*Article* **Season A**ff**ects Yield and Metabolic Profiles of Rice (***Oryza sativa***) under High Night Temperature Stress in the Field**

**Stephanie Schaarschmidt 1, Lovely Mae F. Lawas 1,2,**†**, Ulrike Glaubitz 1, Xia Li 1,3, Alexander Erban 1, Joachim Kopka 1, S. V. Krishna Jagadish 2,4, Dirk K. Hincha <sup>1</sup> and Ellen Zuther 1,\***


Received: 6 March 2020; Accepted: 29 April 2020; Published: 30 April 2020

**Abstract:** Rice (*Oryza sativa*) is the main food source for more than 3.5 billion people in the world. Global climate change is having a strong negative effect on rice production. One of the climatic factors impacting rice yield is asymmetric warming, i.e., the stronger increase in nighttime as compared to daytime temperatures. Little is known of the metabolic responses of rice to high night temperature (HNT) in the field. Eight rice cultivars with contrasting HNT sensitivity were grown in the field during the wet (WS) and dry season (DS) in the Philippines. Plant height, 1000-grain weight and harvest index were influenced by HNT in both seasons, while total grain yield was only consistently reduced in the WS. Metabolite composition was analysed by gas chromatography-mass spectrometry (GC-MS). HNT effects were more pronounced in panicles than in flag leaves. A decreased abundance of sugar phosphates and sucrose, and a higher abundance of monosaccharides in panicles indicated impaired glycolysis and higher respiration-driven carbon losses in response to HNT in the WS. Higher amounts of alanine and cyano-alanine in panicles grown in the DS compared to in those grown in the WS point to an improved N-assimilation and more effective detoxification of cyanide, contributing to the smaller impact of HNT on grain yield in the DS.

**Keywords:** high night temperature; rice; grain yield; wet season; dry season; metabolomics
