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Title: Acclimation of Nitrogen Uptake Capacity of Rice to Elevated Atmospheric CO2 Concentration

Author
item SHIMONO, HIROYUKI - NARCT, IWATE, JAPAN
item Bunce, James

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2008
Publication Date: 1/1/2009
Citation: Shimono, H., Bunce, J.A. 2009. Acclimation of Nitrogen Uptake Capacity of Rice to Elevated Atmospheric CO2 Concentration. Annals Of Botany. 103:87-94.

Interpretive Summary: Plants grown at elevated concentrations of carbon dioxide generally have lower concentrations of nitrogen, for reasons which are not known. The lower concentration of nitrogen reduces their nutritional value. In this study of rice, we found that slower rates of nitrogen uptake from the soil for plants at elevated carbon dioxide were caused by reduced rates of delivery of nitrogen from the soil to the plants roots, because of slower rates of water uptake by the plants at elevated carbon dioxide. This work will be of interest to scientists trying to maintain the nutritional value of crops in spite of rising atmospheric carbon dioxide concentrations.

Technical Abstract: Nitrogen is one of the major variables affecting the response of crop yields to elevated carbon dioxide. Elevated carbon dioxide increases root size, but there are no consistent reports of carbon dioxide effects on nitrogen uptake rates per unit of root. We proposed a simple concept for analysing treatment effects on the nitrogen uptake of plants. Total nitrogen uptake, determined by the rate of depletion of nitrogen from the nutrient solution, was divided into two factors: (1) photosynthesis-driven or "active" uptake, and (2) transpiration-driven or "passive" uptake. Passive uptake was calculated from the amount of nutrient solution transpired and the average concentration of nitrogen in the nutrient solution during the observation, and active uptake was calculated from the total minus the passive uptake. In a short-term experiment, we exposed rice plants to three levels of carbon dioxide for a day. Higher carbon dioxide increased leaf photosynthesis and decreased leaf stomatal conductance. While active nitrogen uptake was slightly increased under higher carbon dioxide, passive uptake was substantially decreased. Consequently, total nitrogen uptake was decreased with carbon dioxide, and there was a close correlation between total uptake and plant transpiration rate. In a long-term experiment, we grew rice at ambient and elevated carbon dioxide from sowing to maturity. Elevated carbon dioxide increased leaf photosynthesis throughout the season. Shoot and root dry weights were higher in elevated carbon dioxide. Active nitrogen uptake sharply decreased with age, but was not much affected by carbon dioxide. Passive nitrogen uptake was lower in elevated carbon dioxide. Again, there was a close correlation between total nitrogen uptake and plant transpiration rate. Our results suggest that the decreased transpiration at elevated carbon dioxide is a key factor reducing nitrogen uptake.