Photosynthesis of Buckwheat Population under Field Conditions with Special Reference to Planting Density

Abstract

Field experiments were conducted to characterize the canopy photosynthesis and the leaf photosynthesis at different layers in buckwheat under different planting densities. At the flowering stage, the canopy photosynthetic rate (Pn-canopy) was measured by means of a closed chamber system, and the leaf photosynthetic rate of each layer (Pn-layer) within the canopy was estimated using ¹³CO₂. The Pn-canopy showed maximum values at around noon: 19.7 and 27.4, μmol CO₂m^-2s^-1 at low (64 plants m^-2) and high (136 plants m^-2) planting densities, respectively, without light saturation at 1 800, μmol m^-2s^-1 of photosynthetically active radiation. The Pn-layer of uppermost layer showed maximum values of 21.4 and 20.4μmol CO₂m^-2s^-1 at low and high densities, respectively. The lower the layer, the lower the Pn-layer. The Pn-layer of low density was higher than that of high density at all layers. Leaves at the layer 40-60 cm above the ground level were assumed to contribute to Pn-canopy approximately 55% in both planting densities. The Pn-canopy of buckwheat was characterized to be promoted by having higher SLW and lower K at low and high planting density, respectively.