We thank Anne Gibson, Katherine Jones, Chris Kolodziejczyk, Alicia Naranjo, Kyle Tiner, and numerous students and temporary technicians for operating the LYCOG facility, conducting sampling, and data processing. L.G.R. acknowledges USDA-NIFA (2010-65615-20632).

1. Collect Soil Monoliths to be used as Weighing Lysimeters
<ol>
	<li>Construct open-ended steel boxes 1 x 1 m square by 1.5 m deep from 8 mm thick steel.</li>
	<li>Press the open-ended boxes vertically into the soil, using hydraulic presses mounted on helical anchors drilled 3 m deep into the soil.</li>
	<li>Excavate the encased monolith using a backhoe or similar equipment.</li>
	<li>Place a fiberglass wick in contact with soil at the base of the monolith. Pass the wick through the steel base into a 10 L reservoir to...

<ol>
	<li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contribution+of+Working+Group+I+to+the+Fifth+Assessment+Report+of+the+Intergovernmental+Panel+on+Climate+Change.">Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.</a> Climate Change 2013: The Physical Science Basis. , 1535 (2013).</li><li>Gerhart, L. M., Ward, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+responses+to+low+CO2+of+the+past.">Plant responses to low CO2 of the past.</a> New Phytol. 188 (3), 674-695 (2010).</li><li>Kimball, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cost+comparisons+among+free-air+CO2+enrichment,+open-top+chamber,+and+sunlit+controlled-environment+chamber+methods+of+CO2+exposure.">Cost comparisons among free-air CO2 enrichment, open-top chamber, and sunlit controlled-environment chamber methods of CO2 exposure.</a> Crit. Rev. Plant Sci. 11 (2-3), 265-270 (1992).</li><li>Hendrey, G. R., Lewin, K. F., Nagy, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Free+Air+Carbon+Dioxide+Enrichment:+DevelopmentProgress,+Results.">Free Air Carbon Dioxide Enrichment: DevelopmentProgress, Results.</a> Vegetatio. 104/105 (1), 16-31 (1993).</li><li>Weng, E., Luo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+hydrological+properties+regulate+grassland+ecosystem+responses+to+multifactor+global+change:+A+modeling+analysis.">Soil hydrological properties regulate grassland ecosystem responses to multifactor global change: A modeling analysis.</a> J. Geophys. Res. 113 (G3), G03003 (2008).</li><li>Brady, N. C., Weil, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Nature and Properties of Soils. , 960 (2002).</li><li>Jenkinson, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+on+the+decomposition+of+plant+material+in+soil.+V.+The+effects+of+plant+cover+and+soil+type+opn+the+logg+of+carbon+from+14C+labelled+ryegrass+decomposing+under+field+conditions.">Studies on the decomposition of plant material in soil. V. The effects of plant cover and soil type opn the logg of carbon from 14C labelled ryegrass decomposing under field conditions.</a> J. Soil Sci. 28 (3), 424-434 (1977).</li><li>Hassink, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preservation+of+plant+residues+in+soils+differing+in+unsaturated+protective+capacity.">Preservation of plant residues in soils differing in unsaturated protective capacity.</a> Soil Sci. Soc. Am. J. 60 (2), 487-491 (1996).</li><li>Oades, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+retention+of+organic+matter+in+soils.">The retention of organic matter in soils.</a> Biogeochemistry. 5 (1), 35-70 (1988).</li><li>Knapp, A. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Consequences+of+more+extreme+precipitation+regimes+for+terrestrial+ecosystems.">Consequences of more extreme precipitation regimes for terrestrial ecosystems.</a> BioScience. 58 (9), 811-821 (2008).</li><li>Ainsworth, E. A., Long, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+have+we+learned+from+15+years+of+free-air+CO2+enrichment+(FACE)?+A+meta-analytic+review+of+the+responses+of+photosynthesis,+canopy+properties+and+plant+production+to+rising+CO2.">What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2.</a> New Phytol. 165 (2), 351-372 (2005).</li><li>Rogers, A., Ainsworth, E. A., Kammann, C. F. A. C. E., Nosberger, J., Long, S. P., Norby, R. J., Stitt, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ch+24:+Value:+Perspectives+on+the+Future+of+Free-Air+CO2+Enrichment+Studies.">Ch 24: Value: Perspectives on the Future of Free-Air CO2 Enrichment Studies.</a> Managed Ecosystems and CO2: Case Studies, Processes, and Perspectives. Ecological Studies. 187, 431-449 (2006).</li><li>Mayeux, H. S., Johnson, H. B., Polley, H. W., Dumesnil, M. J., Spanel, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+controlled+environment+chamber+for+growing+plants+across+a+subambient+CO2+gradient.">A controlled environment chamber for growing plants across a subambient CO2 gradient.</a> Funct Ecol. 7 (1), 125-133 (1993).</li><li>Polley, H. W., Johnson, H. B., Mayeux, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carbon+dioxide+and+water+fluxes+of+C3+annuals+and+C4+perennials+at+subambient+CO2+concentrations.">Carbon dioxide and water fluxes of C3 annuals and C4 perennials at subambient CO2 concentrations.</a> Funct Ecol. 6 (6), 693-703 (1992).</li><li>Polley, H. W., Johnson, H. B., Mayeux, H. S., Malone, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physiology+and+growth+of+wheat+across+a+subambient+carbon+dioxide+gradient.">Physiology and growth of wheat across a subambient carbon dioxide gradient.</a> Ann. Bot. 71 (4), 347-356 (1993).</li><li>Polley, H. W., Johnson, H. B., Marino, B. D., Mayeux, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increase+in+C3+plant+water-use+efficiency+and+biomass+over+glacial+to+present+CO2+concentrations.">Increase in C3 plant water-use efficiency and biomass over glacial to present CO2 concentrations.</a> Nature. 361 (6407), 61-64 (1993).</li><li>Polley, H. W., Johnson, H. B., Mayeux, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increasing+CO2:+comparative+responses+of+the+C4+grass+Schizachyrium.+and+grassland+invader+Prosopis.">Increasing CO2: comparative responses of the C4 grass Schizachyrium. and grassland invader Prosopis.</a> Ecology. 75 (4), 976-988 (1994).</li><li>Polley, H. W., Johnson, H. B., Mayeux, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitrogen+and+water+requirements+of+C3+plants+grown+at+glacial+to+present+carbon+dioxide+concentrations.">Nitrogen and water requirements of C3 plants grown at glacial to present carbon dioxide concentrations.</a> Funct. Ecol. 9 (1), 86-96 (1995).</li><li>Polley, H. W., Johnson, H. B., Mayeux, H. S., Brown, D. A., White, J. W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leaf+and+plant+water+use+efficiency+of+C4+species+grown+at+glacial+to+elevated+CO2+concentrations.">Leaf and plant water use efficiency of C4 species grown at glacial to elevated CO2 concentrations.</a> Int. J. Plant Sci. 157 (2), 164-170 (2012).</li><li>Polley, H. W., Johnson, H. B., Derner, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increasing+CO2+from+subambient+to+superambient+concentrations+alters+species+composition+and+increases+above-ground+biomass+in+a+C3/C4+grassland.">Increasing CO2 from subambient to superambient concentrations alters species composition and increases above-ground biomass in a C3/C4 grassland.</a> New Phytol. 160 (2), 319-327 (2003).</li><li>Johnson, H. B., Polley, H. W., Whitis, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elongated+chambers+for+field+studies+across+atmospheric+CO2+gradients.">Elongated chambers for field studies across atmospheric CO2 gradients.</a> Funct. Ecol. 14 (3), 388-396 (2000).</li><li>Gill, R. 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The LYCOG facility achieves its operational goal of maintaining a 250 to 500 &#181;l L-1 continuous gradient of CA concentrations on experimental grassland communities established on three soil types. The change in CA is linear over the prescribed range. Air temperature increased within each section, but was reset by the between-section cooling coils in most sections. As a result, the operational goal of maintaining a consistent mean temperature from section to section was met over most o...

