JIA-2018-09

1984 TAO Zhi-qiang et al. Journal of Integrative Agriculture 2018, 17(9): 1979–1990 fertilizer increased NR activity compared to the control (Zn0). Together, zinc fertilizer also caused increases in NR activity under HTS in both cultivars. The activity of NR, measured at D10, was significantly affected by cultivar and zinc fertilizer ( P <0.05). However, the effect of year and the interaction effect of year, cultivar, and zinc fertilizer were not significant. The NR activity of flag leaves, at D22, was significantly affected by cultivar, temperature, zinc fertilizer, cultivar×temperature, cultivar×zinc fertilizer, temperature×zinc fertilizer, and cultivar×temperature×zinc fertilizer ( P <0.01). However, the effect of year and the interaction effect of year, cultivar, temperature, and zinc fertilizer were not significant (Table 1). Zinc fertilizer had the greatest contribution to the total variation of NR activity, followed by temperature, temperature×zinc fertilizer, cultivar, cultivar×temperature×zinc fertilizer, cultivar×zinc fertilizer, and cultivar×temperature (Table 2). Zinc fertilizer had a significant effect on the NR activity of flag leaves under HTS. Compared with the Zn0 treatment under HTS, the reduction in activity of NR was less in both cultivars in both years of Zn15, Zn30, and Zn45 treatments under HTS (Fig. 3). On the 10th d after flowering, NR activity in ZM8 was significantly greater than that in GY2018 ( P <0.05). There was no significant difference in NR activity between the two cultivars at D22 (Fig. 3). Whether at D10 or D22, NR activity of the two cultivars were significantly greater with the addition of any of the three concentrations of Zn fertilizer than compared to no zinc addition ( P <0.05). The greatest difference was observed between Zn15 and Zn0. However, activity rates gradually decreased with the increase of levels of Zn fertilizer ( P <0.05) (Fig. 3). 3.3. Effects of zinc fertilizer and high temperature stress on GS activity The activity of GS was significantly affected by cultivar, zinc fertilizer, and variety×zinc fertilizer at D10 ( P <0.01). At D10, zinc fertilizer significantly increased the GS activities of ZM8 and GY2018 where activity of GS in ZM8 was significantly higher than that in GY2018. GS activity was generally lower with the addition of 0 and 45 mg Zn kg –1 soil than in the other two Zn fertilizer treatments (Fig. 4). The GS activity was significantly affected by cultivar, temperature, zinc fertilizer, and cultivar×temperature at D22 ( P <0.01 or P <0.05) (Table 1). At D22, zinc fertilizer had no effect on GS activity in ZM8 and GY2018; however, the activity of GS in ZM8 was significantly higher than that in GY2018. Heat stress significantly decreased ( P <0.05) the activity of GS in both wheat varieties; there was a greater reduction g a b d g a c ef i bc f h 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 D10-N-Zn0 D10-N-Zn15 D10-N-Zn30 D10-N-Zn45 D22-N-Zn0 D22-N-Zn15 D22-N-Zn30 D22-N-Zn45 D22-H-Zn0 D22-H-Zn15 D22-H-Zn30 D22-H-Zn45 D10-N-Zn0 D10-N-Zn15 D10-N-Zn30 D10-N-Zn45 D22-N-Zn0 D22-N-Zn15 D22-N-Zn30 D22-N-Zn45 D22-H-Zn0 D22-H-Zn15 D22-H-Zn30 D22-H-Zn45 D10-N-Zn0 D10-N-Zn15 D10-N-Zn30 D10-N-Zn45 D22-N-Zn0 D22-N-Zn15 D22-N-Zn30 D22-N-Zn45 D22-H-Zn0 D22-H-Zn15 D22-H-Zn30 D22-H-Zn45 D10-N-Zn0 D10-N-Zn15 D10-N-Zn30 D10-N-Zn45 D22-N-Zn0 D22-N-Zn15 D22-N-Zn30 D22-N-Zn45 D22-H-Zn0 D22-H-Zn15 D22-H-Zn30 D22-H-Zn45 Activity of nitrate reductase (μg g –1 h –1 ) Activity of nitrate reductase (μg g –1 h –1 ) Activity of nitrate reductase (μg g –1 h –1 ) Activity of nitrate reductase (μg g –1 h –1 ) GY2018-2016 g a b de h b c f i c ef g 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ZM8-2016 j b c fg i a b ef j b fde hi 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 GY2018-2017 i b f h g a b de i b cd f 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ZM8-2017 B D A C Fig. 3 Effect of zinc fertilizer, high temperature stress (H), and no-stress (N) on nitrate reductase activity of flag leaves at 10 (D10) and 22 (D22) days after flowering in cultivars, Gaoyou 2018 (GY2018) in 2016 (A) and 2017 (B) and Zhongmai 8 (ZM8) in 2016 (C) and 2017 (D). Zn0–45 mean 0, 15, 30, and 45 mg Zn kg –1 soil, respectively. Bars represent standard deviations (SD). Letters mean significant differences at P <0.05.