Developmental and morphological responses of rice to elevated atmospheric CO_2 concentration

CO_2浓度升高对水稻生长的促进作用可能是由水稻的生长发育性状和形态性状介导的。关于水稻光合作用的研究已经很多，但对CO_2浓度升高对水稻形态建成的影响还不清楚。因此，我们试图研究CO_2浓度升高（高于环境浓度200μmol/mol）对不同成熟度和不同株型水稻品种生长发育和形态的影响。实验采用自然光照生长箱和自由空气CO_2富集（FACE）装置。CO_2浓度升高使中熟品种的抽穗期提前，但对早熟品种的生长发育没有促进作用。叶片长度对CO_2浓度升高的反应在基因型间也存在差异，早熟品种表现出显著的正效应，而中等品种表现出显著的负效应。叶片外观和叶片长度的CO_2响应的基因型差异主要发生在穗分化后发育的上部3 ~ 4片叶片。结果表明，基因型× CO_2对生育期的互作可以影响叶片数和叶片大小，而叶片数和叶片大小与水稻生产力有直接关系。我们还利用一个小穗数有限的突变体，检验了穗大小的基因型差异是否影响其对CO_2浓度升高的生长反应。一个亲本及其突变体表现出相似的生长促进效应，尽管突变体每穗小穗数仅为50- 60%，但小穗数有限本身并不限制生长促进效应。在所有试验中，CO_2浓度升高引起的光合反应的基因型差异主要是由于叶片绿度或氮含量的差异。结果表明，CO_2浓度升高引起的生长反应的基因型差异主要归因于与发育和氮营养相关的性状。

Growth enhancement of rice by elevated CO_2 can be mediated by the developmental and morphological traits. Much has been studied for the photosynthetic responses but understandings on the effects of elevated CO_2 on morphogenesis of rice are still limited. We therefore attempted to determine the effects of elevated CO_2 (200μmol/mol above ambient) on development and morphology or rice varieties differing in maturity and plant types. Naturally sun-lit growth chambers and free air CO_2 enrichment (FACE) facilities were used for the experiments. Elevated CO_2 advanced heading dates of medium maturing varieties but did not foster development of two early varieties. A contrasting response of lamina length to elevated CO_2 was also observed among the genotypes ; a significant positive effect was found in early varieties but a negative one in medium varieties. The genotypic difference in CO_2 responses of leaf appearance and lamina length occurred mainly in the upper three to four leaves, which developed after panicle initiation. The results suggest that the genotype x CO_2 interaction on the developmental time can influence leaf number and lamina size which have a direct relevance to the rice productivity. We also tested whether genotypic difference in panicle size influences the growth responses to elevated CO_2 using a mutant with limited spikelet number. A parent and its mutant showed a similar growth enhancement due to elevated CO_2 despite the mutant having only 50-60 % of spikelet number per panicle, suggesting that limited spikelet per se does not limit growth enhancement. In all experiments, genotypic variation in photosynthetic responses to elevated CO_2 was mainly due to the difference in leaf greenness or nitrogen content. The results suggest that genotypic variation in growth responses to elevated CO_2 can mostly ascribed to the traits associated with development and nitrogen nutrition.