Effects of Dark Respiration on Dry Matter Production of Field Grown Rice Stand : Comparison of growth efficiencies in 1991 and 1992

Abstract

The dark respiration rates (Rr;CO₂ efflux rates per unit dry weight) in the whole plant, leaves, stems and panicles of rice, grown in the field, were measured in 1991 and 1992. In both years Rr in the whole plant was highest at the start of measurement (rooting stage), decreased rapidly thereafter until the heading time and then gradually during the ripening period. Rr in leaves after the end of leaf expansion and that in stems during the ripening period was nearly constant. This implies that Rr in the matured plant organs shows only a small variation. Although the temperature coefficient (Q₁0) of Rr was 2.06 on the average, it changed during the growth period and differed with the organ. The growth efficiency, GE=ΔW/(ΔW+R) (ΔW;increase of dry matter, R;respiratory loss) was above 60% during the early growth period, but decreased thereafter, and rapidly at the late ripening period. This decrease in GE is considered to have been caused by the increase in maintenance respiration which is not related to dry matter production. Although respiratory loss was almost the same in 199 1 and 1992, the GE at the late ripening stage was higher in 1992 (35%) with longer sunshine hours than in 1991 (5%). This means that decrease in GE was mainly caused by the decrease in gross photosynthesis. Translocation of large amount of carbohydrates was assumed to cause the decrease in GE of the whole plant.