Root respiration and phosphorus nutrition of tomato plants grown at a 36 degrees C root-zone temperature

Growth of tomato (Lycopersicon esculentum Mill.) plants decreases at root-zone temperatures (RZTs) >30 degrees C, but no research has been conducted on the effects of changes in root respiration on P acquisition at supraoptimal RZT. We monitored the changes every 3 to 5 days in root 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. Root respiration at 36 degrees C, however, increased from RZT initiation to day 8 and then decreased. Shoot P concentration and root phosphatase activity for plants grown at 25 OC did not change during the experiment. Shoot P concentration for plants at 36 degrees C, however, linearly decreased over time, and root phosphatase activity linearly increased over time. Decreased shoot growth and demand for P along with decreased root respiration after day 8 probably resulted in the decreased P uptake and shoot P concentration in plants grown at 36 degrees C RZT.