Assessment of Ecosystem Photosynthetic Parameters along Two California Climate Gradients

Abstract

Improving coupled Earth system models of current and future climate requires robust observations that accurately provide parameters and observations for evaluation across spatial scales relevant for the model. Photosynthetic parameters Vcmax and Jmax help to characterize the ability of vegetation to assimilate carbon, a required parameter in most land surface modules of climate models. Remote sensing, flux tower data, and field measurements were collected to develop a methodology to estimate the variability in these parameters across diverse landscapes in Southern California and the Sierras, regions experiencing prolonged drought which is expected to become more common in the future. Vcmax maps were generated with NASA hyperspectral airborne AVIRIS imagery by scaling up leaf level measurements to the canopy and evaluated using flux tower data for nine sites across California. These maps illustrate the expected temporal and spatial changes in the parameter. However, Vcmax estimated from inverse modeling of flux tower data did not fall in the range found in field measurements. The methods developed in this study expand the applicability of imaging spectroscopy in estimating ecosystem metabolism.