Night warming from tillering to jointing increases post-anthesis flag leaf photosynthetic capacity and wheat yield

Abstract

Global warming is asymmetric, with the increase in temperature at night being greater than that during the day. The objectives of this study were to assess the effects of night warming during different growth stages on the wheat grain yield, dry matter accumulation and distribution, photosynthetic characteristics, and enzymes related to sucrose metabolism. For that, field experiments with passive night warming were conducted using local spring type cultivars ‘Yangmai 18′ and ‘Sumai 188′ and semi-winter type cultivars ‘Yannong 19′ and ‘Annong 0711′ in two growing seasons in the Yangtze River Basin of China (average night time temperature increases of 1.45 °C and 1.56 °C for 2019–2020 and 2020–2021, respectively). The cultivars were exposed to night warming between four different growth stages (tillering to jointing [NWT-J], jointing to booting [NWJ-B], and booting to anthesis [NWB-A]) after 50% of plants had attained the treatment-start stage (tillering: Zadoks growth stage 21, main shoot and one tiller; jointing: Zadoks growth stage 31, the 1st node was detectable; booting: Zadoks growth stage 41, flag leaf sheath extension stage; anthesis: Zadoks growth stage 60, the beginning of pollination). Plants grown under ambient conditions were considered as the control (NN). Treatment NWT-J increased dry matter accumulation in flag leaves and spikes at anthesis and maturity, ultimately benefiting the yield, and the increase was higher in the semi-winter type cultivars. NWT-J increased not only the chlorophyll content, photosynthetic traits (net photosynthetic rate, stomatal conductance, and transpiration rate), and the activities of the maximum efficiency of PSII photochemistry under dark-adapted wheat flag leaves at the grain-filling stage (14 days after anthesis) but also the activities of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphatase (FBPase), and glycolate oxidase (GOX), and thus improved the photosynthetic capacity of wheat flag leaves and facilitating photosynthate accumulation. NWT-J also increased sucrose-phosphate synthase activity in flag leaves at the grain-filling stage, which could improve sucrose content. Collectively, early vegetative night warming (warming during tillering-jointing) improved the photosynthetic capacity of the flag leaves during the grain-filling stage and promoted the post-anthesis accumulation of dry matter and the transfer of dry matter to the grains, which ultimately benefited the yield.