Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
J Exp Bot. 2013 Aug;64(11):3179-88. doi: 10.1093/jxb/ert154.
Rising atmospheric CO₂ concentrations will probably increase rice (Oryza sativa L.) yield but decrease grain nitrogen (GN) concentration. Grains attached to different positions in the panicles differ greatly in weight and quality, but their responses to elevated CO₂ (e[CO₂]) are poorly understood, which limits our understanding of the mechanisms of yield enhancement and quality degradation. Thus a free-air CO₂ enrichment experiment was conducted to examine the effects of e[CO₂] on grain mass (GM), grain carbon (GC), and GN accumulation in the spikelets attached to the upper primary rachis branch (superior spikelets; SS) and those attached to the lower secondary rachis (inferior spikelets; IS). e[CO₂] stimulated the rice yield by 13% but decreased the N concentration in the panicle by 7% when averaged over two levels of N fertilizations (P < 0.01). The responses of SS and IS to e[CO₂] were different particularly under higher N supply. For SS, e[CO₂] decreased GN by 24% (P < 0.01) but did not affect GM. For IS, e[CO₂] increased GM by 13% (P < 0.05) but GN was not affected. The reduction of GN due to e[CO₂] started to appear at the beginning of grain filling. These results suggest that future [CO₂] levels probably stimulate the grain growth of IS, most of which are not marketable due to limited size, at the expense of GN reduction in SS. Translocation of N from SS to IS may be a possible mechanism for reduction in GN of SS. This may degrade the grain quality of marketable rice under e[CO₂].
大气中二氧化碳浓度的升高可能会增加水稻（Oryza sativa L.）的产量，但会降低籽粒氮（GN）浓度。稻穗不同部位的籽粒在重量和质量上差异很大，但它们对高浓度二氧化碳（e[CO₂]）的反应知之甚少，这限制了我们对产量提高和质量下降机制的理解。因此，进行了一项自由空气 CO₂ 富集实验，以研究 e[CO₂]对穗上主枝（上部颖花；SS）和穗下二次枝（下部颖花；IS）上附着的小穗粒重（GM）、粒碳（GC）和 GN 积累的影响。e[CO₂]在两种氮施肥水平下平均使水稻产量提高了 13%，但使穗部氮浓度降低了 7%（P < 0.01）。SS 和 IS 对 e[CO₂]的反应在高氮供应下尤其不同。对于 SS，e[CO₂]使 GN 降低了 24%（P < 0.01），但 GM 不受影响。对于 IS，e[CO₂]使 GM 增加了 13%（P < 0.05），但 GN 不受影响。由于 e[CO₂]导致 GN 减少的现象从灌浆开始就开始出现。这些结果表明，未来的[CO₂]水平可能会刺激 IS 的籽粒生长，由于尺寸有限，大部分 IS 的籽粒是不可销售的，而 SS 的 GN 则会减少。从 SS 向 IS 转移 N 可能是 SS 中 GN 减少的一个可能机制。这可能会降低 e[CO₂]下可销售水稻的籽粒质量。
