Effect of In-Field Temperature Modulation on Soybean.

Plant responses to increasing temperature are of great interest as global temperatures continue to rise and the frequency and severity of heat waves are predicted to increase.  Warming of mean global air temperature is in part caused by more rapid increases in night temperatures than day-time temperatures.  Night temperatures influence plant growth through effects on respiration, transpiration, developmental rate, and leaf area among others.  The influence of increased night temperatures has received relatively little attention.  In particular, a big information gap exists for plant responses to high night temperatures under field conditions.  Translatability of information gained under controlled conditions is often questioned, necessitating field studies to reliably quantify effects of predicted increases in night temperature on crop productivity.  The objectives of the present study were to evaluate and demonstrate the utility of in-field temperature-modulation as a tool for future studies, and to generate baseline data on soybean responses to increased night temperature under field conditions.  To this end, infrared heaters were suspended above the canopy during soybean reproductive growth.  This approach successfully increased average night temperatures by nearly 2°C.  However, the achieved temperature modulation did not significantly influence soybean seed yield, and seed oil and protein concentrations in the first year.  Thus, while data to date reveal the need for optimization of the described infrared heater approach, they also indicate that this methodology holds promise for field-based temperature modulation studies.