Effects of climate change on the protein content of wheat grains in China using Meta-analysis

Nutritional quality of cereals can depend mainly on the environmental factors subjected to climate warming in recent years. It is still lacking on the effects of the increase of CO₂ concentration, temperature, and precipitation caused by climate change on the nutritional quality of crops. In this study, a meta-analysis was performed on the existing literature data of various experimental sites. The protein content of wheat grains was combined with the meteorological parameters using a mixed linear model, fixed regression, and random residual analysis. A systematic evaluation was then made on the influence of key growth temperature on the protein content of wheat grains in the main wheat growing areas in China. A linear mixed model was used with the random intercept and slope in each region. The average sensitivity of grain protein content was calculated at the different stages of temperature (wheat total growth period temperature, vegetative growth period mean temperature and reproductive growth period mean temperature). The meta-analysis showed that the protein content in the wheat grain was significantly enhanced by warming (P<0.05), whereas, there was a significant decrease with the increasing CO₂ concentration. A complex variation was found in the precipitation of the protein content in the wheat grain. The increase in temperature partially offset the negative effects of CO₂ increase and precipitation on the wheat grain protein. Meanwhile, an upward trend was found in the average temperature in all provinces during the growth period of wheat from 2010 to 2018. Specifically, the average temperature increased by about 1.27 ℃ in the total growth period of wheat, indicating the different change trend of the average temperature in different wheat growing areas. The grain protein content in the different wheat-producing areas also responded positively to the average temperature in the growth period. The average temperature in the reproductive growth stage also dominated the variation in the protein content in the wheat grains. Some suggestions were proposed to fully meet the climate change in the different regions. The protein content of grains was significantly positively sensitive to the temperature (P<0.05) in Shandong, Jiangsu, and Anhui Provinces. A wheat-producing area can be expected to develop with a high protein content in grains under climate change. The climate shared a positively sensitive effect on the protein content of crops in Hebei, Henan, Shanxi, Shaanxi, Hubei, and Xinjiang, but there was no significant (P>0.05). The appropriate strategies of crop management were also formulated, according to the local conditions under environmental warming. The low protein content failed to plant the strong gluten wheat varieties in the middle and lower reaches of the Yangtze River, due to the low temperature and less sunshine during wheat filling. But the weak gluten varieties were planted with low protein content. The wheat with the low protein content was planted in Sichuan Basin for a long time, because of the low explanation of climate factors by grain protein content. The findings can provide the scientific basis for the influence of climate change on the protein content in wheat grains. A great contribution was also made to the regional decision-making and adaptation strategies for climate warming, in order to promote sustainable agriculture and nutritional security in China.