ABSTRACT

Atmospheric concentrations of carbon dioxide (CO₂) have steadily increased over recent decades. The fertilization effect of elevated CO₂ concentrations (E-[CO₂]) is known to increase the biomass production and also the nitrogen (N) demand of paddy rice, which affects the rice N use efficiency. This study was conducted to elucidate the fertilizer-derived N use of paddy rice (Oryza sativa L.) for two varieties, japonica cv. Koshihikari and indica cv. Takanari, with and without E-[CO₂] using a free-air CO₂ enrichment (FACE) facility in central Japan. To quantify the fate of fertilizer-derived N directly, polymer-coated ¹⁵N-labeled urea was used with a one-shot application rate of 80 kg N ha^–1 incorporated into the plowed layer at the basal fertilization before transplanting of rice seedlings. The biomass, total N concentrations, and ¹⁵N abundance in each part of the rice plants were measured at the panicle initiation, heading, and maturing stages. The total N content and ¹⁵N abundance in the soil were measured at the maturing stage to evaluate the N balance of the rice–soil system. While E-[CO₂] significantly increased the whole plant biomass and the total N content in panicles, it did not increase the total N and the fertilizer-derived N content in the whole plant. The recovery efficiency (fertilizer-derived N in the whole plant to applied N, RE) ranged between 64.9% and 68.7%, and the agronomic efficiency (fertilizer-derived N in panicles to applied N, AE) ranged between 37.8% and 43.8%. The effect of CO₂ on RE and AE was not significant. The REs, higher in Koshihikari, and the AEs, higher in Takanari indicated that Takanari preferentially allocated fertilizer-derived N to panicles. The REs, 69% at the maximum in this study, implies an upper limit of use efficiency of N fertilizer, even for polymer-coated (controlled-release) fertilizer. E-[CO₂] significantly increased the rice N uptake from sources other than fertilizer, of which mineralization was the most-likely source. Monitoring of soil fertility and appropriate fertilization management are, therefore, necessary for sustainable rice production avoiding long-term decline in soil N fertility.

摘要

近几十年来，大气中二氧化碳 (CO ₂ ) 的浓度稳步上升。已知升高的 CO ₂浓度 (E-[CO ₂ ])的施肥效应会增加水稻的生物量产量和氮 (N) 需求，从而影响水稻 N 的利用效率。本研究旨在阐明水稻 ( Oryza sativa L.) 两个品种（粳稻品种）的肥料衍生氮使用情况。越光和籼稻 cv。Takanari，使用和不使用 E-[CO ₂ ]在日本中部使用自由空气 CO ₂浓缩 (FACE) 设施。直接量化肥料衍生的氮的命运，聚合物涂层¹⁵使用 N 标记尿素，一次性施用 80 kg N ha ^–1，在水稻秧苗移栽前的基础施肥中将其掺入犁过的层中。在穗开始、抽穗和成熟阶段测量水稻植株各部分的生物量、总氮浓度和¹⁵ N 丰度。在成熟阶段测量土壤中的全氮含量和¹⁵ N 丰度，以评估水稻 - 土壤系统的氮平衡。虽然 E-[CO ₂] 显着提高了全株生物量和穗部全氮含量，但未提高全株全氮和化肥氮含量。回收效率（全株化肥氮对施氮、RE）在64.9%～68.7%之间，农艺效率（化肥氮对施氮、AE）在37.8%～43.8%之间. CO ₂对RE和AE的影响不显着。REs 在 Koshihikari 中较高，AEs 在 Takanari 中较高表明 Takanari 优先将肥料衍生的 N 分配给圆锥花序。REs，在本研究中最高为 69%，意味着氮肥使用效率的上限，即使是聚合物涂层（控释）肥料。E-[CO ₂] 显着增加了水稻从肥料以外的其他来源吸收氮，其中矿化是最可能的来源。因此，监测土壤肥力和适当的施肥管理对于可持续水稻生产避免土壤氮肥力的长期下降是必要的。