The Effect of Extreme High Temperatures On Maize Growth and Development.

Climate change is often associated with global warming and thus the potential impact of temperature rise on crop production. However, many of the projected temperature changes are beyond current weather conditions. This results in a dilemma with respect to designing experimental research for high temperature environments. Experiments are preferably conducted under field conditions, but applying a temperature increase requires sophisticated and expensive equipment, such as those used in the T-FACE experiments. Alternatively experiments can be conducted in greenhouses or gradient tunnels, but in most cases temperature control is somewhat limited. Although growth chamber studies have been criticized for climate change research, they provide unique opportunities for conducting temperature and other environmental response studies in closely controlled and monitored environments. The objective of this study was to determine the impact of high temperature conditions on growth and development of maize. The experiment was conducted in the Georgia Envirotron using five large walk-in growth chambers. The temperature treatments consisted of 45ºC/35ºC, 40ºC/30ºC, 35ºC/25ºC, 30ºC/20ºC and 25ºC/15º using a 12 hour day and night cycle. Light in each chamber was provided by High Pressure sodium and metal halide bulbs, with an average daily total radiation of 32.1 moles m². Seventy 15.12 l containers filled with a South Georgia River sand were placed in each growth chamber. The containers were irrigated three times daily using a drip emitter and fertilizer was applied bi-weekly in the form of Miracle-Gro 24-8-16. Three seeds of the maize hybrid Pioneer 31P42 were planted and thinned to one plant per container after germination at 30ºC/20ºC for one week. Canopy height and vegetative and reproductive development of 10 randomly selected plants per growth chamber were measured daily and growth analysis of four randomly selected plants was conducted weekly. Following sampling the containers were rearranged to their original density. Plants were separated into leaves, stems, roots, and reproductive structures and dried at 70ºC for 72 hours. Prior to drying total root length and leaf area were measured. At approximately two months after sowing the plants became too tall for the growth chambers and the experiment was terminated, allowing for a total of eight growth analysis samplings. Maize did not perform very well in the 45ºC/35ºC environment and all plants died after a few weeks. Average above ground plant biomass at 58 days after planting (DAP) was 68.2 g for the 35ºC/25ºC environment, 59.5 g for the 30ºC/20ºC environment, 53.5 g for the 25ºC/15ºC environment and 17.9 g for the 40ºC/30ºC environment. However, the 25ºC/15ºC plants did not include any reproductive structures at 58 DAP. Total leaf area was highest for the 25ºC/15ºC environment and smallest for the 40ºC/30ºC environment. The results from this study showed that maize growth was highest at a temperature combination of 35ºC/25ºC, but performance dropped quickly as temperatures increased.