Atmospheric carbon dioxide concentration (CA) has recently increased past 400 &#181;l L-1 from approximately 270 &#181;l L-1 prior to the Industrial Revolution. CA is forecast to reach at least 550 &#181;l L-1 by 21001. This rate of increase surpasses any CA changes observed over the last 500,000 years. The unprecedented rate of change in CA raises the possibility of non-linear or threshold responses of ecosystems to increasing CA. Most ecosystem-scale CA enrichment experiments apply only two treatments, a single level of enriched CA and a control. These experiments have greatly expanded our understanding of the ecosystem impacts of CA enrichment. However, an alternate approach that can reveal the presence of non-linear ecosystem responses to increasing CA is to study ecosystems across a continuous range of subambient to superambient CA. Subambient CA is difficult to maintain in the field, and has most often been studied using growth chambers2. Superambient CA has been studied using growth chambers, open-top chambers, and free-air enrichment techniques3, 4.
CA enrichment occurs across landscapes containing many soil types. Soils properties can strongly affect ecosystem responses to CA enrichment. For example, soil texture determines the retention of water and nutrients in the soil profile5, their availability to plants6, and the amount and quality of organic matter7-9. The availability of soil moisture is a crucial mediator of ecosystem responses to CA enrichment in water limited systems, including most grasslands10. Past field CA enrichment experiments have typically examined only one soil type, and controlled tests of continuously varying CA enrichment over several soil types are lacking. If effects of CA enrichment on ecosystem processes differ with soil type, there is strong reason to expect spatial variation in ecosystem responses to CA enrichment and ensuing changes in climate11, 12.
The Lysimeter Carbon Dioxide Gradient (LYCOG) facility was designed to address questions of spatial variation in non-linear and threshold responses of ecosystems to CA levels ranging from ~ 250 to 500 &#181;l L-1. LYCOG creates the prescribed gradient of CA on perennial grassland plant communities growing on soils representing the broad range of texture, N and C contents, and hydrologic properties of grasslands in the southern portion of the U.S. Central Plains. Specific soils series used in the facility are Houston Black clay (32 monoliths), a Vertisol (Udic Haplustert) typical of lowlands; Austin (32 monoliths), a high carbonate, silty clay Mollisol (Udorthentic Haplustol) typical of uplands; and Bastsil (16 monoliths), an alluvial sandy loam Alfisol (Udic Paleustalf).
The operational principle employed in LYCOG is to harness the photosynthetic capacity of plants to deplete CA from parcels of air moved directionally through the enclosed chambers. The treatment objective is to maintain a constant linear daytime gradient in CA from 500 to 250 &#181;l L-1. To accomplish this, LYCOG consists of two linear chambers, a superambient chamber maintaining the portion of the gradient from 500 to 390 (ambient) &#181;l L-1 CA, and a subambient chamber maintaining the 390 to 250 &#181;l L-1 portion of the gradient. The two chambers are located side by side, oriented on a north-south axis. The CA gradient is maintained during the portion of the year when vegetation photosynthetic capacity is adequate; typically from late April to early November.
The chambers contain sensors and instrumentation needed to regulate the CA gradient, control air temperature (TA) near ambient values, and apply uniform precipitation amounts to all soils. Soils are intact monoliths collected from nearby Blackland prairie installed in hydrologically-isolated weighing lysimeters instrumented to determine all components of the water budget. Water is applied in events of volume and timing that approximate the seasonality of rain events and amounts during an average precipitation year. Thus, LYCOG is capable of evaluating the long-term effects of subambient to superambient CA and soil type on grassland ecosystem function including water and carbon budgets.
LYCOG is the third generation of CA gradient experiments conducted by USDA ARS Grassland Soil and Water Research Laboratory. The first generation was a prototype subambient to ambient gradient that established the viability of the gradient approach13 and advanced our understanding of leaf-level physiological responses of plants to subambient variation in CA14-20. The second generation was a field-scale application of the concept to perennial C4 grassland, with the gradient extended to 200 to 550 &#181;L L-1 21. This field-scale experiment provided the first evidence that grassland productivity increases with CA enrichment may saturate near current ambient concentrations20, in part because nitrogen availability may limit plant productivity at superambient CA22. LYCOG extends this second generation experiment by incorporating replicated soils of varying texture, allowing robust testing for interactive effects of soils on the CA response of grassland communities.

