Mineral nutrition of tomato under diurnal temperature variation of root and shoot

Should root and shoot temperature vary in synchrony to optimize nutrient up take, particularly when there is a large difference in temperature from day to night (DIF) of air and soil? To answer this question, tomato (Lycopersi con esculentum Mill.) seedlings were grown in greenhouses with the air heat ed to give either a + 14 degreesC DIF or a +5 degreesC DIF in air temperatu re with a 16 degreesC mean. The root medium was either unheated except by t he air, or heated to 21 degreesC constantly, only in the day, or only in th e night. Experiments were repeated in early March and April in two years. O verall, growth was faster and there were higher concentrations of elements in leaves under +5 degreesC compared with + 14 degreesC air DIF, Root-zone heating significantly increased growth and nutrition, compared with no heat ing. There was a trend in growth and nutrient concentration with timing of root heating: constant > day > night. These differences in growth and nutri tion were similar under a +5 degreesC or +14 degreesC air DIF, and they wer e slight compared with no root zone heating. For most nutrients, coordinati on of root and shoot activity related to uptake and metabolism did not requ ire synchronous variation of air and soil temperature. Uptake and transport of nitrate was an exception. Heating roots in the day resulted in the high est nitrate concentration in leaves under a +14 degreesC air DIF, whereas h eating constantly was optimal under a +5 degreesC DIF. Our results indicate nitrate metabolism did benefit from synchronous variation in air and root temperature.