Sunlit, controlled environment growth chambers are essential for comparing plant responses to past, present, and future climates

Authors: ALLEN, LEON - Retired ARS Employee; BOOTE, KENNETH - University Of Florida; JONES, JAMES - University Of Florida; JONES, PIERCE - University Of Florida; PICKERING, NIGEL - Washington State University; Baker, Jeffrey; VU, JOSEPH - Retired ARS Employee; Gesch, Russell - Russ; Gruters-Thomas, Jean; PRASAD, VARA - Kansas State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2020
Publication Date: 11/3/2020
Citation: Allen, L.H., Boote, K.J., Jones, J.W., Jones, P.H., Pickering, N.B., Baker, J.T., Vu, J.C., Gesch, R.W., Thomas, J.M.G., Prasad, V.P. 2020. Sunlit, controlled-environment chambers are essential for comparing plant responses to various climates. Agronomy Journal. 112(6):4531-4549. https://doi.org/10.1002/agj2.20428.
DOI: https://doi.org/10.1002/agj2.20428

Interpretive Summary: Often Free air CO2 Enrichment (FACE) field exposure systems have been considered by Scientists as the ultimate for studying effects of elevated CO2 on crop plants to the exclusion of other exposure systems. However, a USDA-ARS scientist at the Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL along with coauthors, compared the capability of four systems [outdoor, sunlit, Soil-Plant-Atmosphere-Research (SPAR) chambers, temperature-gradient greenhouses (TGG), open top chambers (OTC)] with FACE systems for conducting CO2 effect studies as well as other environmental effect studies on plants. They found for at least half of the 15 characteristics evaluated that SPAR systems provided information that FACE systems were not capable of providing or were simply superior to FACE. SPAR was particularly superior to FACE for the capability of providing information on (1) plant responses to CO2 concentrations with multiple chambers simultaneously that represent past, present and future atmospheric CO2 concentrations, (2) plant responses to temperatures as well as CO2 concentrations simultaneously, (3) plant daytime photosynthesis and transpiration rates as well as nighttime plant dark respiration rates, and (4) for constructing or testing plant growth model responses to atmospheric environmental variables. The authors also point out that a recent review indicates that wide fluctuations of CO2 in FACE exposure systems appear to limit responses of plant photosynthesis, growth, and yield to about 0.65 of that in constant or steady CO2 of the same mean concentration. In summary, this systematic evaluation can provide future researchers solid information for selecting the experimental system for matching and achieving their research objectives.

Technical Abstract: The unique capabilities of various systems for studying the impacts of rising atmospheric carbon dioxide concentration [CO2] and other environmental factors on growth and yield of plants are presented. These systems include Soil-Plant-Atmosphere Research (SPAR) chambers, Free-Air CO2 Enrichment (FACE) facilities, Temperature-Gradient Greenhouses (TGG), and Open Top Chambers (OTC). SPAR chambers have several advantages compared to FACE and other facilities. These advantages include: (1) constant [CO2] and stabilized setpoints; (2) [CO2] controlled to any range of sub-ambient through supra-ambient levels, providing comparison of plant responses to past and future climates from low [CO2] of ~ 180-200 ppm of the Last Glacial Maximum to current ambient [CO2] of = 400 ppm, and any future elevated [CO2]; (3) precise air and dewpoint temperature setpoints, including emulation of realistic daily cycles; (4) calculation of whole-canopy photosynthesis and transpiration rates at short time intervals; (5) calculation of whole-canopy respiration rates during the night; (6) determination of plant responses to temperature alone or including other factors such as [CO2] and soil water availability; (7) simultaneous comparison of plant responses to varying environments, providing data for plant growth modeling; and (8) low operating expense for [CO2]. SPAR units are better suited than FACE systems for about half of 15 attributes of enrichment systems identified in this paper. Limitations of plant responses due to fluctuating elevated [CO2] and the limited range of elevated [CO2] exist for FACE systems. Therefore, controlled environments should be used for quantifying plant performance to environmental variables and for developing mathematical growth response functions under a wide range of [CO2] and climate conditions.