Plant Architecture and Flag Leaf Morphology of Rice Crops Exposed to Experimental Warming with Elevated CO₂

Projected increases in atmospheric CO₂ concentration ([CO₂]) and temperature (T∧a) have the potential to alter in rice growth and yield. However, little is known about whether T∧a warming with elevated [CO₂] modify plant architecture. To better understand the vertical profiles of leaf area index (LAI) and the flag leaf morphology of rice grown under elevated T∧a and [CO₂], we conducted a temperature gradient field chamber (TGC) experiment at Gwangju, Korea. Rice (Oryza sativa L. cv. Dongjin1ho) was grown at two [CO₂] [386 (ambient) vs 592 ppmV (elevated)] and three T∧a regimes [26.8 (almost equal to ambient), 28.1 and 29.8℃] in six independent field TGCs. While elevated T∧a did not alter total LAI, elevated [CO₂] tended to reduce (c. 6.6%) the LAI. At a given canopy layer, the LAI was affected neither by elevated [CO₂] nor by elevated T∧a, allocating the largest LAI in the middle part of the canopy. However, the fraction of LAI distributed in a higher and in a lower layer was strongly affected by elevated T∧a; on average, the LAI distributed in the 75-90 cm (and 45-60 cm) layer of total LAI was 9.4% (and 35.0%), 18.8% (25.9%) and 18.6% (29.2%) in ambient T∧a, 1.3℃ and 3.0℃ above ambient T∧a, respectively. Most of the parameters related to flag leaf morphology was negated with elevated [CO₂]; there were about 12%, 5%, 7.5%, 15% and 21% decreases in length (L), width (W), L:W ratio, area and mass of the flag leaf, respectively, at elevated [CO₂]. However, the negative effect of elevated [CO₂] was offset to some extent by T∧a warming. All modifications observed were directly or indirectly associated with either stimulated leaf expansion or crop phenology under T∧a warming with elevated [CO₂]. We conclude that plant architecture and flag leaf morphology of rice can be modified both by T∧a warming and elevated [CO₂] via altering crop phenology and the extent of leaf expansion.