Submitted to: Soil and Crop Science Society of Florida Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2000
Publication Date: N/A
Interpretive Summary: The Problem. Elevated carbon dioxide (CO2) usually increases plant photosynthesis. However, leaves lose some photosynthetic capacity when grown in elevated CO2 if there is a accompanying decrease of the amount and/or the activity of the "RuBisCO" enzyme. This enzyme binds CO2 for incorporation into plant tissues, so any reduction in amount or activity can decrease photosynthesis. Furthermore, the global warming expected with rising CO2 may further decrease plant photosynthetic capacity. What was accomplished. USDA, ARS scientists and other scientists studied rice at ambient and twice-ambient CO2 concentrations and temperatures of 28, 34, and 40 degrees Celsius (or 82, 93, and 104 degrees Fahrenheit). In high light, the RuBisCO activity was high at all temperatures in ambient CO2 but decreased slightly with increasing temperature in elevated CO2. However, in elevated CO2, the amount of RuBisCO protein was not decreased and photosynthetic rates were higher. How will it help. High CO2 appeared to override any small reduction in activity of RuBisCO in maintaining photosynthesis at elevated CO2 and temperatures. Thus, photosynthesis and vegetative growth (but not seed yield, another story) should be able to continue despite predicted levels of global warming.
Technical Abstract: Elevated carbon dioxide (CO2) increases photosynthesis but plants lose photosynthetic capacity by a drop in amount and activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Our purpose was to determine the effect of elevated temperature and CO2 on rice (Oryza sativa) RuBisCO activity and carbamylation. Rice (cv. IR-30) was grown at temperatures of 40/33, 34/27, and 28/21 Celsius (day/night) and CO2 levels of 330 (ambient) and 660 (elevated) PPM. Leaves were sampled in darkness and light at 23 and 59 days after planting (DAP). In high light at 23 DAP, the carbamylation state, shown by initial RuBisCO activity, was high at all temperatures in ambient CO2 but decreased with increasing temperature in elevated CO2. Variable light at 59 DAP confounded the carbamylation state. Total (Mg2+/CO2-activated) RuBisCO activity at midday was affected little by elevated CO2 at either DAP, indicating that 2-carboxyarabinitol-1-phosphate (CA1P), the RuBisCO inhibitor, was not responsible for changes of initial activity. RuBisCO protein was not affected by elevated CO2. Canopy photosynthesis was greater under elevated CO2. Thus, elevated CO2 appeared to override decreased carbamylation of RuBisCO in maintaining photosynthesis at elevated temperatures.