Updates to Leaf Respiration Parameterization: Assessing the Impact of Light Inhibition, Leaf Expansion, and a Warming Scenario for Carbon Budget Modeling

Abstract

Understanding the factors that affect leaf respiration is crucial for predicting the balance between respiration and photosynthesis and for modeling carbon budget in general. Many currentday terrestrial biosphere models (TBMs) are based on the biochemical framework presented in Farquhar et al. (1980); however, empirical evidence has shown that these TBMs may be misrepresenting leaf respiration in terms of the sensitivity to environmental factors including light and leaf expansion. Here, the notion that these factors are unimportant for carbon budget modeling is challenged. Additionally, a diurnally asymmetrical warming scenario has been incorporated to assess the impact of a changing climate on model outputs: leaf respiration, growth respiration, above-ground biomass, basal area, leaf area index (LAI), and transpiration. We found that depending on the model output, after about 55 simulation years, light inhibition of leaf respiration led to maximum changes between 12.82–27.48%, the seasonal leaf expansion modification to the model led to maximum changes between 35.86–41.37%, and the warming scenario led to changes between 53.50–90.63%. These results suggest that correctly parameterizing leaf respiration in terms of environmental sensitivities is, in fact, important. In general, lower leaf respiration led to increased growth and higher leaf respiration led to stunted growth. However, in the final 20 years of a simulation with light-induced inhibition of leaf respiration, forest growth decreased relative to the initial model, which had higher leaf respiration. This result, though not intuitive, was explained by light inhibition allowing for the earlier growth of relatively large trees, which have high water requirements and outcompete small trees for limited water resources.