<table>
	<tbody>
		<tr>
			<td>Dataloggers, multiplexers</td>
			<td>Campell Scientific, Logan, UT, USA</td>
			<td>CR-7, CR-10, CR-21X, SDM-A04, SDM-CD16AC, AM25T</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermocouples: Copper-constantan</td>
			<td>Omega Engineering, Inc., Stamford, CT, USA</td>
			<td>TT-T-40-SLE, TT-T-24-SLE</td>
			<td></td>
		</tr>
		<tr>
			<td>Quantum sensor</td>
			<td>Li-Cor Biosciences, Lincoln, NE, USA</td>
			<td>LI-190SB</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2/H2O analyzer</td>
			<td>Li-Cor Biosciences, Lincoln, NE, USA</td>
			<td>LI-7000</td>
			<td></td>
		</tr>
		<tr>
			<td>Lysimeter scales</td>
			<td>Avery Weigh-Tronix, Houston, TX, USA</td>
			<td>DSL-3636-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Air sampling pump</td>
			<td>Grace Air Components, Houston, TX, USA</td>
			<td>VP 0660</td>
			<td></td>
		</tr>
		<tr>
			<td>Dew-point generator</td>
			<td>Li-Cor Biosciences, Lincoln, NE, USA</td>
			<td>LI-610</td>
			<td></td>
		</tr>
		<tr>
			<td>Cold water chiller</td>
			<td>AEC Application Engineering, Wood Dale, IL, USA</td>
			<td>CCOA-50</td>
			<td></td>
		</tr>
		<tr>
			<td>Chilled water flow control values</td>
			<td>Belimo Air Controls, Danbury, CT, USA</td>
			<td>LRB24-SR</td>
			<td></td>
		</tr>
		<tr>
			<td>Chilled-water cooling coils</td>
			<td>Coil Company, Paoli, PA, USA</td>
			<td>WC12-C14-329-SCA-R</td>
			<td></td>
		</tr>
		<tr>
			<td>Carbon dioxide refrigerated liquid</td>
			<td>Temple Welding Supply, Temple, TX, USA</td>
			<td>UN2187</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylene film</td>
			<td>AT Plastics, Toronto, ON, Canada</td>
			<td>Dura-film Super Dura 4</td>
			<td></td>
		</tr>
		<tr>
			<td>Blower motor/controller</td>
			<td>Dayton Electric, Lake Forest, IL, USA</td>
			<td>2M168C/4Z829</td>
			<td></td>
		</tr>
		<tr>
			<td>Solenoids</td>
			<td>Industrial Automation, Cornelius, NC, USA</td>
			<td>U8256B046V-12/DC</td>
			<td></td>
		</tr>
		<tr>
			<td>Leachate collection pump</td>
			<td>Gast Manufacturing, Benton Harbor, MI, USA</td>
			<td>0523-V191Q-G588DX</td>
			<td></td>
		</tr>
	</tbody>
</table>

