Plant root function under the gaseous environmental condition of medium in hydroponics.

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For a study on effects of gaseous environment in medium of hydroponics on plant root function, gas concentration in root media, such as sand, pumice stone and rockwool slab, was measured by using online sensor probes and a gas chromatograph system. Oxygen partial pressure and concentration of free inorganic carbon (gaseous CO_2 partial pressure) was able to be measured online. The thermal insulating sensor cover brought about accurate measurement of oxygen and carbon dioxide in the medium under the light condition. Even in the case of fluctuated water content in the medium, the gas partial pressure was able to be measured accurately. From the result of the experiment, it was found that water content in a certain medium could affect root aerial condition. But, very high oxygen partial pressure in the rockwool slab was maintained even after irrigation. It could be the reason that vigorous root and shoot growth was found in the horticultural crop planted in the rockwool slab.For some kinds of a very small amount of gases in the medium, we focused on the hydrocarbon gas, ethylene, and tried to measure using a gas chromatograph system. But, we were not able to obtain the accuracy necessary for quantitative analysis of ethylene accumulated in the medium. More effective method for sampling the very small amount of gases was necessary.From the results, methods of gas analysis on hydroponic medium could be useful for exact control of root environmental factors for optimization of environment for plant production in hydroponics.