Elevated CO2 and Crop Chemistry

Posted by: chaamjamal on: May 24, 2018

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1. Before it was expropriated by the global warming/climate change movement, the term “Greenhouse Effect” referred to the effect of elevated carbon dioxide in greenhouses on crop chemistry. We know from greenhouse studies going back to the late 19th century that crop chemistry reflects the balance between soil chemistry, air chemistry, and light intensity. The important features of air chemistry are the availability of carbon dioxide for photosynthesis and of oxygen for plant respiration. The important features of soil chemistry are the availability of water, nitrates, phosphates, and minerals.
2. Climate science is apparently concerned about the effect of elevated atmospheric CO2 on agriculture. Initially it was assessed that the effects of climate change would devastate agriculture but later the concern shifted to the effect of elevated atmospheric CO2 on the nutritional quality of crops. These concerns appear to be disconnected from the extensive literature on elevated CO2 agriculture in greenhouses that have been with us for more than a century.
3. Greenhouse operations include irrigation, air circulation to maintain air quality, heating for temperature control, the introduction of carbon dioxide to maintain elevated carbon dioxide levels of 1000 to 2000 parts per million for photosynthesis enrichment, and the availability of sufficient light for photosynthesis to occur. Photosynthesis enrichment improves crop yield. Corresponding changes to soil chemistry are required to preserve the nutritional quality of the crops.
4. It has been found in numerous greenhouse studies since the 19th century that if elevated carbon dioxide is not matched by corresponding changes to soil chemistry, crop chemistry may shift in the direction of higher starch content and lower nutritional quality. These effects are crop specific and vary greatly among crop types.
5. Proper greenhouse management is responsive to these dynamics and involves the management of light and soil chemistry that is appropriate for any given level of carbon dioxide so that crop nutritional quality is maintained. These relationships are described in some detail in the Stitt&Krapp1999 paper listed below and highlighted in bold.
6. The various works of Bruce Kimball of the US Water Conservation Laboratory (with full text available free from the USDA) are unique in this line of research as they are not greenhouse studies but a survey of a large number of such studies carried out to estimate the impact of climate change on crop yield.
7. His work followed in the heels of the landmark “Climate Sensitivity” presentation made by Jule Charney in 1979 in which he presented the finding from climate model studies that a doubling of atmospheric carbon dioxide will cause mean global temperature to rise by 1.5C to 4.5C. The Charney Climate Sensitivity still serves as the fundamental relationship in climate science for the “greenhouse warming effect” thought to be caused by atmospheric carbon dioxide.
8. Kimball followed the Charney format and presented his finding that  a doubling of atmospheric carbon dioxide will increase crop yields worldwide by about 30% with some differences among crops and for different conditions and latitudes. The relevant citations appear below.
9. Kimball, Bruce A. “Carbon Dioxide and Agricultural Yield: An Assemblage and Analysis of 430 Prior Observations 1.” Agronomy journal 75.5 (1983): 779-788.
10. Kimball, B. A., and S. B. Idso. “Increasing atmospheric CO2: effects on crop yield, water use and climate.” Agricultural water management 7.1-3 (1983): 55-72.
11. Kimball, B. A., et al. “Effects of increasing atmospheric CO2 on vegetation.” CO2 and Biosphere. Springer, Dordrecht, 1993. 65-76.
12. Mauney and Kimball. “Growth and yield of cotton in response to a free-air carbon dioxide enrichment (FACE) environment.” Agricultural and Forest Meteorology 70.1-4 (1994): 49-67.
13. Kimball, Bruce A., et al. “Productivity and water use of wheat under free‐air CO2 enrichment.” Global Change Biology 1.6 (1995): 429-442.
14. Kimball, B. A., K. Kobayashi, and M. Bindi. “Responses of agricultural crops to free-air CO2 enrichment.” Advances in agronomy. Vol. 77. Academic Press, 2002. 293-368.
15. Idso and Kimball. “Effects of atmospheric CO2 enrichment on plant growth: the role of air temperature.” Agriculture, ecosystems & environment 20.1 (1987): 1-10.
16. The findings of a selection of GREENHOUSE STUDIES from Besford 1990 to Galtier 1995 presenting measurements of nutritional loss due to an imbalance in CO2 and soil nutrients are listed below. The greenhouse management implications of these findings are described best in the Stitt and Krapp 1999 paper.
17. RT Besford, et al 1990, Journal of Experimental Botany 41.8: 925-931: Compared with tomato plants grown in normal ambient CO2, the 1000 ppm CO2 grown leaves, when almost fully expanded, contained only half as much RuBPco protein. Note: corresponding soil enrichment was not used.
18. Peter Curtis et al, 1998, Oecologia 113.3: 299-313: Total biomass and net CO2 assimilation increased significantly at about twice ambient CO2, regardless of growth conditions. Low soil nutrient availability reduced the CO2 stimulation of total biomass by half, from +31% under optimal conditions to +16%, while low light increased the difference to +52%.
19. Kramer, Paul J. 1981, BioScience 31.1: 29-33: The long-term response to high CO₂ varies widely among species. Furthermore, the rate of photosynthesis is limited by various internal and environmental factors in addition to the CO₂ conc.
20. Curtis, P. S. 1996, Plant, Cell & Environment 19.2: 127-137: Growth at elevated [CO2] resulted in moderate reductions in gs in unstressed plants, but there was no significant effect of CO2 on gs in stressed plants. Leaf dark respiration (mass or area basis) was reduced strongly by growth at high [CO2] > while leaf N was reduced only when expressed on a mass basis.
21. Shahidul Islam et al, 1996, Scientia Horticulturae 137-149: CO₂ enriched tomatoes had lower amounts of citric, malic and oxalic acids, and higher amounts of ascorbic acid, fructose, glucose and sucrose synthase activity than the control. Elevated CO₂ enhanced fruit growth and colouring during development.
22. Stitt & Krapp 1999: Plant, Cell & Environment 22.6-583-621: Increased rates of growth in elevated [CO₂] will require higher rates of inorganic nitrogen uptake and assimilation. An increased supply of sugars can increase the rates of nitrate and ammonium uptake and assimilation, the synthesis of organic acid acceptors, and the synthesis of amino acids. Interpretation of experiments in elevated [CO₂] requires that the nitrogen status of the plants is monitored.
23. Galtier, Nathalie, et al. 1995, Journal of Experimental Botany 1335-1344:  At elevated CO2, the rate of sucrose synthesis was increased relative to that of starch and sucrose/starch ratios were higher throughout the photoperiod in the leaves of all plants expressing high SPS activity. At high C02 the stimulation of photosynthesis was more pronounced. We conclude that SPS activity is a major point of control of photosynthesis particularly under saturating light and C02.
24. At very high CO2 levels, not only sufficient water and nutrients but also sufficient light must be provided  to the plants. This greenhouse management issue is discussed in an excellent article at the CROP KING site:  LINK:  [CROP KING]

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