Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/13/2013
Publication Date: 5/29/2013
Citation: Sicher Jr, R.C. 2013. Combined effects of CO2 enrichment and elevated growth temperatures on metabolites in soybean leaflets; evidence for dynamic changes of TCA cycle intermediates. Planta. 238:369-380. Interpretive Summary: Global temperatures are predicted to increase by five degrees Celsius or more during the current century because of a buildup of heat trapping gasses in the atmosphere. The gas most responsible for increased global temperatures is carbon dioxide, which is an essential molecule for plant growth. Elevated temperatures induce heat stress, decrease plant growth rates, and negatively impact crop yields. Prior research has shown that enriching the air with carbon dioxide reverses the inhibition of plant growth by high temperatures. Using metabolite profiling procedures, we determined which biochemical pathways were altered in soybean leaves by growing plants with above ambient temperatures. Two thirds of the compounds measured in soybean leaves were altered by heat stress and the conversion of sugars to other plant compounds was most susceptible to elevated growth temperatures. Importantly, this was almost completely reversed by increasing carbon dioxide levels in the air. Therefore, atmospheric carbon dioxide levels are a critical factor in plant responses to temperature stress. These findings are of interest to scientists and policy makers interested in the impact of global climate change on agriculture.
Technical Abstract: Soybean (Glycine max [Merr.]L.) was grown in indoor chambers with ambient (38 Pa) and elevated (70 Pa) CO2 and day/night temperature treatments of 28/20, 32/24, and 36/28 °C. Net rates of CO2 assimilation increased with growth temperature and were enhanced an additional 25% on average by CO2 enrichment. Stomatal conductance about doubled from the lowest to highest temperature but this was partially reversed by CO2 enrichment. Metabolites were measured thrice daily and 28 of 43 leaf metabolites were altered by elevated growth temperatures. Polyols, raffinose, and GABA increased and 23 nonstructural carbohydrates, organic acids, and amino acids decreased with elevated temperature. Citrate, aconitate, and 2-oxoglutarate decreased over 90% in the 36 compared to the 28 °C temperature treatment. Temperature dependent changes of sugars and organic acids were almost completely reversed by CO2 enrichment but results for amino acids were variable. The above findings suggested that the TCA cycle was particularly susceptible to heat stress under ambient CO2. Mitigating effects of CO2 enrichment on soybean leaflet metabolites were attributed to CO2 effects on photosynthesis, photorespiration, respiration, and on the anaplerotic pathway.