HOW TREE ROOTS GATHER OXYGEN FROM SOIL FOR ENERGY SUPPLY BY RESPIRATION

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 ab ove the soil surface and in contact with the external atmosphere. A ne t convective volume flow of gas from the soil into the roots and out o f the stump is observed if the mean molar mass of the gas present in t he soil is lower than that present in the intercellular space of the r oots. The direction of the convective gas flow can be reversed by incr easing the molar mass of the gas present in the soil. These phenomena are governed by Graham's law of diffusion. They demonstrate the import ance of gas convection for the gas exchange in tree roots.