How Tree Roots Gather Oxygen from Soil for Energy Supply by Respiration

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Abstract
The gas exchange between the root system of the European alder (Alnus glutinosa (L.) Gaertn.) and the surrounding soil is studied using four-year-old trees. For the experiments the root system connected to its stump is exposed to gases of different molar mass. The stump is cut above the soil surface and in contact with the external atmosphere. A net convective volume flow of gas from the soil into the roots and out of the stump is observed if the mean molar mass of the gas present in the soil is lower than that present in the intercellular space of the roots. The direction of the convective gas flow can be reversed by increasing the molar mass of the gas present in the soil. These phenomena are governed by Graham 's law of diffusion. They demonstrate the importance of gas convection for the gas exchange in tree roots.

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