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.
Horticultural species vary in growth response to root-zone temperature (RZT) that exceed 30°C, but little is known about the effects of RZT on nutrient absorption. We determined the amount of phosphorus (P), zinc (Zn), and manganese (Mn) in plants of tomato (Lycopersicon esculentum Mill. 'Jet Star'), muskmelon (Cucumis melo L. 'Gold Star'), and thornless honey locust (Gleditsia triacanthos L. var. inermis Willd.) grown in an Hoagland No. 1 nutrient solution that was held at 24°, 27°, 30°, 33°, and 36°C RZT. Tomato dry mass and P and Mn contents were highest at 27°C RZT, but tomato Zn content did not show a response to RZT. Muskmelon dry mass and P, Zn, and Mn contents, however, were highest at 36°C. Honey locust dry mass and P and Zn contents did not vary with RZT, but honey locust Mn content decreased linearly with increasing RZT. Growth and P, Zn, and Mn absorption by muskmelon were increased by continuous exposure to RZT > 30°C, whereas honey locust growth and P, Zn, and Mn acquisition were not changed by exposure to RZT > 30°C. Growth and P, Zn, and Mn absorption by tomato, however, were decreased by continuous exposure to RZT > 30°C.
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