Primary production over land.

Gross primary production (GPP) is the basis for life on Earth. Terrestrial net primary production (NPP) is the remainder after plant (autotrophic) respiration (RA) has returned approximately half of the terrestrial GPP to the atmosphere, in the process of carrying out essential functions (metabolism and growth). Most of the NPP is used to construct plant tissues, although there are some losses via the emission of volatile organic compounds (VOCs) to the atmosphere and the exudation of labile organic compounds to the rhizosphere.The objective of the TerrA-P project is to define, implement and validate a model to derive information on primary production by vegetation based on data from MERIS and Sentinel-3. The project combines the expertise from three domains: the ecophysiology of plants as expressed in the productivity model, the EO data sets that can be used as input for this model, and the in-situ data that allow validation of the model outcome using EO-input data.The P-model developed by Imperial College London (Wang, H., I.C. Prentice, et al. (2016); http://dx.doi.org/10.1101/040246) will be used as a basis for the estimation of GPP. This model starts from first principles, has a firm basis in theory and provides the optimum combination of parsimony, theoretical foundation, and empirical support. It is based on the standard (Farquhar, von Caemmerer and Berry) photosynthesis model while also accounting for acclimation processes that lead to a proportional relationship between GPP and light absorbed, the constant or proportionality varying as a function of environmental variables (temperature, vapour pressure deficit, atmospheric pressure and CO2). The model has been tested using eddy covariance GPP data derived from flux sites worldwide. This model will be further elaborated to use EO data (fAPAR) derived from Sentinel-3, to include estimated uncertainties at the pixel level, to comply with the current user requirements of such products, and to provide estimates of above-ground biomass production (ABP) as well as GPP. The model will be validated using data from many flux measurement sites worldwide, and will be benchmarked against other comparable products.

Keywords:ECOSYSTEMS

Disciplines:Ecology, Environmental science and management, Other environmental sciences