Improving the effects of drought priming against post-anthesis drought stress in wheat (Triticum aestivum L.) using nitrogen

Abstract

Water and nitrogen (N) deficiencies are the major limitations to crop production, particularly when they occur simultaneously. By supporting metabolism, even when tissue water capacity is lower, nitrogen and priming may reduce drought pressure on plants. Therefore, the current study investigates the impact of nitrogen and priming on wheat to minimize post-anthesis drought stress. Plant morphology, physiology, and biochemical changes were observed before, during, and after stress at the post-anthesis stage. The plants were exposed to three water levels, i.e., well watering (WW), water deficit (WD), and priming at jointing and water deficit (PJWD) at the post-anthesis stage, and two different nitrogen levels, i.e., N180 (N1) and N300 (N2). Nitrogen was applied in three splits, namely, sowing, jointing, and booting stages. The results showed that the photosynthesis of plants with N1 was significantly reduced under drought stress. Moreover, drought stress affected chlorophyll (Chl) fluorescence and water-related parameters (osmotic potential, leaf water potential, and relative water content), grain filling duration (GFD), and grain yield. In contrast, PJWD couple with high nitrogen treatment (N300 kg ha^-1) induced the antioxidant activity of peroxidase (37.5%), superoxide dismutase (29.64%), and catalase (65.66%) in flag leaves, whereas the levels of hydrogen peroxide (H₂O₂) and superoxide anion radical (O₂ ^-) declined by 58.56 and 66.64%, respectively. However, during the drought period, the primed plants under high nitrogen treatment (N300 kg ha^-1) maintained higher Chl content, leaf water potential, and lowered lipid peroxidation (61%) (related to higher activities of ascorbate peroxidase and superoxide dismutase). Plants under high nitrogen treatment (N300 kg ha^-1) showed deferred senescence, improved GFD, and grain yield. Consequently, the research showed that high nitrogen dose (N300 kg ha^-1) played a synergistic role in enhancing the drought tolerance effects of priming under post-anthesis drought stress in wheat.

Keywords: abiotic stress; antioxidant; drought priming; photosynthesis; wheat.

FIGURE 1

Experimental plan for the study: drought priming (P) was applied at jointing (J) by exposing the plants of two wheat cultivars (Yangmai-158 and Yangmai-22) to moderate drought stress at 55–60% field capacity (FC) for 10 days followed by re-watering. Meanwhile, non-priming plants (WW) were subjected to continued watering at 75–80% FC. At the post-anthesis stage, moderate drought stress at 55–60% FC was applied from 7 to 14 days after post-anthesis followed by re-watering. The treatments during post-anthesis drought stress were assigned as PJWD priming at jointing + post-anthesis drought stress, WD no priming at jointing + post-anthesis drought stress, and WW no priming at jointing + no post-anthesis drought stress. After priming at jointing and application of post-anthesis drought stress treatments, the plants were re-watered directly at 75%–80% FC for recuperation.

FIGURE 2

Effects of pre-drought priming on leaf water potential (Ψw), osmatic potential (Ψs), and leaf relative water content (LRWC) in response to post-anthesis drought stress under two nitrogen (N) rates (N1,180 and N2,300) in Yangmai-158 (A,C,E) and Yangmai-22 (B,D,F) wheat cultivars. Treatments: WW (control), no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 DAA. The horizontal axis shows the time course of the sampling: 1 day before drought stress (0DS), 5 days after drought stress (5DS), 5 and 10 days after re-watering (5DRW and 10DRW). Each vertical bar above the mean values indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.

FIGURE 3

Effects of pre-drought priming on net photosynthetic rate (Pn) and stomatal conductance (gs) in response to post-anthesis drought stress under two nitrogen (N) rates (N1,180 and N2, 300) in Yangmai-158 (A,C) and Yangmai-22 (B,D) wheat cultivars. Treatments: WW (control), no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 days after anthesis. The horizontal axis shows the time course of the sampling: 1 day before drought stress (0DS), 5 days after drought stress (5DS), and 5 and 10 days after re-watering (5DRW and 10DRW). Each vertical bar above the mean value indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.

FIGURE 4

Effects of pre-drought priming on the quantum efficiency of the photochemical reaction in PSII (Fv/Fm) and the quantum yield of the PSII electron transport (ΦPSII), in response to post-anthesis drought stress under two nitrogen (N) rates (N1,180 and N2, 300) in Yangmai-158 (A,C) and Yangmai-22 (B,D) wheat cultivars. Treatments: WW (control), no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 days after anthesis. The horizontal axis shows the time course of the sampling: 1 day before drought stress (0DS), 5 days after of drought stress (5DS), and 5 and 10 days after re-watering (5DRW and 10DRW). Each vertical bar above the mean value indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.

FIGURE 5

Effects of pre-drought priming on chlorophyll (SPAD value) and soluble protein content in response to post-anthesis drought stress under two nitrogen (N) rates (N1,180 and N2, 300) in Yangmai-158 (A,C) and Yangmai-22 (B,D) wheat cultivars. Treatments: WW (control), no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 days after anthesis. The horizontal axis shows the time course of the sampling: 1 days before drought stress (0DS), 5 days after drought stress (5DS), and 5 and 10 days after re-watering (5DRW and 10DRW). Each vertical bar above the mean value indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.

FIGURE 6

Effects of pre-drought priming on malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide anion radical (O₂^–) content in response to post-anthesis drought stress under two nitrogen (N) rates (N1, 180 and N2, 300) in Yangmai-158 (A,C,E) and Yangmai-22 (B,D,F) wheat cultivars. Treatments: WW (control), no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 days after anthesis. The horizontal axis shows the time course of the sampling: 1 day before drought stress (0DS), 5 days after drought stress (5DS), and 5 and 10 days after re-watering (5DRW and 10DRW). Each vertical bar above the mean value indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.

FIGURE 7

Effects of pre-drought priming on catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) content in response to post-anthesis drought stress under two nitrogen (N) rates (N1, 180 and N2, 300) in Yangmai-158 (A,C,E) and Yangmai-22 (B,D,F) wheat cultivars. Treatments: WW (control), no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 days after anthesis. The horizontal axis shows the time course of the sampling: 1 day before drought stress (0DS), 5 days after drought stress (5DS), and 5 and 10 days after re-watering (5DRW and 10DRW). Each vertical bar above the mean value indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.

FIGURE 8

Effects of pre-drought priming on flag leaf area and specific leaf weight in response to post-anthesis drought stress under two nitrogen (N) rates (N1, 180 and N2, 300) in Yangmai-158 and Yangmai-22 (A), and Yangmai-158 and Yangmai-22 (B) wheat cultivars. Treatments: WW, (control) no priming at jointing + no post-anthesis drought stress; PJWD, priming at jointing + post-anthesis drought stress; and WD, no priming at jointing + post-anthesis drought stress. Pre-drought priming was completed during the jointing stage, and post-anthesis drought stress was applied from 7 to 14 days after anthesis. Each vertical bar above the mean value indicates the standard error of three replicates (n = 3) by using three-way ANOVA at P < 0.05.