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Do open‐top chambers overestimate the effects of rising CO 2 on plants? An analysis using spring wheat
Author(s) -
Van Oijen M.,
Schapendonk A. H. C. M.,
Jansen M. J. H.,
Pot C. S.,
Maciorowski R.
Publication year - 1999
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1046/j.1365-2486.1999.00233.x
Subject(s) - photosynthesis , anthesis , microclimate , sugar , horticulture , chemistry , crop , yield (engineering) , zoology , agronomy , botany , biology , materials science , ecology , cultivar , food science , metallurgy
The microclimate in facilities for studying effects of elevated CO 2 on crops differs from ambient conditions. Open‐top chambers (OTCs) increase temperature by 1–3 °C. If temperature and CO 2 interact in their effect on crops, this would limit the value of OTC experiments. Furthermore, interaction of CO 2 and temperature deserves study because increases in atmospheric CO 2 concentration are expected to cause global warming. This paper describes two experiments in which a recently developed cooling system for OTCs was used to analyse the effects of temperature on photosynthesis, growth and yield of spring wheat ( Triticum aestivum L., cv. Minaret). Two levels of CO 2 were used (350 and 700 ppm), and two levels of temperature, with cooled OTCs being 1.6–2.4 °C colder than noncooled OTCs. Photosynthetic rates were increased by elevated CO 2 , but no effect of temperature was found. Cross‐switching CO 2 concentrations as well as determination of A–C i curves showed that plant photosynthetic capacity after anthesis acclimated to elevated CO 2 . The acclimation may be related to the effects of CO 2 on tissue composition: elevated CO 2 decreased leaf nitrogen concentrations and increased sugar content. Calculations of the seasonal mean crop light‐use efficiency (LUE) were consistent with the photosynthesis data in that CO 2 increased LUE by 20% on average whereas temperature had no effect. Both elevating CO 2 and cooling increased grain yield, by an average of 11% and 23%, respectively. CO 2 and temperature stimulated yield via different mechanisms: CO 2 increased photosynthetic rate, but decreased crop light interception capacity (LAI), whereas cooling increased grain yield by increasing LAI and extending the growing season with 10 days. The effects of CO 2 and temperature were not additive: the CO 2 effect was about doubled in the noncooled open‐top chambers. In most cases, effects on yield were mediated through increased grain density rather than increased individual grain weights. The higher growth response to elevated CO 2 in noncooled vs. cooled OTCs shows that a cooling system may remove a bias towards overestimating crop growth response to CO 2 in open‐top chambers.