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 (Ta) have the potential to alter in rice growth and yield. However, little is known about whether Ta 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 Ta 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 Ta regimes [26.8 (≈ambient), 28.1 and 29.8℃] in six independent field TGCs. While elevated Ta 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 Ta, 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 Ta; 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 Ta, 1.3℃ and 3.0℃ above ambient Ta, 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 Ta warming. All modifications observed were directly or indirectly associated with either stimulated leaf expansion or crop phenology under Ta warming with elevated [CO2]. We conclude that plant architecture and flag leaf morphology of rice can be modified both by Ta warming and elevated [CO2] via altering crop phenology and the extent of leaf expansion.