Leaf Respiration in Terrestrial Biosphere Models

Abstract

How leaf respiration (Rd) is represented in leading terrestrial biosphere models (TBMsTerrestrial biomass models (TBMs)) is reviewed, followed by an overview of how emerging global datasets provide opportunities to improve parameterization of leaf Rd in large-scale models. We first outline how TBMs have historically accounted for variations in respiratory CO2 release in mature leaves, using assumed relationships between leaf nitrogen, photosynthetic capacity and Rd. The need for TBMs to account for light inhibition of Rd in mature leaves is highlighted, followed by a discussion on how Rd of upper canopyCanopyleaves is used to predict maintenanceMaintenancerespirationMaintenance respirationin whole plants. We then outline how respiratory energy requirements of growth are accounted for in TBMs, pointing out that current assumptions on the costs of biosynthesis are based on theoretical calculations that may not be valid for all plant species and environments. The chapter then considers how improvements might be made to TBMs with respect to the parameterization of leaf Rd. We show how recently compiled datasets provide improved capacity to predict global variations in baseline Rd measured at a standard temperature, and how baseline Rd likely acclimates to sustained changes in growth temperature. Application of this dataset reveals markedly higher rates of leaf Rd than currently predicted by TBMsTerrestrial biomass models (TBMs), suggesting that TBMs may be underestimating global plant respiratory CO2 release. The availability of a new, global dataset on short-term temperature responses of leaf Rd is highlighted. Analysis of this dataset reveals that leaf Rd does not exhibit the exponential response assumed by most TBMs; rather, the temperature-sensitivity declines as leaves warm, with convergence in the temperature-response across biomesBiomeand plant functional typesPlant functional type (PFT). We show how equations derived from these datasets may provide the TBM community with a new framework to improve representation of mature leaf respiration in TBMs.