Elevated CO2 enhanced water use efficiency of wheat to progressive drought stress but not on maize

Abstract

Global rising atmospheric CO₂ concentration ([CO₂]) and drought stress exert profound influences on crop growth and yield. The objective of the present study was to investigate the responses of leaf gas exchange and plant water use efficiency (WUE) of wheat (C3) and maize (C4) plants to progressive drought stress under ambient (a[CO₂], 400 ppm) and elevated (e[CO₂], 800 ppm) atmospheric CO₂ concentrations. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. Under non-drought stress, e[CO₂] increased the net photosynthetic rate (A_n) solely in wheat, and dry matter accumulation (DMA), whereas it decreased stomatal conductance (g _s) and water consumption (WC), resulting in enhanced WUE by 27.82% for maize and 49.86% for wheat. After onset of progressive soil drying, maize plants in e[CO₂] showed lower FTSW thresholds than wheat, at which e.g. g_s (0.31 vs 0.40) and leaf relative water content (0.21 vs 0.43) starts to decrease, indicating e[CO₂] conferred a greater drought resistance in maize. Under the combination of e[CO₂] and drought stress, enhanced WUE was solely found in wheat, which is mainly associated with increased DMA and unaffected WC. These varied responses of leaf gas exchange and WUE between the two species to combined drought and e[CO₂] suggest that specific water management strategies should be developed to optimize crop WUE for different species in a future drier and CO₂-enriched environment.

Keywords: abscisic acid (ABA); climate change; elevated CO2; gas exchange; stomatal conductance.

Figure 1

The average of [CO₂] concentration, temperature (T), and relative humidity (RH) in greenhouse cells designated at 400 and 800 ppm during the experimental period.

Figure 2

Trends of the fraction of transpirable soil water (FTSW) over time for well-watered and drought-stressed pots in which (A) wheat and (B) maize were grown under ambient (400 ppm, a [CO₂]) and elevated (800 ppm, e [CO₂]) atmospheric CO₂ concentrations during progressive soil drying. Error bars indicate the standard error of the means (S.E.) (n = 4).

Figure 3

Changes of net photosynthesis rate (A_n) of (A) wheat and (B) maize plants and stomatal conductance (g_s ) of (C) wheat and (D) maize plants grown under ambient (400 ppm, a[CO₂]) and elevated (800 ppm, e[CO₂]) atmospheric CO₂ concentrations during progressive soil drying. Closed and open circles indicate plants at a[CO₂] and e[CO₂] concentration, respectively. Error bars indicate standard error of the means (SE) (n = 4).

Figure 4

Changes of leaf water potential (ψ_Leaf) of (A) wheat and (B) maize plants, and relative leaf water content (RLWC) of (C) wheat and (D) maize plants grown under ambient (400 ppm, a[CO₂]) and elevated (800 ppm, e[CO₂]) atmospheric CO₂ concentrations during progressive soil drying. Closed and open circles indicate plants at a[CO₂] and e[CO₂] concentration, respectively.

Figure 5

Changes of leaf area (LA) of (A) wheat and (B) maize plants grown under ambient (400 ppm, a[CO₂]) and elevated (800 ppm, e[CO₂]) atmospheric CO₂ concentrations during progressive soil drying. Error bars indicate standard error of the means (SE) (n = 4). The different small letters among treatments in the figure means differences significant at the 0.01 level.

Figure 6

Comparison of water consumption (WC), dry matter accumulation(DMA), and water use efficiency (WUE) of wheat (A, C, E) and maize (B, D, F) plants grown under ambient (400 ppm, a[CO₂]) and elevated (800 ppm, e[CO₂]) atmospheric CO₂ concentrations during progressive soil drying. Error bars indicate standard error of the means (SE) (n = 4). The different small letters among treatments in the figure means differences significant at the 0.01 level.

Figure 7

Changes of leaf ABA concentration of (A) wheat and (B) maize plants under ambient (400 ppm, a[CO₂ ]) and elevated (800 ppm, e[CO₂ ]) atmospheric CO₂ concentrations during progressive soil drying.

Figure 8

Relations between leaf ABA concentration ([ABA]leaf) with stomatal conductance (g_s )of wheat (A) and maize (B) plants grown under ambient (400 ppm) and elevated (800 ppm) atmospheric CO₂ concentrations during progressive soil drying. Error bars indicate standard error of the means (SE) (n = 4).