a co2 concentration gradient facility for testing co2 enrichment and soil effects on grassland ecosystem function

Continuing increases in atmospheric carbon dioxide concentrations (CA) mandate techniques for examining impacts on terrestrial ecosystems. Most experiments examine only two or a few levels of CA concentration and a single soil type, but if CA can be varied as a gradient from subambient to superambient concentrations on multiple soils, we can discern whether past ecosystem responses may continue linearly in the future and whether responses may vary across the landscape. The Lysimeter Carbon Dioxide Gradient Facility applies a 250 to 500 &#181;l L-1 CA gradient to Blackland prairie plant communities established on lysimeters containing clay, silty clay, and sandy soils. The gradient is created as photosynthesis by vegetation enclosed in in temperature-controlled chambers progressively depletes carbon dioxide from air flowing directionally through the chambers. Maintaining proper air flow rate, adequate photosynthetic capacity, and temperature control are critical to overcome the main limitations of the system, which are declining photosynthetic rates and increased water stress during summer. The facility is an economical alternative to other techniques of CA enrichment, successfully discerns the shape of ecosystem responses to subambient to superambient CA enrichment, and can be adapted to test for interactions of carbon dioxide with other greenhouse gases such as methane or ozone.

The superambient and subambient portions of the gradient are maintained in separate chambers (Figure 1). However, over seven years of operation (2007 &#8211; 2013), the chambers maintained a linear gradient in CA concentration from 500 to 250 &#181;l L-1 (Figure 2) with only a small discontinuity in CA between the exit of the enriched chambers (Monolith 40) and the entrance of the subambient portion of the gradient (Monolith 41).
<p class="jove_conten...

Watch this Scientific Journal Video about A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function at JoVE.com

A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function

The Lysimeter Carbon Dioxide Gradient Facility creates a 250 to 500 &#181;l L-1 linear carbon dioxide gradient in temperature-controlled chambers housing grassland plant communities on clay, silty clay, and sandy soil monoliths. The facility is used to determine how past and future carbon dioxide levels affect grassland carbon cycling.

A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function

Continuing increases in atmospheric carbon dioxide concentrations (CA) mandate techniques for examining impacts on terrestrial ecosystems. Most ...

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11.3K visualizações.  Grassland Soil and Water Research Laboratory.  O Lysimeter Dióxido de Carbono Gradiente Facility cria um 250 a 500 mL L -1 gradiente linear de dióxido de carbono em comunidades pastagem câmaras de habitação de plantas com temperatura controlada em argila, argila siltosa, e monólitos de solo arenoso. A facilidade é usada para determinar como os níveis de dióxido de carbono passadas e futuras afetar ciclismo pastagem de carbono. 