Challenges to modelling NPP in diverse eastern deciduous forests: Species-level comparisons of foliar respiration responses to temperature and nitrogen

Modelling net primary production (NPP) in eastern deciduous forests has usually been conducted with coarse scale models that lump or simplify physiological processes. Foliar respiration (R(d)) is a key physiological process in forest ecosystem C cycling; however, there are very few data on leaf respiration (R(d)) for deciduous hardwood species. As a result, leaf R(d) is one of the most superficially treated processes in NPP models. We hypothesize that these data are critical for understanding patterns of net primary production and for parameterizing C cycling models in diverse eastern deciduous hardwood forests. Our objectives were: (1) to determine differences in leaf R(d) for seven hardwood species (Acer rubrum, Liriodendron tulipifera, Quercus alba, Quercus coccinea, Quercus rubra, Quercus prinus and Carya glabra) common to the canopy of southern Appalachian forests; and (2) to evaluate the effects of using 'lumped parameter' versus 'species-specific parameter' approaches to determining the leaf respiration component of NPP. We used a temperature-controlled cuvette and an infrared gas analyzer to develop temperature response curves during the night (24:00-06:00 h). Differences in leaf respiration rates (expressed on either a mass or area basis) among species were substantial, varying by greater than three-fold at high leaf temperatures (30°C). Q₁₀ values ranged from 1.97 to 2.44. Some of the variation in leaf respiration rates among species was related to differences in leaf N. Comparison with a lumped parameter model of leaf respiration (PnET-II) indicated good agreement on average due primarily to combinations of species which resulted in compensating errors; however, there was the potential for considerable variation with different mixes of species.