Combined effect of elevated CO2 and temperature on dry matter production, net assimilation rate, C and N allocations in tropical rice (Oryza sativa L.)

A field experiment was carried out for 3 years to observe the effects of ambient CO2 (390 μmol mol−1 in open field (UC) as well as control chamber (CC)), elevated CO2 (EC) (550 μmol mol−1) and elevated CO2 (550 μmol mol−1) + elevated temperature (+2 °C over control chamber) (ECT) on dry matter (DM) production, carbon (C) and nitrogen (N) concentrations in plant parts and its allocation in a tropical rice cultivar (cv. Naveen, photoperiod non-sensitive) under open top chambers (OTCs). Highest increase (84.5%) in DM accumulation in the above ground portion was noticed under ECT than that under CC at the panicle initiation stage over three kharif cropping season. Root biomass, leaf area index (LAI) and net C assimilation rates (NAR) increased significantly under EC than CC by 28, 19 and 40%, respectively. The grain yield was also significantly higher under EC compared to CC (22.6%), although the higher temperature in ECT reduced the yield advantage by 3% than EC over 3 years. The C concentrations in stem, leaves and roots were highest at the heading stage and increased significantly by 5, 4.8 and 4.9% in stem, leaves and roots, respectively under EC over CC. The net C yield increased both under EC and ECT by 23.3 and 24.2% than CC over the period of 3 years, respectively. The order of C and N allocations in different plant parts was panicles > root > stem > leaves. The N use efficiency for grain increased significantly under EC.

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► The net C yield in plant increased under elevated CO2 by 23.3% over ambient CO2.
► Grain N use efficiency decreased under elevated CO2 + temperature than elevated CO2.
► Elevated CO2 + temperature upset yield advantage of elevated CO2 alone in rice.
► Net assimilation rate increased in elevated CO2 by 40% than ambient CO2.
► Elevated CO2 increased tissue C and decreased tissue N concentrations.