Crop responses to carbon dioxide doubling: a literature survey
Agricultural and Forest Meteorology, 38 (1-3):
127--145 (October 1986)DOI: 10.1016/0168-1923(86)90054-7
Abstract
Atmospheric carbon dioxide (CO2) concentration will probably double by the middle of the next century. Since this is widely expected to increase crop yields, the Department of Energy has established a research program to gather data on the effects of CO2 on plants and to develop models that can be used to predict how plants will behave in a future high-CO2 world. This paper identifies strengths and weaknesses in the knowledge base for modelling plant responses to CO2. It is based on an extensive tabulation of published information on responses of ten leading crop species to elevated CO2. The response variables selected for examination were: (a) net carbon exchange rate, (b) net assimilation rate, (c) biomass accumulation, (d) root:shoot ratio, (e) harvest index, (f) conductance, (g) transpiration rate and (h) yield. The results were expressed as a predicted percentage change of the variable in response to a doubled CO2 concentration. In most instances, a linear model was used to fit the response data. Overall, the net CO2 exchange rate of crops increased 52\% on first exposure to a doubled CO2 concentration, but was only 29\% higher after the plants had acclimatized to the new concentration. For net assimilation rate, the increases were smaller, but fell with time in a similar way. The C4 crops responded very much less than C3 crops. The responses of biomass accumulation and yield were similar to that for carbon fixation rate. Yield increased on average 41\% for a doubling of CO2 concentration. The variation in harvest index was small and erratic except for soybean, where it decreased with a doubling of CO2 concentration. Conductance and transpiration were both inversely related to CO2 concentration. Transpiration decreased 23\% on average for a doubling of CO2. Crop responses to CO2 during water stress were variable probably because high CO2 both increased leaf area (which increases water use) and reduced stomatal conductance (which decreases water use). However, low nutrient concentrations limited the responses of most crops to CO2. The absolute increase in photosynthetic rate in response to high CO2 concentration was always greater in high light than in low light, but this was not necessarily true of the relative increase. In all except one study, responses to CO2 were larger at high temperature than at low. Most of these studies were done in high light intensity. In low light intensity, the effect of temperature on the CO2 response was smaller.