Effects of free-air CO 2 enrichment (FACE) and nitrogen (N) supply on N uptake and utilization of indica and japonica cultivars ( Oryza sativa L.)

Background Increasing atmospheric [CO 2 ] can increase photosynthesis and promote plant growth, consequently influencing nitrogen (N) cycling. Yet, there is no systematic information on the N response among different organs of japonica and indica rice genotypes to elevated [CO 2 ] as affected by N application. To investigate the impacts of elevated [CO 2 ] and N fertilization on N uptake and utilization of different genotypic rice ( Oryza sativa L.) during grain filling, a free-air CO 2 enrichment (FACE) experiment with indica cv. Liangyou 084 (IIY084) and japonica cv. Wuyunjing 23 (WYJ23) was conducted in Eastern China. Crops were exposed to ambient [CO 2 ] and elevated [CO 2 ] (200 μmol mol −1 above ambient) at two levels of N: control (0N) and 22.5 g N m −2 (normal N, NN), and they were sampled at 82 days after transplanting (DAT), 99 DAT, and maturity, respectively. Results Under FACE, significant declines of N concentration in all tissues and the whole plants were observed with the greater decrease in leaves and stems at three stages. Positive responses of N use efficiency (NUE) to elevated [CO 2 ] were recorded over the study period. The total N accumulation remained unchanged, while a large amount of N was partitioned to panicles at the expense of leaves and stems. As compared to WYJ23, greater N transportation from roots to aboveground, especially the panicles, was observed on IIY084 accompanied by higher panicle biomass (82 DAT and 99 DAT), N concentrations (maturity), and greater NUE for leaves through the study season. Across all [CO 2 ] and cultivars, N fertilization increased N partitioning to leaves and stems while decreasing that to panicles. Additionally, N supply decreased NUE while stimulating N concentrations and N amounts of rice plants. Among all treatments, IIY084 had the highest N accumulation and allocation in panicles under elevated [CO 2 ] in combination with N fertilizer at maturity. Conclusion Data from this study were helpful for understanding the temporal N uptake and utilization of different rice genotypes as affected by N availability and suggest that IIY084 promises a considerable prospect for its grain yield and quality under future elevated atmospheric [CO 2 ].