開放系大気CO_2増加(FACE)実験による作物の高CO_2応答の解明

概要

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It is well known that increasing CO_2 concentration stimulates plant photosynthesis at the short-term scale. To understand plant responses to elevated CO_2 concentration at the long-term scale under the field conditions, free-air CO_2 enrichment (FACE) experiments have been conducted for various crop species. The FACE experiments have shown that photosynthetic capacity often, but not always, declined during the prolonged exposure to elevated CO_2, known as an acclimation response. At the whole plant scale, rice biomass was stimulated by elevated CO_2 during the early growth stage, but stimulation ratio gradually decreased with the plant stage. The early growth stimulation could be related with enhanced nitrogen uptake, leaf area expansion and canopy photosynthesis. As the growth stage progressed, a decrease in leaf nitrogen concentration became obvious under FACE conditions, and stimulation ratios of biomass, nitrogen uptake and leaf area were gradually declined. The mechanisms of these acclimation responses are still uncertain, but nitrogen status of the whole plant plays a major role. In addition, the concepts of sink-source or carbon-nitrogen balance are useful for understanding the mechanisms of acclimation response to elevated CO_2, but need to be tested quantitatively by using the FACE systems and mechanistic crop growth models.
2012-05-31