Modifications in development and growth of a dual-adapted tropical rice variety grown as either a flooded or an aerobic crop

As the human population continues to grow and competition for natural resources increases, there is a consequent need to produce more food with fewer resources. Flooded rice crops use large quantities of water, which becomes scarcer for farmers. New methods of saving irrigation water have been tested and released but they often suffer from a yield trade-off. A comparative study was carried out with a recent dual-adapted variety cultivated as either a flooded transplanted crop or a direct-seeded and soil water-saturated crop, referred to as an aerobic crop, to dissect the crop physiological differences induced by crop management. Experiments were conducted at IRRI's experiment station in Los Banos, Philippines, in the dry seasons of 2011 and 2012. Grain yields were 2 tons/ha or 25% lower in the aerobic crop as a result of a complex series of modifications and adjustments in plant architecture and yield components. Four main changes higher plant density, slower rate of leaf appearance, lower nitrogen content, and reduced size of all organs induced by the aerobic crop environment were responsible for three chains of modifications that resulted in lower biomass accumulation and finally lower grain yield. Leaf appearance rates were bilinear in both environments, initially similar in both environments and slower after an inflection point that occurred at the appearance of the 8th leaf in a erobic crops instead of the 11th leaf in flooded crops. As a consequence, two fewer leaves were produced by main tillers in aerobic crops, whose individual leaf area thus was much lower. In 2012, plant nitrogen content was about 1% lower in the aerobic crop than in the flooded crop during the entire crop duration. Biomass accumulation of the variety used was biphasic in both environments, with high radiation use efficiency during the two phases of effective biomass accumulation in flooded crops, and the standard radiation use efficiency expected with C3 species in aerobic crops during the same phases.随着全球人口持续增长、自然资源竞争愈发激烈，人类亟需在资源投入缩减的前提下提升粮食总产量。淹水种植的水稻耗水量极高，而农户可获取的水资源正日益稀缺。当前已有多项节水灌溉新技术完成测试并得以推广，但这类技术往往伴随着产量权衡。 本研究针对一款新近育成的双适应性水稻品种开展对比试验，该品种既可采用淹水移栽种植模式，也可采用直播且土壤维持水分饱和的旱作栽培（aerobic crop）模式，旨在剖析不同种植管理方式诱导的作物生理差异。试验于2011年与2012年旱季，在菲律宾洛斯巴诺斯的国际水稻研究所（IRRI）试验站展开。 试验结果表明，旱作栽培模式下的稻谷产量较淹水种植模式低2吨/公顷，降幅达25%，这一现象源于植株株型与产量构成要素的一系列复杂调控与适应性调整。旱作环境诱导产生的四大核心变化——更高的植株密度、更慢的叶片出叶速率、更低的植株氮素含量以及各器官尺寸减小，共同引发了三条调控通路，最终导致生物量积累降低，进而造成稻谷产量下降。 两种种植模式下的叶片出叶速率均呈双线性特征，前期两者出叶速率基本一致，但在拐点出现后速率显著放缓；旱作栽培模式的拐点出现在第8片叶展开时，而淹水种植模式的拐点则出现在第11片叶展开时。受此影响，旱作栽培模式下主茎分蘖的总出叶数较淹水模式少2片，单叶面积也大幅降低。2012年的测定数据显示，在整个生育期内，旱作栽培模式下植株的氮素含量较淹水种植模式低约1%。 供试品种的生物量积累在两种种植模式下均呈双相特征：淹水种植模式在两个有效生物量积累阶段均表现出较高的辐射利用效率；而旱作栽培模式在相同阶段的辐射利用效率则符合C3植物的标准辐射利用效率水平。