Chilling at grain filling stage reduced rice grain protein content: An experimental and modeling study

Abstract

Climate change has increased the trend in the intensity of global extreme weather events, including chilling. Nitrogen is one of the most essential nutrients for rice growth and development. Chilling will limit the uptake and translocation of nitrogen and the formation of grain protein in rice plants. The experiment conducted in the climate chamber with chilling stress applied at the grain filling stage revealed different effects on protein concentration in aboveground organs and caused asymmetry in grain protein contents (GPC) and grain protein yield (GPY). Chilling stress applied during the grain filling stage reduced the accumulation rate of rice grain protein by inhibiting the nitrogen uptake and the translocation from vegetative organs to grains, which resulted in a 35 % decrease in grain nitrogen accumulation and a 92 % increase in vegetative organs during grain filling. Consequently, the average nitrogen harvest index is reduced by 12 %. Nitrogen accumulation was severely affected when cooling degree days (CDD) ≥ 70 °C days. As the chilling intensity increased, the decrease of GPY was more significant than that of GPC. Moreover, we improved the grain temperature-nitrogen uptake function under chilling stress based on the relationship between CDD and the reduction in rice grains. By comparing the improved function and the modules in the existing crop model using the datasets from open field and artificial control experiments, we demonstrated that the current research on quantifying rice nitrogen uptake at extreme temperature stress needed further improvement. The effects of environmental stress on grain nitrogen accumulation are complex. Future studies should pay more attention to the ability of extreme temperature stress to affect nitrogen accumulation in various rice organs.