A new method to measure plant water uptake and transpiration simultaneously

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Abstract
A new weighing lysimeter system is described measuring transpiration and water uptake simultaneously on one plant, growing in water culture. The measurements may be made for short time intervals (min) making it possible to monitor quick responses to changing environmental conditions. Fresh weight change, a combination of growth and water status alterations in the plant, may be calculated from transpiration and water uptake. The system consists of two communicating vessels filled with nutrient solution; each placed on an electronic balance. One of these vessels carries the plant and is connected to the other by a flexible tube. Water uptake will cause an equal decrease of the solution level in each vessel. The weight decrease of the vessel with no plant provides a measure of water uptake, the total weight decrease on both balances represents transpiration. Test observations showed that measurements of transpiration and water uptake in a greenhouse can be made to an accuracy of about 0.03 g min−1 plant−1. With fluctuating radiation, a clearly radiation-dependent transpiration was measured on a tomato plant in a greenhouse. These measurements showed a delay between transpiration and water uptake. Consequently, fresh weight also fluctuated with radiation. An immediate decrease in transpiration was measured upon closure of a screen in the greenhouse, accompanied by an increase in fresh weight. From late afternoon until sunrise a constant fresh weight increase was measured; first at a relatively high rate probably due to growth and recovering from water deficits, thereafter at a constant rate probably only due to growth.

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