Title: Discussion on appropriate positions for CO<SUB>2</SUB> enrichment within plant canopy by measurements of light intensity, CO<SUB>2</SUB> concentration, leaf area and photosynthetic rate in tomato grown by high-wire system
Abstract: This study aimed to discuss an effective technique of CO2 enrichment within a canopy of tomato grown by high-wire system in green house. Leaf area, photosynthetic photon flux density (PPFD), CO2 concentration and photosynthetic rate were measured at different height above ground level in the tomato canopy. The leaf area of the middle (1.2 to 1.8 m) and lower layer (0.6 to 1.2 m) was larger than that of the upper layer (1.8 to 2.2 m). The PPFD from the upper to lower layer was decreased from 370 to 45 μmol m-2 s-1 in winter. However, CO2 concentration varied little among the layers, and was below 400 μmol mol-1 during the day. The maximum photosynthetic rate (Pmax) of middle leaves was similar to that of upper leaves. The Pmax of lower leaves were less than a half of the other leaves. The photosynthetic rates of middle and lower leaves were increased by 1.2 to 1.3 times with elevated CO2 concentration from 400 to 800 μmol mol-1 under low PPFD (e.g., 125 μmol m-2 s-1). Thus, it was considered that elevating CO2 concentration at middle layer was appropriate for CO2 enrichment within a canopy of tomato grown by high-wire system.