Inverse Estimation of Parameters for a Coupled Photosynthesis and Stomatal Conductance Model Using Eddy Covariance Measurements at a Black Spruce Forest in Alaska

Abstract:

For better understanding high-latitude carbon and water cycles, parameters of a coupled photosynthesis and stomatal conductance big-leaf model (Farquhar et al., 1980; Ball and Berry, 1987; Baldocchi, 1994) were inversely estimated using gross primary productivity (GPP) and evapotranspiration by eddy covariance measurements at a black spruce forest in interior Alaska (Iwata et al., 2012; Ueyama et al., 2014). We developed a sequential optimization method based on a global optimization technique; shuffled complex evolution (SCE-UA) method (Duan et al., 1993). First, photosynthetic parameters (maximum carboxylation and maximum electron transfer rate at 25^oC; Vc_max25 and J_max25) were optimized for GPP, and then stomatal conductance parameters (m and b in the Ball-Berry model) were optimized for evapotranspiration. Based on our optimization, Vc_max25, J_max25, and m varied seasonally, but b value was almost constant throughout seasons. Vc_max25 and J_max25 were higher in summer months than other months, which related to understory leaf area index. m was higher in winter months than other months, but did not significantly change throughout the growing season. Our results indicated that simulations using constant ecophysiological parameters could underestimate photosynthesis and evapotranspiration of high-latitude ecosystems.

References

Ball and Berry, 1987: Progress in Photosynthesis Research, pp 221-224.

Baldocchi, 1994: Tree Physiol., 14, 1069-1079.

Duan et al., 1993: J. Optimization Theory and Applications, 76, 501-521.

Farquhar et al., 1980: Planta, 149, 78-90.

Iwata et al., 2012: Agric. For. Meteorol., 161, 107-115.

Ueyama et al., 2014: Global Change Biol., 20, 1161-1173.