Data_Sheet_1_A High-Yielding Rice Cultivar “Takanari” Shows No N Constraints on CO2 Fertilization.docx

Enhancing crop yield response to elevated CO2 concentrations (E-[CO2]) is an important adaptation measure to climate change. A high-yielding indica rice cultivar “Takanari” has recently been identified as a potential candidate for high productivity in E-[CO2] resulting from its large sink and source capacities. To fully utilize these traits, nitrogen should play a major role, but it is unknown how N levels influence the yield response of Takanari to E-[CO2]. We therefore compared grain yield and quality of Takanari with those of Koshihikari, a standard japonica cultivar, in response to Free-Air CO2 enrichment (FACE, +200 μmol mol−1) under three N levels (0, 8, and 12 g m−2) over three seasons. The biomass of both cultivars increased under E-[CO2] at all N levels; however, the harvest index decreased under E-[CO2] in the N-limited treatment for Koshihikari but not for Takanari. The decreased harvest index of Koshihikari resulted from limited enhancement of spikelet number under N-limitation. In contrast, spikelet number increased in E-[CO2] in Takanari even without N application, resulting in significant yield enhancement, averaging 18% over 3 years, whereas Koshihikari exhibited virtually no increase in yield in E-[CO2] under the N-limited condition. Grain appearance quality of Koshihikari was severely reduced by E-[CO2], most notably in N-limited and hot conditions, by a substantial increase in chalky grain, but chalky grain % did not increase in E-[CO2] even without N fertilizer. These results indicated that Takanari could retain its high yield advantage over Koshihikari with limited increase in chalkiness even under limited N conditions and that it could be a useful genetic resource for improving N use efficiency under E-[CO2].

提升作物在CO₂浓度升高（E-[CO₂]）条件下的产量响应，是应对气候变化的重要适应性举措。近期，高产籼稻（indica）品种‘高千穗（Takanari）’因兼具优异的库源容量，被认定为CO₂浓度升高环境下实现高生产潜力的潜在候选品种。为充分利用其上述性状，氮素应发挥关键调控作用，但目前尚不清楚氮素水平如何影响该品种对E-[CO₂]的产量响应。为此，本研究设置3个施氮水平（0、8和12 g m⁻²），在3个生长季内开展试验，对比了‘高千穗’与标准粳稻（japonica）品种‘越光（Koshihikari）’在自由大气CO₂富集试验（Free-Air CO₂ enrichment, FACE，+200 μmol mol⁻¹）条件下的籽粒产量与品质表现。两个供试品种的生物量在所有施氮水平的E-[CO₂]环境中均有所增加；但在氮素限制处理组中，‘越光’的收获指数在E-[CO₂]条件下出现显著下降，而‘高千穗’则未表现出该变化。‘越光’收获指数降低的原因在于，氮素限制条件下其穗粒数在E-[CO₂]环境中的提升幅度有限。与之形成鲜明对比的是，即便不施加氮肥，‘高千穗’的穗粒数在E-[CO₂]条件下仍显著提升，最终实现了平均18%的产量增益（3年试验均值）；而‘越光’在氮素限制条件下的E-[CO₂]环境中，产量几乎未出现提升。‘越光’的籽粒外观品质因E-[CO₂]出现严重劣化，在氮素限制与高温环境下尤为显著，表现为垩白粒占比大幅升高；但‘高千穗’即便不施氮肥，其垩白粒占比在E-[CO₂]条件下也未出现上升。上述研究结果表明，即便在氮素限制条件下，‘高千穗’仍能保持相较于‘越光’的高产优势，且籽粒垩白度仅小幅提升；同时该品种可作为提升CO₂浓度升高环境下氮素利用效率（N use efficiency）的优良遗传资源。