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Reproductive allocation of an annual,<Emphasis Type="Italic"> Xanthium canadense</Emphasis>, at an elevated carbon dioxide concentration
Authors:Email author" target="_blank">Toshihiko?KinugasaEmail author  Kouki?Hikosaka  Tadaki?Hirose
Institution:(1) Graduate School of Life Sciences, Tohoku University, Aoba, 980–8578 Sendai, Japan
Abstract:Stimulation of vegetative growth by an elevated CO2 concentration does not always lead to an increase in reproductive yield. This is because reproductive yield is determined by the fraction of biomass allocated to the reproductive part as well as biomass production. We grew Xanthium canadense at low N (LN) and high N levels (HN) under an ambient (360 mgrmol mol-1) and elevated (700 mgrmol mol-1) CO2 concentration (CO2]) in open-top chambers. Reproductive yield was analysed as the product of: (1) the duration of the reproductive period, (2) the rate of dry mass acquisition in the reproductive period, and (3) the fraction of acquired biomass allocated to the reproductive part. Elevated CO2] increased the total amount of biomass that was allocated to reproductive structures, but this increase was caused by increased capsule mass without a significant increase in seed production. The increase in total reproductive mass was due mainly to an increase in the rate of dry mass acquisition in the reproductive period with a delay in leaf senescence. This positive effect was partly offset by a reduction in biomass allocation to the reproductive part at elevated CO2] and HN. The duration of the reproductive period was not affected by elevated CO2] but increased by HN. Seed production was strongly constrained by the availability of N for seed growth. The seed N] was very high in X. canadense and did not decrease significantly at elevated CO2]. HN increased seed N] without a significant increase in seed biomass production. Limited seed growth caused a reduction in biomass allocation to the reproductive part even though dry mass production was increased due to increased CO2] and N availability.
Keywords:Growth analysis  Nitrogen  Reproductive yield  Seed production
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