ANTAGONISTIC EFFECTS OF ROOT-ZONE TEMPERATURE AND IRON ON PHOSPHORUS UPTAKE BY BUSH BEAN

Radiophosphorus (P-32) and hydroponically-grown bush bean were used to study P absorption kinetics as affected by root zone temperature (RZT ) and iron (Fe). Phosphorus uptake increased significantly (p < 0.05) at each successive 10 degrees C rise in RZT from 15 to 35 degrees C, a nd quadratic regression equations were highly correlated (R(2) = 0.98) between the uptake amount and exposure time. An estimated Q10 value o f 1.5, and the corresponding Arrhenius constant mu of 31 kJ/mol for P uptake were within range for a diffusion process in an aqueous solutio n. A concentration of 5 mu mol/L Fe significantly (p < 0.05) reduced P uptake from 6 h on at the RZTs studied, and Q10 and mu values were es timated at 1.2 and 14 kJ/mol, respectively.