Soil water depletion induces discrepancies between in situ measured vegetation indices and photosynthesis in a temperate heathland

Vegetation indices (VIs) derived from optical sensors have been used as proxies for monitoring gross primary productivity (GPP). In contrast to satellite-based VI’s, in situ derived VI’s exhibit very high temporal resolution. This high resolution implies much larger sample sizes to test the performance of VI’s using eddy covariance-based in situ GPP estimates. Here, we test the potential of in situ derived VI’s to estimate GPP in a temperate heathland ecosystem. To this end, we used CO2 fluxes obtained with the eddy covariance technique and a multi-spectral sensors to calculate several greenness-, structure- and chlorophyll-sensitive VI’s (e.g. the Terrestrial Chlorophyll Index and the Inverted Red-Edge Chlorophyll Index) as proxies of GPP. Results indicated that vegetation indices differed in capturing the temporal variability of GPP, but all failed during an extreme drought period. After integrating a drought indicator (e.g. soil moisture content, aridity index, and potential/actual evapotranspiration ratio) in the regression model, the VI’s performances drastically improved. Among all tested indices, IRECI and TCI came out as the most promising VI’s capturing best the temporal variation in GPP (R2 = 0.73 and RMSE = 1.85, and R2 = 0.77, RMSE = 1.69), providing that drought stress is properly accounted for. Our findings have implications for the development and improvement of global ecological models for drought monitoring based on proximal and remote sensing data.

MALEKI Maral;  ARRIGA Nicola;  ROLAND Marilyn;  WIENEKE Sebastian;  BARRIOS José Miguel;  VAN HOOLST Roel;  PENUELAS J.;  JANSSENS Ivan A.;  BALZAROLO Manuela; 

2022-08-17

ELSEVIER

JRC126655

0168-1923 (online),   

https://www.sciencedirect.com/science/article/pii/S0168192322002970?via%3Dihub,    https://publications.jrc.ec.europa.eu/repository/handle/JRC126655,   

10.1016/j.agrformet.2022.109110 (online),