Meta-analysis of rice yield and grain quality under high temperature: Effects of intensity, magnitude, timing, environment, and growth stage

Abstract

High-temperature stress (HT) increasingly threatens rice yield and grain quality under global warming. Variability in experimental conditions, and growth stages, however, limits our understanding of HT effects. To address these limitations, we conducted a meta-analysis based on 315 observations from 61 globally distributed studies to evaluate the effects of temperature increase, diurnal warming patterns (daytime-only, nighttime-only, and synchronous diurnal warming), and growth stage on rice yield and grain quality across cultivation systems. Our results show that: (1) seed-setting rate decreases progressively with warming, whereas spikelets per panicle exhibit a threshold response, declining significantly only when high temperature exceeds 32℃, whereas panicle number and thousand-grain weight were less affected, indicating that maintaining spikelet development and fertility is crucial for enhancing thermotolerance; (2) pot experiments under controlled conditions exaggerate the negative impacts of HT on rice milling and appearance quality relative to field studies; (3) synchronous diurnal warming exerted stronger adverse effects on seed-setting rate and grain chalkiness than either daytime-only or nighttime-only warming; and (4) HT during the seedling and tillering stages promoted dry matter accumulation, whereas HT after heading substantially reduced biomass, panicle traits, and grain quality. This meta-analysis quantifies the effects of high-temperature stress on rice yield, as well as appearance, milling, nutritional, and cooking quality traits, providing evidence-based guidance for developing adaptive agronomic practices.