[A-CG30] Material circulations in Terrestrial Ecosystem: Water, Carbon and Nitrogen etc.

[ACG30-16] Model-Aided Analysis of FACE Effects on Rice Canopy Photosynthesis, Transpiration, and Water Use Efficiency

*Hiroki Ikawa¹, Hiroki OUE², Mayumi YOSHIMOTO¹, Kazuhiko KOBAYASHI³, Masumi OKADA⁴ (1.National Institute for Agro-Environmental Sciences, 2.Faculty of Agriculture, Ehime University, 3.Graduate School of Agricultural and Life Sciences, The University of Tokyo, 4.National Agricultural Research Center for Tohoku Region)

Sustainable agricultural practice requires promising crop productivity with efficient water use. Given the projected increase in atmospheric CO₂ concentration [CO₂], our understanding on the CO₂ effects on rice productivity (i.e., photosynthesis) and water use (i.e., transpiration) on a leaf scale improved in the last few decades, particularly with Free-Air CO2 Enrichment (FACE) experiments that enable a simulation of a future agricultural field with high [CO₂]. However, very few information is yet available as to how the investigation on a leaf-level response of photosynthesis and transpiration to [CO₂] is translated to the whole canopy photosynthesis and transpiration (Shimono et al., Glob. Change Biol., 2013; Yoshimoto et al., Agric. For. Meteorol., 2005). This is partly due to the limited size of a FACE ring where it is difficult to apply top-down measurements, such as the eddy covariance technique. In this study, we quantified the effect of [CO₂] on rice canopy photosynthesis, transpiration and water use efficiency, using a multi-layer model with the model parameters obtained from single-leaf photosynthesis and transpiration measurements. With the model parameters carefully determined, we delineated the effects of [CO₂] on the canopy photosynthesis and transpiration through the changes in physiological and micrometeorological conditions for a better understanding on future rice productivity and water use.