Effects of Full-Season Temperature Free-Air-Controlled Enhancement (T-FACE) Ecosystem Warming On Leaf Number of Spring Wheat.

Global warming is likely to affect crop canopy development. However, our ability to quantitatively predict how temperature affects processes such as leaf appearance rates still requires refinement. Although controlled-environment chambers can be used to study temperature responses, they introduce numerous biases relative to field studies. Infrared heating can warm field plots with minimal disturbance to wind patterns and other microclimatic factors. We compared effects of canopy temperature on leaf appearance in spring wheat (Triticum aestivum L. cv. Yecora Rojo) using infrared heaters and planting dates to provide different temperature regimes at Maricopa, AZ. A primary objective was to determine whether the T-FACE system resulted in temperature responses that were quantitatively similar to those from natural variation obtained through the planting dates. The T-FACE apparatus provided full-season warming of the canopy by 1.5 and 3.0 ºC during the diurnal and nocturnal periods, respectively. Heated plots in six plantings from 2007 to 2009 and eight additional planting date treatments provided a very wide range of artificial and natural temperature variation. Plots were evaluated twice weekly for leaf number. Leaf number was also simulated using the CSM-Cropsim-CERES-Wheat model. Besides the direct effect of temperature on leaf appearance rate, vernalization and photoperiod affected final leaf numbers via timing of panicle initiation. In comparisons of field observations to simulations, results from T-FACE and planting dates were similar, indicating that the temperature regime of T-FACE was comparable to that from planting-date studies, thus confirming the utility of T-FACE for studying temperature effects at field scales.