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 usu ally been conducted with coarse scale models that lump or simplify physiolo gical processes. Foliar respiration (R-d) is a key physiological process in forest ecosystem C cycling; however, there are very few data on leaf respi ration 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 producti on and for parameterizing C cycling models in diverse eastern deciduous har dwood 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) co mmon to the canopy of southern Appalachian forests; and (2) to evaluate the effects of using 'lumped parameter' versus 'species-specific parameter' ap proaches to determining the leaf respiration component of NPP. We used a te mperature-controlled cuvette and an infrared gas analyzer to develop temper ature 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 temperat ures (30 degrees C). Q(10) values ranged from 1.97 to 2.44. Some of the var iation in leaf respiration rates among species was related to differences i n leaf N. Comparison with a lumped parameter model of leaf respiration (PnE T-II) indicated good agreement on average due primarily to combinations of species which resulted in compensating errors; however, there was the poten tial for considerable variation with different mixes of species. (C) 1999 E lsevier Science B.V. All rights reserved.