環境に対する水稲の生育反応 : 第3報 日長と温度が生育と体内成分に及ぼす影響

抄録

Rice plants (CV. Norin-17) of vegetative stage (8.2 leaf-stage) were grown in five glass houses the temperature of them were differentially controlled under two photoperiods using natural light; long day (14-h light) and short day (9-h light). The day-night temperatures used were 35-30, 30-25, 25-20, 20-15, and 15-10°C. The plants of each house were sampled when they expanded five new leaves on main-stem (at 13.2 leaf-stage) to compare growth and chemical composition. As the day-temperature was maintained during light period and the night-temperature during dark period, the daily mean-temperature of each plot under long day was respectively 1°C higher than the corresponding plot under short day. 1) It took progressively longer time to reach a definite leaf-stage as the temperature decreased with slower leaf appearance rate. Plant height was highest at 25-20°C, being decreased at higher or lower temperatures. In general, tiller number increased as temperature decreased, although with a somewhat increase at 35-30°C and decrease at 15-10°C under short day. Both plant height and tiller number were greater under long day than under short day. 2) Dry weight of whole plant became greater as temperature decreased except that at 15-10°C under short day. The distribution of dry matter at leaf-blade was higher at higher temperatures, whereas at lower temperatures the roots weight became relatively greater. The dry matter percentage of leaf-blade and specific leaf weight (SLW) increased as temperature decreased, and there was found a minus correlation (r=-0.832**) between SLW and net assimilation rate (NAR). 3) The values of RGR (relative growth rate), RLGR (relative leaf area growth rate) and NAR were higher under long day than under short day. Under long day they were highest at 25-20°C or 30-25°C with a little decrease at 35-30°C and sharp decreases at lower temperatures, while under short day they showed a tendency to increase as temperature increased, except at 35-30°C where NAR decreased a little. Intimate correlations were found between RGR and RLGR, RGR and NAR with the correlation coefficients of 0.996*** and 0.924***, respectively. RLGR was strongly correlated with mean leaf appearance rate (r=0.982***). 4) Nitrogen concentration of shoots changed little by temperature treatments, but was higher under short day than under long day. Other elements, in general, decreased their concentrations at intermediate temperatures. The concentrations of total elements estimated tended to decrease with decrease of temperature. The total amounts of elements accumulated in the shoots paralleled dry matter accumulation. However, at higher temperatures Si, K, Ca + Mg, Mn, Fe, P, and S accumulated relatively more as com-pared with the accumulation of dry matter, and N and S accumulated relatively more at lower temperatures. K/N ratio increased but Mn/Fe ratio decreased with increase of temperature. 5) At leaf-blades, N concentration increased with decrease of temperature and under short day. At other organs the similar tendencies were found under short day, but under long day the concentrations were lower at intermediate temperatures. Non-protein soluble-N also increased with decrease of temperature at all plant parts, although with a little high value at 35-30°. TAC (total sugar + crude starch) concentration tended to increase with decrease of temperature. It was noticed that the dead leaf at low temperature had rather high nitrogen and TAC concentrations. C/N ratio (C:TAC, N: total-N) of whole plant increased under long day and with decrease of temperature.