Daily canopy photosynthesis model through temporal and spatial scaling for remote sensing applications

Abstract

Because Farquhar's photosynthesis model is only directly applicable to individual leaves instantaneously, considerable skill is needed to use this model for regional plant growth and carbon budget estimations. In many published models, Farquhar's equations were applied directly to plant canopies by assuming a plant canopy to function like a big-leaf. This big-leaf approximation is found to be acceptable for estimating seasonal trends of canopy photosynthesis but inadequate for simulating its day-to-day variations, when compared with eddy-covariance and gas-exchange chamber measurements from two boreal forests. The daily variation is greatly dampened in big-leaf simulations because the original leaf-level model is partially modified through replacing stomatal conductance with canopy conductance. Alternative approaches such as separating the canopy into sunlit and shaded leaf groups or stratifying the canopy into multiple layers can avoid the problem. Because of non-linear response of leaf photosynthesis to meteorological variables (radiation, temperature and humidity), considerable errors exist in photosynthesis calculation at daily steps without considering the diurnal variability of the variables. To avoid these non-linear effects, we have developed an analytical solution to a simplified daily integral of Farquhar's model by considering the general diurnal patterns of meteorological variables. This daily model not only captures the main effects of diurnal variations on photosynthesis but is also computationally efficient for large area applications. Its application is then not restricted by availability of sub-daily meteorological data. This scheme has been tested using measured CO 2 data from the Boreal Ecosystem-Atmosphere Study (BOREAS), which took place in Manitoba and Saskatchewan in 1994 and1996.

Linking flux network measurements to continental scale simulations: ecosystem carbon dioxide exchange capacity under non-water-stressed conditions

“…Radiation distribution onto sunlit and shaded leaves is described according to Chen et al (1999). The equations for light interception in Chen et al (1999), Eqns (21-24) were based on LAI only.…”

“…Radiation distribution onto sunlit and shaded leaves is described according to Chen et al (1999). The equations for light interception in Chen et al (1999), Eqns (21-24) were based on LAI only. As stems and branches also intercept light, we expanded all occurrences of LAI to plant area index (PAI) with the assumption that the stem area index (SAI) is 14% of the LAI and that PAI 5 SAI1LAI.…”

“…Critical parameters linking observations at flux tower sites with processbased models for estimation of carbon exchange at regional to global scales, including leaf area index (LAI), average carboxylase capacity of the leaves (Vc max ), average leaf light utilization efficiency (alpha), length of the active season for carbon uptake, and sensitivity of stomata to changes in soil water availability can be used to express the potential of an ecosystem to acclimate to changing constraints. While various strategies have been applied to describe spatial and temporal variation in these parameters at large scales (Potter et al, 1993;Running & Hunt, 1993;Bonan, 1995;Sellers et al, 1996;Liu et al, 1997Liu et al, , 1999Chen et al, 1999), consistent or standardized methodologies based on flux network observations have not yet been demonstrated.…”

Retrieval of vegetation clumping index using hot spot signatures measured by POLDER instrument

“…BEPS uses sunlit/shaded leaf separation methodology in the calculations of NPP. With LAI = 4, V = 0.5 (Chen, Liu, Cihlar, & Goulden, 1999), and LAI e = 2, the change in NPP with the V value is tested. We found a decrease in NPP by 19% when V increases from 0.5 to 1.0.…”

Water-carbon coupling modeling of summer maize at the leaf and canopy scales

“…Numerous plant photosynthesis models were also reported, such as the leaf biochemical model suggested by Farquar and Von Caemmerer in 1982, which expresses the photosynthetic rate as a function of intercellular carbon dioxide (CO 2 ) concentration, light quantum flux density, and temperature [8]. And the model is extensively used because of its few parameters [9][10][11]. Canopy-scale photosynthesis models are generally developed by expanding leaf photosynthesis models at the canopy scale, and they can be categorized into single-layer model [12,13], two-layer mod-el [14], and multilayer model [15].…”