Growing season dynamics of net photosynthesis and leaf respiration for a mixed hardwood forest as inferred from flux-variance similarity

Ecosystem-scale estimates of net photosynthesis may be derived from eddy covariance measurements of net ecosystem exchange through the application of flux-variance similarity theory. Net photosynthesis, which is defined as carboxylation minus photorespiration and leaf respiration, differs from gross primary production by the leaf respiration term, which has been implicated as a potential source of error for traditional flux partitioning approaches. Here, we focus on seasonal dynamics of net photosynthesis and leaf respiration by deriving relevant variables (e.g. magnitude of dark respiration, light-saturated rate of net photosynthesis, sensitivity of leaf respiration to light intensity) through rectangular hyperbolic fits of net photosynthesis to photosynthetically active radiation (PAR) throughout the growing season. We find that the magnitude of dark leaf respiration decreases throughout the growing season, while the sensitivity of leaf respiration to light intensity and light-saturated net photosynthesis remain relatively stable. The level of PAR required for carboxylation minus photorespiration to exceed leaf respiration increases over the course of the growing season. We examine how environmental variables, specifically air temperature and volumetric soil moisture, influence these aspects of net photosynthesis. Estimates of leaf-level water use efficiency, a key parameter in the flux-variance similarity theory approach, are evaluated through comparisons with co-located measurements of solar induced fluorescence and sap flux.