Heterogeneity of a leaf for radiative transfer : poster

Popular radiative transfer models (PROSPECT, Fluspect) represent mesophyll of leaves as a homogeneous medium of pigments and water. However, mesophyll of many leaves is heterogeneous. The aim of the work was to analyse how significant the difference in optical properties between two sides of a leaf is. The key question was: Is possible to retrieve extra plant traits by adding additional data – optical properties of the abaxial side? We surveyed three-five leaves of six species: two Monocots and four Dicots. Leaves were fixed in a FluoWAT leaf clip and optical properties (reflectance and transmittance) were recorded for both sides of each leaf with ASD spectroradiometer under solar light. The spectral data was used to invert the radiative transfer model Fluspect and retrieve leaf traits. We were able to validate accuracy of the retrieval for chlorophyll and carotenoid concentrations, as we measured them by extraction right after the spectral measurements. The results showed that the reflectance from the abaxial side was 0.05 to 0.10 higher than that of the adaxial side in dicots, while there was no substantial difference between the two sides in monocots. No significant side-related differences in transmittance was observed. Among different combinations of retrieval strategies (from reflectance, from transmittance, from both) the lowest RMSE for chlorophyll was obtained from adaxial reflectance but for carotenoids – from abaxial reflectance data. Observed difference in reflectance may be explained by different surface properties (hairs in the epidermis) or the structure of the mesophyll. We intend to study this further by including these effects in Fluspect and upscaling it to canopy level with the model SCOPE. The project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 721995.