ROOT RESPIRATION AND PHOSPHORUS-NUTRITION OF TOMATO PLANTS GROWN AT A36-DEGREES-C ROOT-ZONE TEMPERATURE

Growth of tomato (Lycopersicon esculentum Mill.) plants decreases at r oot-zone temperatures (RZTs) >30 degrees C, but no research has been c onducted on the effects of changes in root respiration on P acquisitio n at supraoptimal RZT. We monitored the changes every 3 to 5 days in r oot respiration, root surface phosphatase activity, and P acquisition of 'Jet Star' tomato plants grown in Hoagland's no. 1 solution held at 25 and 36 degrees C RZT for 19 days. Root respiration rate in plants grown at 25 degrees C increased linearly from RZT initiation to day 12 , but there was no difference in respiration between days 12 and 19. R oot respiration at 36 degrees C, however, increased from RZT initiatio n to day 8 and then decreased. Shoot P concentration and root phosphat ase activity for plants grown at 25 OC did not change during the exper iment. Shoot P concentration for plants at 36 degrees C, however, line arly decreased over time, and root phosphatase activity linearly incre ased over time. Decreased shoot growth and demand for P along with dec reased root respiration after day 8 probably resulted in the decreased P uptake and shoot P concentration in plants grown at 36 degrees C RZ T.