Effects of warming on the protein content of winter wheat grains under the conservation tillage

Abstract: Winter wheat (Triticum aestivum L.) is one of the major food crops in the world. Climate warming has dominated the growth and yield of winter wheat, particularly the protein formation and content of grains. But, the effects of warming on the protein content still remain unclear so far. Taking "Ji Mai 22" as the test material, this study aims to determine the specific effects of climate warming on the winter wheat growth and development, yield, and grain protein content. Climate warming was also simulated with an infrared warming device. Field warming experiments were conducted under the No Tillage (NT), and Conventional Tillage (CT) in the North China Plain for three consecutive years (2017-2019). The results showed that the open field warming reduced the overwintering period, indicating a significant shift in the regreening period. The nutritional growth period was then prolonged for the nitrogen accumulation time in the pre-anthesis period of plants. There was an increase in the Leaf Area Index (LAI) at the regreening-anthesis period, the net photosynthetic rate at the regreening-maturity period, and the aboveground dry mass of winter wheat. 20.17% (CT) and 99.21% (NT) of nitrogen accumulation in the winter wheat stems and leaves at the anthesis period, respectively, whereas, 24.62% (CT) and 134.21% (NT) of nitrogen transfer in the stems and leaves after anthesis increased by the warming in 2019, and the contribution of nitrogen in the stems and leaves contribution to seeds increased by 2.43% (CT), and 46.10% (NT). The NT warming increased the yield, where the NT yield was on average lower than that of CT. The CT yield of warmed winter wheat decreased by 2.14% and 4.62% in 2017 and 2018, respectively, and increased by 7.05% in 2019, whereas, the NT yield increased by 5.54% (2017), 34.44% (2018), and 42.25% (2019), respectively. The winter wheat yield in 2018 was significantly lower than that in 2017 and 2019. The reason was that the excessive precipitation in spring inhibited the winter wheat growth and development, leading to less yield in 2018. The temperature greatly contributed to the protein content of winter wheat grains, with an average increase of 14.28% (CT) and 17.39% (NT) for three consecutive years, compared with the control group. Therefore, the temperature promoted the conversion of nitrogen to the grain via the physiological characteristics of winter wheat. The reduction in effective spikelets number allowed the nitrogen for more grains to enter the final effective grain number, thus significantly increasing the grain protein content at high temperatures. The soil temperature under the NT was lower than that under the CT. The soil temperature was slower to rise in early spring, which affected the greening and early growth of wheat, resulting in the lower initial values of LAI, and net photosynthetic rate of winter wheat under the NT. The NT under the warming treatment reduced the post-anthesis soil temperature, but increased the soil water content, indicating the better wheat growth under a high post-anthesis temperature environment, compared with the CT. There was no significant difference in the grain protein content between CT and NT. This finding can provide a strong reference for the effect of climate warming on the protein content of winter wheat seeds under conservation tillage.