Root Respiration and Phosphorus Nutrition of Tomato Plants Grown at a 36 °C Root-zone Temperature

Growth of tomato ( Lycopersicon esculentum Mill.) plants decreases at root-zone temperatures (RZTs) >30 °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 °C RZT for 19 days. Root respiration rate in plants grown at 25 °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 °C, however, increased from RZT initiation to day 8 and then decreased. Shoot P concentration and root phosphatase activity for plants grown at 25 °C did not change during the experiment. Shoot P concentration for plants at 36 °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 °C RZT.