Comparing global models of terrestrial net primary productivity (NPP): analysis of differences in light absorption and light‐use efficiency

Abstract

Summary Twelve global net primary productivity (NPP) models were compared: BIOME3, CASA, CARAIB, FBM, GLO‐PEM, HYBRID, KGBM, PLAI, SDBM, SIB2, SILVAN and TURC. These models all use solar radiation as an input, and compute either absorbed solar radiation directly, or the amount of leaves used to absorb solar radiation, represented by the leaf area index (LAI). For all models, we obtained or estimated photosynthetically active radiation absorbed by the canopy (APAR). We then computed the light use efficiency for NPP (LUE) on an annual basis as the ratio of NPP to APAR. We analysed the relative importance for NPP of APAR and LUE. The analyses consider the global values of these factors, their spatial patterns represented by latitudinal variations, and the overall grid cell by grid cell variability. Spatial variability in NPP within a model proved to be determined by APAR, and differences among models by LUE. There was a compensation between APAR and LUE, so that global NPP values fell within the range of ‘generally accepted values’. Overall, APAR was lower for satellite driven models than for the other models. Most computed values of LUE were within the range of published values, except for one model.

Deriving a light use efficiency model from eddy covariance flux data for predicting daily gross primary production across biomes

“…Another very commonly used method for calculating fPAR is based on the Beer-Lambert law (Ruimy et al, 1999):…”

Comparing two approaches for parsimonious vegetation modelling in semiarid regions using satellite data

“…The proportionality between dry matter production and light absorption is known as light use efficiency (LUE), and this relationship has been widely used in vegetation modelling (e.g. Knorr and Heimann, 1995;Ruimy et al, 1999;Running et al, 2000;Running et al, 2004;Montaldo et al, 2005). Stress conditions, such as water or nutrient deficit, tend to diminish LUE value (Green et al, 1985;Li et al, 2008) so that a correction factor has to be applied in these situations.…”

Radiation-use efficiency and the harvest index of winter wheat at different nitrogen levels and their relationships to canopy spectral reflectance

“…During senescence, f APAR is estimated by linear interpolation from 95% of f IPAR at the onset of senescence to zero at maturity. Another approach that is widely used to determine f APAR is based on the LAI and the Beer-Lambert law (Ruimy et al 1999). A third approach to estimate the f APAR is using the canopy NDVI (Verhoef 1984;Myneni and Williams 1994;Goetz et al 1999;Bastiaanssen and Ali 2003).…”

“…f APAR1 was based on the f IPAR according to Lobell et al (2003), and the onset of senescence began from 2 weeks before maturity according to the field observations. f APAR2 was based on f APAR = 0.95 [1 -exp(-k Á LAI)], here k is the light extinction coefficient with a value of 0.5 according to Ruimy et al (1999). f APAR3 was calculated using f APAR = 1.1638NDVI -0.1426, and f APAR4 was according to f APAR = 1.67NDVI -0.08.…”