How respiratory gas diffusivity correlates with porosity of plant organ tissues

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 tree different horticultural products: eggplant, apple, and turnip, which have shown variability in tissue microstructure. Based on X-ray CT images, porosity maps of the whole fruit and vegetable have been previously 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 region of interest (ROI) size. The correlation was strong in eggplant tissue (R² = 0.95), compared to the other products. Distinct distribution of the O₂ diffusivity to the porosity was influenced by the physical characteristic of tissue intercellular space. The reduced ROI size changed the O₂ diffusivity-porosity relationship, caused by the change in physical structure of the tissue. In conclusion, the tissue diffusivity did not linearly link to the porosity, other microstructural parameters and the size of the considered tissue sample affected the correlation.