Effects of temperature and elevated CO<inf>2</inf> on shoot and root growth of peanut (Arachis hypogaea L.) grown in controlled environment chambers

Abstract

Continuing increases in atmospheric carbon dioxide concentration, [CO 2], will likely be accompanied by global warming. Thus, it is important to quantify and understand the consequences of elevated [CO 2] and temperature on crop growth and yield to develop suitable varieties and agronomic management practices for future climates. The objective of this study was to investigate the growth and development responses of shoots and roots of peanut (Arachis hypogaea L.) grown under different combinations of atmospheric [CO2] and temperature. The study comprised a long-term experiment, in which plants were grown in growth chambers for 112 days, and a short-term experiment, in which growing plants in rhizotrons for 17 days. In the long-term experiment, peanut cultivar Tainan 9 was grown in 20-L containers fitted with minirhizotron observation tubes at 5 cm soil depth and placed in controlled environment chambers under three levels of [CO2] (400, 600, and 800 μmol mol-1) and two levels of air temperature (25/15°C and 35/25°C day/night temperature). In the short-term experiment, two peanut seedlings were grown in each of 18 acrylic rhizotrons with a 6-mm thick soil layer. Rhizotrons with plants were placed in the same growth chambers as above. At 3- to 4-day intervals, rhizotrons were placed on a flatbed scanner to collect digital images from which root length and number were measured using RMS software. At 25/15°C, plants grown at 600 and 800 μmol mol-1 CO2 had main stems that were 24 and 44% longer than those grown at 400 μmol mol-1, while at 35/25°C the main stem length was similar in all [CO2] levels. At 25/15°C, plants showed greater area and dry weight per leaf than at 35/25°C. At harvest, high temperature significantly reduced total leaf area to 574 cm 2 for 35/25°C compared with 921.2 cm2 for 25/15°C. Specific leaf area at low temperature was 22% less than at high temperature. Above ground biomass was increased by elevated CO2 in both temperature treatments. At high temperature, above ground biomass was 56%, 24%, and 16% higher than at low temperature at [CO2] of 400, 600 and 800 μmol mol-1, respectively. Pod dry weight increased with increasing [CO2] at 25/15°C, but was not different among [CO2] levels at 35/25°C. At 25/15°C, pod dry weight was 50% higher than at 35/25°C. As the temperature increased from 25/15°C to 35/25°C, pod dry weight was reduced by 40% at 400, 53% at 600, and 54% at 800 μmol mol-1 CO2. High temperature produced more root length in the containers, whereas low temperature did in the rhizotrons. There were significant interactions between temperature and [CO2] for their effects on main stem length and above ground biomass. High temperature enhanced growth of shoots and roots, but decreased pod dry weight. There was no interaction of elevated [CO2] with higher temperature on the reproductive growth, despite a tendency for beneficial temperature by [CO 2] interaction on vegetative growth and total shoot dry weight. The beneficial effects of increased [CO2] on photosynthesis and growth were overwhelmed by the negative effect of high temperature on reproductive growth.