Plant factors influencing phosphorus uptake by white clover from solution culture

Summary The phosphorus (P) uptake rate of several white clover populations was determined in two solution culture experiments. Populations and cultivars differed in P uptake per plant and per unit root length in both experiments. Correlation and multiple regression analysis showed that differences between populations for P uptake per plant were largely related (r²>80%) to differences in leaf area and absolute growth rate, when plants had been grown at high-P levels, and by differences in root size and absolute growth rate when plants had been grown at low-P levels. Differences between populations for P uptake per unit root length were related (r²≈50%) to leaf area and relative growth rate in experiment 1 and to transpiration rate and water influx in experiment 2, when plants were pretreated at high-P levels. Differences between populations for P uptake per unit root length were negatively related to root size when plants had been grown at low-P levels. On the basis of these and other results it is suggested that P uptake per plant is determined largely by shoot factors. However, P uptake per unit root length is negatively related to root size, because demand for P is largely determined by shoot factors, and so differences in root size lead to an apparent difference in uptake per unit of root size.