|Allen, Leon - Hartwell|
Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2000
Publication Date: N/A
Interpretive Summary: The rising global atmospheric carbon dioxide (CO2), currently at 365 parts per million, is expected to double within the next century. Consequently, climatic models predict an increase in air temperature (T) by as much as 4-6C. Present ambient CO2 limits performance of many plants, which therefore sense and respond to increased CO2 through photosynthesis, a process by which leaves absorb CO2 from the air to make components required for plant growth. Although high CO2 is known to enhance soybean growth, there are few studies addressing overall photosynthesis of this important crop to long-term high T and CO2. In this study, by USDA, ARS scientists in Gainesville, FL, soybean was grown season-long under daytime ambient or twice-ambient CO2 and T from 28 to 48C to assess the upper threshold tolerance of leaf photosynthesis with rising air T at high CO2. The results indicate that soybeans grown at twice-ambient CO2 performed well at daytime T as high as 40C, and exceeded their ambient-CO2 counterparts in most aspects of leaf photosynthesis and sugar metabolism. Thus, in the absence of other stresses, soybean should function well photosynthetically under CO2 and temperature conditions predicted for the next century.
Technical Abstract: Soybean (Glycine max L. cv. Bragg) was grown season-long at daytime ambient or twice-ambient [CO2] and temperatures (T) from 28 to 48C. The object was to assess the upper threshold tolerance of photosynthesis and carbohydrate metabolism to rising T at high [CO2], as it is predicted that air T could rise as much as 4-6C within the next century with a doubling of atmospheric [CO2]. Leaf CO2 exchange rate was greater for high-CO2 plants and was highest at 32C, but markedly declined at T above 40C. High-CO2 plants, compared to those at ambient, had greater midday Rubisco, ADPG pyrophosphorylase (ADPG-PPase), SPS and invertase (INV) activities, as well as Chl, soluble protein, starch and sucrose contents. T from 28 to 40C had little effect on midday Rubisco activities, activation and protein, while higher T substantially reduced all three. Predawn Rubisco activity declined with rising T from 28 to 48C, as did the midday Rubisco rbcS transcript level. Activities of ADPG-PPase and SPS and INV paralleled net increases in starch and sucrose, respectively. They were highest at 36- 40C, but declined at higher or lower T. Thus, in the absence of other stresses, soybean photosynthesis should perform well under CO2 and temperature conditions predicted for the next century.