Above-Optimum Temperature-Induced Differential Photosynthetic and Roots Morphometric Responses in Two Contrasting Rice Genotypes.

Temperature thresholds during the rice (Oryza sativa L.) cycle development have been reported to affect plant metabolism. Therefore, this study aimed to evaluate the effects of the above-optimal temperature on photosynthetic and morphometric parameters in two contrasting irrigated rice genotypes (BRS Querência—sensitive and Nagina 22 (N22)—tolerant). Plants of both genotypes were grown in rhizotrons and always maintained under two temperature conditions: Out—under environmental temperature conditions, and In—rhizotrons inside a plastic structure, which increased the temperature about 3 °C to 5 °C above the external one. In the genotype N22, there was an increase (twofold higher) in CO2 assimilation in plants cultivated under elevated temperature (In). In BRS Querência, the stomatal conductance (gs) and transpiration rate (E) decreased upon high temperature. The rise in the temperature also negatively impacted in the modulated fluorescence parameters in both genotypes. Increases in root dry weight (RDW) and shoot dry weight (SDW) were also observed in the genotype N22 when compared to BRS Querência upon temperature rise. In general, the N22 genotype showed greater response to the above-optimal temperature due to its intrinsic thermotolerance traits over BRS Querência. Thus, N22 appeared as a potential donor of heat tolerance genes aiming to obtain new cultivar to face current global warming.