Diffusion of Gases through Plant Tissues : Entry of Acetylene into Legume Nodules

I have measured acetylene diffusion through plant tissues including nodules from several species of legume—vetch, peas, soybeans, and Sesbania rostrata. The observed half-time for reequilibration of internal and external concentration is less than 1 minute for typical nodules. Inward diffusion of acetylene in air is rapid relative to the use of acetylene by nitrogenase so that diffusion of acetylene would not be a significant limiting factor for nitrogenase activity in air. However, under an atmosphere of Ar:O₂ where there is no N₂ reduction, the inward diffusion rate of acetylene into larger nodules could produce a measurable limitation of observed nitrogenase activity at low acetylene concentrations.