Effect Of Free Air CO₂ Enrichment (FACE) On Element Absorption And Alocation Of Rice (Oryza Sativa L.)

Global atmospheric carbon dioxide concentration ([CO₂])is increasing from 280 to 370μmol mol-1 since pre-industrial times and it is projected to reach levels of 450-550μmol mol-1 within year 2050. Elevated [CO₂] not only influences the growth, yield and quality of plants, but also changes the patterns of element uptake and allocation. Rice is the most important food crop in the world, however, to date, no information is available on the seasonal responses of element (include macro-elements and micro-elements) concentration, uptake and allocation of rice to elevated [CO₂]. In order to investigate the interactive effects of elevated [CO₂] and nitrogen (N) supply on seasonal changes in dry matter (DM) accumulation, element concentration, absorption and allocation, we conducted a unique free-air CO₂ enrichment (FACE) experiment in a rotation system of rice and wheat at Wuxi, Jiangsu, China (32°35.5'N, 119°42'E) in 2005–2006. A two line hybrid rice cultivar Lianyoupeijiu (LYPJ) was grown at ambient (AMB) or elevated (FACE, ca. 200 mmol mol^-1 above ambient) [CO₂] under two levels of N: low (LN, 12.5 g N m²) and normal (NN, 25 g N m2). The results obtained here could provide important implications on fertilizer managements and strategies of rice in a future elevated [CO₂] world.1. Average across the two rice seasons (i.e, 2005 and 2006), DM accumulation of rice in FACE plots was significantly increased by 16%, 20%, 18% and 17% on average at tillering, jointing, heading and maturity stages, respectively. Elevated N increased DM accumulation by 15%, 2%, 10% and 8% at tillering, jointing, heading and maturity stages, respectively, with the effect being significant at tillering and heading stage. However, interaction between [CO₂] and N for DM accumulation was not detected at all sampling stages.2. The overall patterns of changes in shoot element concentration through the growing season were similar across the two CO₂ treatments. The shoot N, P, K, Fe, Mn and Cu concentration exhibited a steady decrease with crop development, with minimum values reached at maturity stage. The Ca and Zn concentration increased from tillering to jointing stage and then decreased after that, with minimum values reached at maturity stage. Mg concentration was stable before heading, while it declined apparently after that. FACE decrased shoot N concentration by 11%, 11%, 13% and 9% at tillering, jointing, heading and maturity stages (P < 0.01), respectively, while FACE increased shoot P concentration by 9%, 20%, 13% and 16% at the respective stage (P < 0.01). FACE reduced the shoot Mg concentration at tillering and jointing stage, with no significant CO₂ effect deteced on other element (i.e., K, Ca, Fe, Mn, Cu and Zn) concentrations at different growth stages of LYPJ. Elevated N increased shoot N and P concentrations at heading and maturity stage, while for the most part, no N effect was detected on other element concentration through the growing season. In addition, interaction between [CO₂] and N for element concentrations were not detected at all sampling stages.3. The overall patterns of change in shoot element accumulation through the growing season were similar across the two CO₂ treatments. The shoot N, P, Ca and Mg accumulation increased with crop development, with maximum values reached at maturity stage. The shoot K, Fe and Cu accumulation increased from tillering to heading stage and then decreased after that, with minimum values reached at tillering stage. Mn and Zn accumulation increased with crop development, while it was stable after that. FACE increased shoot P accumulation by 27%, 45%, 34% and 36% at tillering, jointing, heading and maturity stages ( P < 0.01), respectively, and increased shoot Ca accumulation by 16% and 21% at tillering and jointing stage, respectively, and enhanced shoot K accumulation by 39% and 33% at jointing and maturity stage, respectively, while for the most part no significant CO₂ effect was observed on other element (i.e., N, Mg, Fe, Mn, Zn and Cu) accumulation at different growth stages. Elevated N increased shoot N and P accumulation at tillering, heading and maturity stage, as well as Mg accumulation at tillering and maturity stage, while for the most part, no N effect was detected on other element accumulation across the season. Interaction between [CO₂] and N for accumulation of all measured elements not detected at all sampling stages.4. The overall patterns of change in element allocation in stem through the growing season were similar across the two CO₂ treatments. The K, Ca distribution ratio in stem was stable across the season of LYPJ. The Fe, Mn and Cu distribution ratios in stem deceased with crop development, with maximum values reached at maturity stage. The N, P, Mg and Zn allocation in stem increased from tillering to jointing, then decreased after that. For the most part, no effect of FACE was found on element allocation in stem across crop development. Elevated N increased N allocation in stem at tillering, heading and maturity stage, while for the most part, no N effect was detected on other element allocation in stem across the growing season. In addition, no interactions between [CO₂] and N for element allocation in stem were not detected at all sampling stages.5. The overall patterns of change in element allocation in leaf through the growing season were similar across the two CO₂ treatments. The N, P, K, Ca, Mg and Zn distribution ratios in leaf deceased with crop development, while Fe distribution ratio in leaf showed an opposite trend. The Mn distribution ratio in stem was stable across the season, and Cu allocation in leaf increased from tillering to jointing, then decreased after that. For the most part, no effect of CO₂, N and their interaction was found on element allocation in leaf across crop development.6. The fractions of N, P, K, Ca, Mg, Fe and Cu in spike after heading had a sharp tendency to increase, while that of Mn and Zn was stable. The trend was similar for different treatments. FACE increase the the N fractions in spike by 28% and 4% at heading and maturity stage, respectively, while no effect of FACE was detected for other element fractions in spike (i.e., P, K, Ca, Mg, Fe, Mn, Zn and Cu). Elevated N increased N and Mg fractions in spike at maturity, decreased Zn fractions in spike at heading, while no effect of N was observed on other element fractions in spike at heading and maturity stage. With the exception of Zn fractions in spike at heading, no interactions between [CO₂] and N were not detected for element fractions in spike at heading and maturity stages...