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

Summary

The Lysimeter Carbon Dioxide Gradient Facility creates a 250 to 500 µl 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.

Abstract

Continuing increases in atmospheric carbon dioxide concentrations (C_A) mandate techniques for examining impacts on terrestrial ecosystems. Most experiments examine only two or a few levels of C_A concentration and a single soil type, but if C_A 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 µl L^-1 C_A 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 C_A enrichment, successfully discerns the shape of ecosystem responses to subambient to superambient C_A enrichment, and can be adapted to test for interactions of carbon dioxide with other greenhouse gases such as methane or ozone.

Introduction

Atmospheric carbon dioxide concentration (C_A) has recently increased past 400 µl L^-1 from approximately 270 µl L^-1 prior to the Industrial Revolution. C_A is forecast to reach at least 550 µl L^-1 by 2100¹. This rate of increase surpasses any C_A changes observed over the last 500,000 years. The unprecedented rate of change in C_A raises the possibility of non-linear or threshold responses of ecosystems to increasing C_A. Most ecosystem-scale C_A enrichment experiments apply only two treatments, a single level of enriched C_A and a control. ....

Protocol

1. Collect Soil Monoliths to be used as Weighing Lysimeters

1. Construct open-ended steel boxes 1 x 1 m square by 1.5 m deep from 8 mm thick steel.
2. Press the open-ended boxes vertically into the soil, using hydraulic presses mounted on helical anchors drilled 3 m deep into the soil.
3. Excavate the encased monolith using a backhoe or similar equipment.
4. 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 drain the monolith, and then weld the steel base onto the bottom of the box.
5. Kill existing vegetation on the monoliths by applying a non-re....

Results

The superambient and subambient portions of the gradient are maintained in separate chambers (Figure 1). However, over seven years of operation (2007 – 2013), the chambers maintained a linear gradient in C_A concentration from 500 to 250 µl L^-1 (Figure 2) with only a small discontinuity in C_A between the exit of the enriched chambers (Monolith 40) and the entrance of the subambient portion of the gradient (Monolith 41).

Air temp.......

Discussion

The LYCOG facility achieves its operational goal of maintaining a 250 to 500 µl L^-1 continuous gradient of C_A concentrations on experimental grassland communities established on three soil types. The change in C_A 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.......

Materials

List of materials used in this article

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