Effects of Plant Growth Characteristics on Biogeochemistry and Community Composition in a Changing Climate

ABSTRACT

Vegetation growth characteristics influence ecosystem biogeochemistry and must be incorporated in models used to project biogeochemical responses to climate variations. We used a multiple-element limitation model (MEL) to examine how variations in nutrient use efficiency (NUE) and net primary production to biomass ratio (nPBR) affect changes in ecosystem C stocks after an increase in temperature and atmospheric CO₂. nPBR influences the initial rates of response, but the magnitude and direction of long-term responses are determined by NUE. MEL was used to simulate responses to climate change in communities composed of two species differing in nPBR and/or NUE. When only nPBR differed between the species, the high-nPBR species outgrew the low-nPBR species early in the simulations, but the shift in dominance was transitory because of secondary N limitations. High-NUE species were less affected by secondary N limitations and were therefore favored under elevated CO₂. Increased temperature stimulated N release from soil organic matter (SOM) and therefore favored low-NUE species. The combined release from C and N limitation under the combination of increased temperature and elevated CO₂ favored high-NUE species. High C:N litter from high-NUE species limited the N-supply rate from SOM, which favors the dominance of the high-NUE species in the short term. However, in the long term increased litter production resulted in SOM accumulation, which reestablished a N supply rate favorable to the reestablishment and dominance of the low-NUE species. Conditions then reverted to a state favorable to the high-NUE species.