GEOSCAN Search Results: Fastlink


TitleDaily Canopy Photosynthesis Model Through Temporal and Spatial Scaling for Remote Sensing Applications
AuthorChen, J M; Liu, J; Cihlar, J; Goulden, M L
SourceEcological Modelling; 124, 2, 1999 p. 99-119
Alt SeriesEarth Sciences Sector, Contribution Series 20042572
AbstractBecause Farquhar's photosynthesis model was developed and tested at leaf level and is only directly applicable to individual leaves instantaneously, considerable skill is needed to use this model for regional 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 suitable 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. The 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 measures CO2 data from the BOReal Ecosystem-Atmosphere Study (BOREAS), which took place in Manitoba and Saskatchewan in 1994 and 1996.

Date modified: