Global datasets of leaf photosynthetic capacity for ecological and earth system research

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).

Why models underestimate West African tropical forest productivity

“…The high photosynthetic capacity in semi-arid forest or savanna is consistent with other field studies in West Africa ( 49 ). V cmax inferred from remotely sensed leaf chlorophyll data and V cmax predicted by the P model both show exceptionally high values in West Africa and parts of India – substantially higher than in Amazonia or SE Asia ( 58 , 59 ). These seasonal forests on more fertile soils may have photosynthesis rates optimized to high light, temperature and VPD (also see field study ( 60 )).…”

“…Vcmax predicted by the P model both show exceptionally high values in West Africa and parts of Indiasubstantially higher than in Amazonia or SE Asia (58,59). These seasonal forests on more fertile soils may have photosynthesis rates optimized to high light, temperature and VPD (also see field study (60)).…”

Water level drawdown makes boreal peatland vegetation more responsive to weather conditions

“…Deeper WT improves the habitat conditions for most vascular plants and increases their diversity and biomass (Zeng et al, 2021), as well as it also increases their capacity to respond to warmer temperatures (McPartland et al, 2019; Weltzing et al, 2000). In addition, long‐term WLD changes the plant community composition (Kokkonen et al, 2019), and this in turn will affect the productivity of the ecosystem as PFTs vary in their photosynthetic capacity (Chen et al, 2022; He et al, 2019), but also in their ability to respond and take advantage of increasing temperatures, with graminoids showing particularly clear responses (Riutta et al, 2007). Similarly, in our study the growth of graminoids clearly increased at all WLD sites during the warmer growing season in 2021.…”

Widespread and complex drought effects on vegetation physiology inferred from space

“…On the other hand, vegetation physiology, such as maximum carboxylation rate and stomatal conductance, have so far only been directly assessed at the site level 9 . At the same time, their changes are only implicitly included in global observations 10 . Vegetation physiology typically responds faster than the vegetation structure to environmental stressors at the ecosystem scale, yet the drought response is commonly diagnosed by concurrent structural changes which could lead to an underestimation of the vegetation functional responses 8 , 11 – 13 .…”

“…Recent advances in satellite remote sensing 10 , 17 – 22 bring new opportunities to monitor vegetation physiology and resulting functioning as illustrated in Fig. 1 .…”