Irrigation methods affect wheat flag leaf senescence and chlorophyll fluorescence in the North China Plain

The water resource shortage in North China Plain is an increasing threat to the sustainability of wheat (Triticum aestivum L.) production. A two-year field experiment was conducted to examine the effects of two supplemental irrigation (SI) methods on wheat flag leaf senescence, chlorophyll fluorescence and grain yield. The following field treatments were conducted: no irrigation (W0); SI with 60 mm of water at jointing and anthesis stages (local quota SI, Wck); SI based on the relative soil water content (SWC) of 0–40 cm soil layers with 65% field capacity (FC) at jointing stage and 70% FC at anthesis stage (W1); SI based on SWC of same soil layers with 70% FC at the jointing and anthesis stage (W2); and SI based on the SWC of same soil layers with 75% FC at jointing stage and 70% FC at anthesis stage (W3). Results showed that W0 accelerated flag leaf senescence and had reduced grain yield. Among irrigation treatments, W2 (and W3 in 2013-2014) significantly increased flag leaf water potential from 7 to 28 days after anthesis (DAA) compared with Wck and W1. Superoxide dismutase activity, catalase activity of W2 increased by 15.41% and 14.96% compared with those in Wck, resulting in the significantly decreased concentration of malondialdehyde and increased concentration of soluble protein at 14–28 DAA. The Fv/Fm at 21–28 DAA and the ΦPSII, qP and NPQ at 14–28 DAA for W2 (and W3 in 2013–2014) were also significantly higher than those of Wck and W1. Eventually, grain yield, water use efficiency and irrigation benefit of W2 were 8704.54 kg ha-1, 20.86 kg ha-1 mm-1 and 31.44 kg ha-1 mm-1, respectively, which were the highest among those of all the treatments. These values increased by 5.82%, 9.65% and 6.00%, respectively, relative to those of Wck. In conclusion, the SI based on 0–40 cm soil layer and use of an appropriate relative SWC (both 70% FC at the jointing and anthesis stages) can reduce irrigation amount, delay leaf senescence and improve grain yield and water use efficiency.