Studies on CO2 Exchange in Crop Plants : V. A newly devised "Infrared CO2-Analyser", and some of the results obtained by it, comparing the diurnal changes in photosynthetic rate in rice plants under an isolated condition with that under a community condition.

摘要

In connection with researches of physiology and ecology of crop plants, methods especially effectual for instantaneous and successive analysis of gases exchanged by growing plants have long been wanted by many investigators. Most of the devices hitherto known are more or less inaccurate and tedious though designed ingeniously, and not satisfactory for general uses in such researches. In the present report a negative type "Infraed gas analyser" newly devised by the authors is described. A schematic outline of the instrument together with its working principle is represented in Fig. 1. Infrared radiation send from a light source, of which the energy distribution is shown in the figure a, enters into the absorption cell, and is partially absorbed at λx, λy and λz by H2O, CO2 and other gases contained in sample air in the cell, respectively. Its distiibution of energy after absorption is changed as shown in the figure b. Then, the ray enters into the negative filter, consisting of two chambers, one containing 100% CO2 gas and the other N2 gas. The part of the ray passing through the former is strongly absorbed at the region, λx, its energy distribution being changed so as shown in the figure d, while the part passing through N2 gas in the latter chamber is not absorbed here at all, its distribution of energy being unaltered as shown in the figure c, which is almost similar in shape as the figure b. Each of the two parts of the ray falls finally on each junction D1 and D2, respectively, of the thermal detector, a thermopyle of differential type. The potential difference betwen the two junctions thus measured corresponds to the difference between the amount of energy absortion by 100% CO2 gas and that by the sample air; that is, to the shaded portion in the figure d. The larger the concentration of CO2 gas in the sample air, the smaller becomes the difference measured, no other gases than CO2 interfering with the measurement. The sample air is sucked by a pump alternately through either of the three ways, one for a blank test and the others for two replicated measurements of the air from the assimilation chamber, being turned from one to another by a gas switch which is operated electromagnetically and synchronized with the automatic allocation of the marking pen of a triple-ways recording voltmeter. Several examples of results obtained by the apparatus concerning the diurnal changes in photosinthetic activity of rice plants growning isolated in pots and of those growing in a community are presented.