Find in Library

<p>Terrestrial photosynthesis is the basis for vegetation growth and drives the land carbon cycle. Accurately simulating gross primary production (GPP, ecosystem-level apparent photosynthesis) is key for satellite monitoring and Earth system model predictions under climate change. While robust models exist for describing leaf-level photosynthesis, predictions diverge due to uncertain photosynthetic traits and parameters which vary on multiple spatial and temporal scales. Here, we describe and evaluate a GPP (photosynthesis per unit ground area) model, the P-model, that combines the Farquhar–von Caemmerer–Berry model for <span class="inline-formula">C₃</span> photosynthesis with an optimality principle for the carbon assimilation–transpiration trade-off, and predicts a multi-day average light use efficiency (LUE) for any climate and <span class="inline-formula">C₃</span> vegetation type. The model builds on the theory developed in <span class="cit" id="xref_text.1"><a href="#bib1.bibx139">Prentice et al.</a> (<a href="#bib1.bibx139">2014</a>)</span> and <span class="cit" id="xref_text.2"><a href="#bib1.bibx193">Wang et al.</a> (<a href="#bib1.bibx193">2017</a><a href="#bib1.bibx193">a</a>)</span> and is extended to include low temperature effects on the intrinsic quantum yield and an empirical soil moisture stress factor. The model is forced with site-level data of the fraction of absorbed photosynthetically active radiation (fAPAR) and meteorological data and is evaluated against GPP estimates from a globally distributed network of ecosystem flux measurements. Although the P-model requires relatively few inputs, the <span class="inline-formula"><i>R</i>²</span> for predicted versus observed GPP based on the full model setup is 0.75 (8&thinsp;d mean, 126 sites) – similar to comparable satellite-data-driven GPP models but without predefined vegetation-type-specific parameters. The <span class="inline-formula"><i>R</i>²</span> is reduced to 0.70 when not accounting for the reduction in quantum yield at low temperatures and effects of low soil moisture on LUE. The <span class="inline-formula"><i>R</i>²</span> for the P-model-predicted LUE is 0.32 (means by site) and 0.48 (means by vegetation type). Applying this model for global-scale simulations yields a total global GPP of 106–122&thinsp;Pg&thinsp;C&thinsp;yr<span class="inline-formula">⁻¹</span> (mean of 2001–2011), depending on the fAPAR forcing data. The P-model provides a simple but powerful method for predicting – rather than prescribing – light use efficiency and simulating terrestrial photosynthesis across a wide range of conditions. The model is available as an R package (<i>rpmodel</i>).</p>