Effects of Temperature On Growth and Nutrient Uptake In Subterranean Clover During Recovery From Phosphorus Stress

Abstract

SummaryDuring a pretreatment period of 18 days, subterranean clover plants (Trifolium subterraneum L., cv. Mt. Barker) were grown at a deficient and an optimum phos· phorus supply in three temperature regimes (27°C dayj22°C night, 21jI6°C, 15jlOOC). They were then transferred to full solutions (optimum phosphorus) and plants from each pretreatment grown for a further 7 days in each of the three temperature regimes.Shoot dry weights and leaf areas at the end of pretreatment were greater the higher the temperature. However, the plants grown with a deficient phosphorus supply showed a smaller temperature response than the non·deficient control plants, suggesting an increase in phosphorus requirements at higher temperatures.Over the subsequent 7 days the relative growth rate of the previously deficient plants was smaller, and differed more from that of the non-deficient plants, the higher the temperature during pretreatment. Relative rates of leaf expansion over the same period were not influenced by differences in the phosphorus status at the beginning.For both phosphorus pretreatments the relative rates of increase in dry weight and in leaf area were smallest at the lowest temperature. Most of the effects of temperature and phosphorus nutrition on relative growth rates were reflected in similar, though somewhat smaller, effects on net assimilation rates.The distribution of dry matter to the roots was restricted after transfer of non-deficient plants from the highest to the lowest temperature and this was accompanied by a considerable accumulation of dry matter per unit leaf area. This did not occur in the plants recovering from phosphorus stress and the proportion of dry matter distributed to the roots was greater than in the non-deficient plants.It was concluded that differences in yield between levels of phosphorus supply, as well as growth responses after removal of a phosphorus stress, may be expected to decrease with a decrease in temperature.