Effects of CO 2 Enrichment on Biomass Yield and Response to Drought In Radish and Winter Wheat

Alex Hertel* Department of Psychology Department of Environmental Science and Studies 1 Hertel: Effects of CO2 Enrichment on Biomass Yield and Response to Drought In Radish and Winter Wheat Published by Via Sapientiae, 2012 — 97 — issue that arises is how plants will respond to this change, especially those that are cultivated for food. Determining how plants will respond to increased CO2 coupled with changes in water availability is a critical research question. In consideration of the projected rise in atmospheric CO2 and the resulting changes in global water distribution, the experiment was designed to address the question of how drought might affect the growth rate and biomass accumulation of plants subjected to conditions of elevated CO2 and increased drought frequency. One possible response to elevated concentrations of atmospheric CO2 is the “CO2 fertilization effect,” whereby plants undergo more active photosynthesis due to conditions that allow them to increase their intake of CO2. For many plant species, that enrichment of atmospheric CO2 causes a marked increase in growth rate and biomass accumulation (Usuda, 2006; Huang et al., 2007). Evidence also suggests that elevated levels of atmospheric CO2 may increase a plant’s water-use efficiency by reducing the rate of stomatal conductance, which indirectly limits water loss (Huang et al., 2007; Leakey et al., 2009; Morison, 1985). This begs the question of whether conditions of high levels of CO2, which have been documented to close stomata, might also provide better water use efficiency (WUE) due to fewer ports through which water can escape. The objective of this study was to test how radish, Raphanus sativus, and winter wheat, Triticum hybernum, growing in an enriched CO2 environment, will respond under conditions of prolonged drought. The hypothesis was that the plants grown under elevated CO¬2 levels would undergo the CO2 fertilization effect; whereas the plants in the control group growing under ambient conditions would not. It was also hypothesized that additional biomass reserves would make plants grown under elevated CO2 better equipped to deal with drought, as evidenced by a larger biomass yield at the end of the experimental period (Usuda & Shimogawara, 1998). MATERIALS AND METHODS PLANTS AND EXPERIMENTAL CONDITIONS Seeds of radish and winter wheat were planted and grown in Conviron growth chambers at DePaul University. Light was provided by a combination of incandescent and fluorescent bulbs, and each chamber was set for a photon irradiance (light intensity) of 600 μmol m-2 s-1 for a daily light cycle of 18 hours of light/6 hours of darkness. Both chambers were programmed to maintain a constant temperature of 25°C at approximately 60% relative humidity. For the control and experimental treatments, two different concentrations of atmospheric CO2 were employed. In the control, which will be called the ambient concentration (AC), the growth chamber was set to maintain a CO2 concentration of 400 μmol mol-1, which serves as an analog for the actual current CO2 concentration of approximately 385 μmol mol-1. The other growth chamber used in the experimental treatment conditions, which will be called the elevated concentration (EC), was set for a CO2 concentration of 800 μmol mol-1—double what is present today—to reflect the level of atmospheric CO2 that climatologists expect will exist by the end of the century.