Ecosysterm Warming Affects Vertical Distribution of Leaf Gas Exchange Properties and Water Relations of Spring Wheat.

The vertical distribution of gas exchange and water relations responses to full-season in situ infrared (IR) warming were evaluated for hard red spring wheat (Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semiarid desert region of the Southwest USA.  A Temperature Free-Air Controlled Enhancement (T-FACE) apparatus was used to increase wheat canopy temperature using IR heaters in Heated plots above the corresponding temperature in Reference plots with dummy heaters by target set-point differences of 1.5 and 3.0 ^oC during daytime and nighttime, respectively.   Approximately every six weeks during 2007-2009 wheat was sown under two warming treatments (i.e., Heated, Reference) in three replicates on six planting dates during four months (i.e., Jan., Mar., Sept., Dec.). The flag leaf, and those lower in the canopy, had warmer leaf temperature, and slightly higher net assimilation rates in Heated compared with Reference plots.  Stomatal conductance varied between sampling dates and was greater at the top and decreased thereafter to the bottom of the canopy, but it was virtually unaffected by the Heated compared with Reference plots.  A slight decrease in the internal water status of the crop was observed in Heated compared with Reference plots – as evidenced by a decrease in plant water potential.  But, no difference in relative water content between Heated and Reference plots was detected.  Across the vertical profile, the middle leaf in the canopy exhibited the greatest response to IR warming.  Implementation of an IR-warming T-FACE apparatus proved to be an effective methodology to expose a wheat crop to a huge range of natural and artificially imposed temperature regimes.