Global datasets of leaf photosynthetic capacity for ecological and earth system research
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abstract
Abstract. The maximum rate of Rubisco carboxylation (Vcmax)
determines leaf photosynthetic capacity and is a key parameter for
estimating the terrestrial carbon cycle, but its spatial information is
lacking, hindering global ecological research. Here, we convert leaf
chlorophyll content (LCC) retrieved from satellite data to Vcmax, based
on plants' optimal distribution of nitrogen between light harvesting and
carboxylation pathways. We also derive Vcmax from satellite (GOME-2)
observations of sun-induced chlorophyll fluorescence (SIF) as a proxy of
leaf photosynthesis using a data assimilation technique. These two
independent global Vcmax products agree well (r2=0.79,RMSE=15.46µmol m−2 s−1, P<0.001) and compare well
with 3672 ground-based measurements (r2=0.69,RMSE=13.8µmol m−2 s−1 and P<0.001 for SIF; r2=0.55,RMSE=18.28µmol m−2 s−1 and P<0.001 for LCC). The LCC-derived
Vcmax product is also used to constrain the retrieval of Vcmax from TROPical Ozone Mission (TROPOMI) SIF data to produce an optimized Vcmax product using
both SIF and LCC information. The global distributions of these products are
compatible with Vcmax computed from an ecological optimality theory
using meteorological variables, but importantly reveal additional
information on the influence of land cover, irrigation, soil pH, and leaf
nitrogen on leaf photosynthetic capacity. These satellite-based approaches
and spatial Vcmax products are primed to play a major role in global
ecosystem research. The three remote sensing Vcmax products based on
SIF, LCC, and SIF+LCC are available at https://doi.org/10.5281/zenodo.6466968 (Chen et al., 2022), and the code
for implementing the ecological optimality theory is available at https://github.com/SmithEcophysLab/optimal_vcmax_R and https://doi.org/10.5281/zenodo.5899564 (last access: 31 August 2022) (Smith et al., 2022).
