Interactive Effects of Elevated Carbon Dioxide and Drought on Wheat

Atmospheric CO 2 concentration ( C a ) continues to rise. An imperative exists, therefore, to elucidate the interactive effects of elevated C a and drought on plant water relations of wheat ( Triticum aestivum L.). A spring wheat (cv. Yecora Rojo) crop was exposed to ambient (Control: 370 μmol mol −1 ) and free‐air CO 2 enrichment (FACE: ambient + 180 μmol mol −1 ) under ample (Wet), and reduced (Dry), water supplies (100 and 50% replacement of evapotranspiration, respectively) over a 2‐yr study. Our objective was to characterize and quantify the responses of 26 edaphic, gas exchange, water relations, carbohydrate pool dynamics, growth, and development parameters to rising C a and drought. Increasing C a minimized the deleterious effects of soil–water depletion by increasing drought avoidance (i.e., lower stomatal conductance and transpiration rate, and growth and development of a more robust root system) and drought tolerance (i.e., enhanced osmoregulation and adaptation of tissue) mechanisms, resulting in a 30% reduction in water stress–induced midafternoon depressions in net assimilation rate. An elevated C a –based increase in daily and seasonal carbon gain resulted in a positive feedback between source capacity (shoots) and sink demand (roots). Devoid of a concomitant rise in global temperature resulting from the rise in C a , improved water relations for a herbaceous, cool‐season, annual, C 3 cereal monocot grass (i.e., wheat) are anticipated in a future high‐CO 2 world. These findings are applicable to other graminaceous species of a similar function‐type as wheat common to temperate zone grassland prairies and savannas, especially under dryland conditions.