Abstract
The leaf maximum carboxylation rate (Vcmax) is a key parameter in modeling plant photosynthesis. The rapid and accurate acquisition of Vcmax at large scales can improve understanding of global vegetation productivity and the terrestrial carbon cycle. In this article, we assessed the retrieval of Vcmax from satellite data by validating these data using flux observations made at eight crop and grass sites. Firstly, an empirical model applicable to C3 species that was based on the semimechanistic linkage between leaf chlorophyll and Vcmax was used to derive Vcmax from satellite data. Then, using vegetation, soil, and meteorological variables as inputs, the SCOPE model was used to estimate Vcmax from half-hourly or hourly flux observations at each site. The estimates of Vcmax were assessed by comparing the simulated gross primary production (GPP) against the observed GPP: that is, the Vcmax value corresponding to its simulated diurnal GPP data with minimum root-mean-square error (RMSE) was selected as the inverted Vcmax value. Finally, the Vcmax values retrieved from MERIS and Semtinel-3 OLCI satellite data were validated using the in situ flux site observations. The results showed that the estimates of Vcmax based on satellite data successfully captured the seasonal variations in Vcmax retrieved from the tower-based GPP data, giving a mean RMSE value of 15.30 μ mol m−2 s−1. Our results support the retrieval of Vcmax from satellite data based on the link with leaf chlorophyll content and show that there was good agreement between Vcmax derived from remote sensing and flux data.
Highlights
P LANT photosynthesis, a process that converts carbon dioxide into sugars, provides most of the energy needed for lifeManuscript received February 18, 2021; revised April 25, 2021; accepted May 15, 2021
These results indicate that the inverted Cab and leaf area index (LAI) values were within the expected ranges throughout the growing season
Vcmax is a critical physiological parameter used in the modeling of photosynthesis at large scales and requires frequent quantification
Summary
P LANT photosynthesis, a process that converts carbon dioxide into sugars, provides most of the energy needed for lifeManuscript received February 18, 2021; revised April 25, 2021; accepted May 15, 2021. [1]–[3] As this process is a crucial part of the ecosystem carbon cycle, accurate modeling of photosynthesis is necessary [4]. The Farquhar–von Caemmerer–Berry leaf biochemical model [5] embedded in most terrestrial biosphere models is widely used to simulate photosynthesis. This model involves two critical parameters: the leaf maximum carboxylation rate (Vcmax) and the maximum electron transport rate (Jmax) normalized to a reference temperature of 25°C. Vcmax controls CO2 fixation within the carbon reaction process. It is essential to accurately derive Vcmax because of its decisive significance in photosynthesis models
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