Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2011
Publication Date: 11/1/2011
Citation: Wall, G.W., Garcia, R.L., Wechsung, F., Kimball, B.A., 2011. Elevated atmospheric CO2 and drought effects leaf gas exchange properties of barley. Agriculture Ecosystems and the Environment, 144:390-404. Interpretive Summary: Because atmospheric carbon dioxide concentration is rising, a need exists to predict the effects that global change will have on agricultural crops. Global change may alter precipitation patterns and influence soil moisture available to crops. Because yield potential in the major barley-producing regions of the world is dependent on soil water content, a study was conducted on barley, under open-field conditions to determine how an increase in atmospheric carbon dioxide concentration affects the relationship between assimilation rates and conductance of water vapor and subsequent water use efficiency. Results showed that both well-watered and water-stressed plants grown in elevated atmospheric carbon dioxide concentration had higher assimilation rates and lower conductance resulting in higher water use efficiency. Although the water-stressed plants had less biomass and yield compared to well-watered the advantage due to atmospheric CO2 enrichment for water-stressed plants was greater compared to well-watered. A barley crop growing under higher atmospheric carbon dioxide concentration will have greater yield potential than a crop growing under present-day atmospheric carbon dioxide concentration. Furthermore, high atmospheric carbon dioxide concentration may enhance the survivability and broaden the area where a viable barley crop can be cultivated, particularly in areas where soil moisture availability limits production.
Technical Abstract: Since atmospheric CO2 concentration (Ca) continues to rise, global change seems inevitable. It seems prudent, therefore, to investigate the interactive effects that elevated Ca and drought will impart on the leaf gas exchange properties and subsequent growth response of an important cereal grain crop – barley (Hordeum vulgard L.). A benchmark 2-row German malting barley (cv. Alexa) crop was exposed to ambient (C: Control: 370 'mol mol-1) and free-air CO2 enrichment (F: FACE: ambient +180 'mol mol-1) under ample (W: Wet), and reduced (D: Dry), water supplies (100 and 50% replacement of evapotranspiration, respectively) during the 1994 growing season. Because the uppermost canopy sunlit leaf is more tightly coupled with atmospheric conditions then those lower in the foliage space, our objective was to establish a season-long “carbon footprint” for that leaf [i.e., 650, 730, 905 and 1020 ± 65 g (C) m-2 y-1 for CD, FD, CW, and FW, respectively] – thereby, establishing an upper baseline for the whole-canopy to sequester carbon. Any reduction in potential carbon gain occurred mostly because of nonstomatal limitation under Wet, whereas under Dry stomatal limitations predominated. Furthermore, because elevated Ca reduced gs by 34%, soil-water content was conserved, thereby, enabling stomata to remain open for a longer period into the drought. This resulted in a 28% reduction in water-stress-induced mid-afternoon depressions in net assimilation rate (A) under elevated Ca. Furthermore, on a relative basis the stimulatory effect of elevated Ca was proportionately greater under Dry than Wet. Biotic stresses such as insect herbivore by aphids and insecticide application, somewhat confounded the overall growth response during the latter part of the logistic growth phase. Nevertheless, elevated Ca increased shoot biomass (Bs) by an insignificant 1% during exponential (i.e., early seedling development), but by a significant 11% increase during logistic (i.e., tillering through physiological maturity) growth. Hence, devoid of any concomitant rise in global temperature, improved water relations are anticipated for a herbaceous, cool-season, annual, C3 cereal monocot grass, i.e., barley, in a future high-Ca world. Furthermore, this elevated-Ca-based enhancement appears to be analogous to another graminaceous species such as wheat (Triticum aestivum L. cv. Yecora Rojo) having a similar function-types as barley common to temperate zone grassland prairies and savannas, especially under dryland conditions.