Effects of supplemental irrigation on the accumulation, distribution and transportation of 13C-photosynthate, yield and water use efficiency of winter wheat

Water resources are increasingly scarce, and droughts are frequent in the Huang-Huai-Hai Plain of China. There is an urgent need for developing water-saving technologies for winter wheat production in this region. Field experiments were carried out in silty loam soil from 2012 to 2014. Based on the same water condition in seeding period and the normal emergence of winter wheat, five supplemental irrigation (SI) regimes differing in the timing of SI were established. Crop development was categorized using the Zadoks scale. T1: no irrigation after emergence; T2: SI at jointing (4th node detectable, Z34); T3: SI at pre-wintering (average daily temperature drops to about 2 degrees and the wheat plant basically stops growing) and jointing; T4: SI at jointing and anthesis complete (Z69); T5: SI at pre-wintering, jointing and anthesis complete. The results showed that SI brought the soil water content in the 0-20 cm profile to 100% field capacity at the pre-wintering, jointing and anthesis complete stages of winter wheat, mainly improving the water supply condition in the 0-40 cm soil layer. Compared with no irrigation after emergence, SI at jointing and anthesis complete significantly increased grain yield by increasing the spike number, kernel number and grain weight. SI at the pre-wintering stage can improve grain number and yield under the condition of no SI at anthesis complete (comparing T3 with T2), but had no significant effect on grain yield when SI was supplied at jointing and anthesis complete (comparing T5 with T4), and even worse, the irrigation water use efficiency decreased. The decrease of water supply before anthesis complete significantly reduced the dry matter accumulation and photosynthetic rate at anthesis but promoted the translocation of photosynthates to the plant ear. SI at anthesis complete is advantageous for the assimilation of carbohydrates in the middle and late grain filling stage and for the distribution of those carbohydrates from vegetative organs to grain. These results indicated that SI at jointing and anthesis complete was conducive to coordinating the relationship between photosynthesis and photosynthates retranslocated after anthesis, and may improve the harvest index, grain yield and water use efficiency.