climate models more accurately predict precipitation impacts on ecosystem function and carbon (C) dynamics. Drought is one of the most devastating natural hazards and climate change models predict an increase in drought frequency and intensity for the Southern United States (SUS). Using a standard precipitation index, drought was characterized for this area from 1895–2007. No significant changes in drought intensity and duration were found; however, areas in the SUS with high rainfall events appear to be increasing, which may indicate more flooding. Net primary productivity (NPP) decreased in large areas of the eastern portion of the SUS due to increased drought, while NPP increased in most areas of the western SUS due to increased rainfall. These changes in precipitation induced C sinks in most areas of the western SUS and C sources in most areas of the eastern SUS. Further, changes in precipitation resulted in forest, wetland, and cropland ecosystems being C sources, while shrubland and grassland ecosystems acted as C sinks. This work emphasizes the need for regional-scale models to accurately predict how changes in precipitation can impact ecosystem function and C dynamics.
Dijkstra, F.A., Prior, S.A., Runion, G.B., Torbert III, H.A., Tian, H., Lu, C., Venterea, R.T. 2012. Effects of elevated carbon dioxide and increased temperature on methane and nitrous oxide fluxes: evidence from field experiments. Frontiers in Ecology and the Environment. 10(10):520-527.