A Null-Point Compensating System for Simultaneous and Continuous Measurement of Net Photosynthesis and Transpiration by Controlled Gas- Stream Analysis
A method is described by which the exchange of water vapor and CO2 between the intact plant and its atmospheric environment can be continuously, simultaneously, and independently measured with a high degree of accuracy. Measurement is achieved by inclosing the shoot (or part of it) in a chamber and continuously compensating for the changes which the activity of the plant makes in the composition of the chamber atmosphere. The rate of compensation measures the processes directly. Accuracy is increased by using a hygrometer and a CO2 analyzer as null-point indicators. The method permits efficient control of the atmospheric environment of the shoot, since the concentrations of CO2, water vapor, and O2 can be independently controlled within wide ranges. The entire apparatus is capable of operation in a mobile laboratory independent of stationary facilities.