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Gas diffusion in bulky plant organs is relevant for understanding the respiratory metabolism. Limited tissue diffusivity due to low porosity may create gas concentration gradients leading to hypoxia. As porosity is known to be different between and within different tissues, oxygen (O2) diffusivity cannot be regarded as a homogeneous gas transport parameter of plant organs. This study aims to study the relationship between O2 diffusivity and porosity for four different horticultural products: eggplant, apple, turnip and pear, which have shown variability in tissue microstructure. Based on X-ray CT images of the whole product, porosity maps were created. O2 diffusivity was computed using a microscale model solved on the corresponding 3-D tissue microstructure of different samples across the product, derived from high resolution X-ray CT scan. The correlation between O2 diffusivity and porosity was determined along the radial tissue sample, as affected by sample size. The correlation was high in eggplant tissue (R2 = 0.96), compared to the other products. Distinct distribution of the O2 diffusivity to the porosity was also influenced by the characteristic of tissue intercellular space of the products such as tortuosity, connectivity and size of pore. In conclusion, the tissue diffusivity is not only influenced porosity, but also other microstructural parameters, and strongly affected by size of the considered tissue sample.