Evaluation and improvement of model algorithms for predicting belowground carbon allocation in forests

Abstract

Rapidly rising concentrations of atmospheric carbon dioxide (CO ₂) influence forest productivity by stimulating plant growth. It can also modify carbon partitioning patterns, altering the global carbon cycle. Nitrogen and carbon cycles are tightly linked; with changes in nitrogen availability affecting ecosystem carbon allocation by shifting carbon to roots for nitrogen uptake. This paper discusses a modification to the PnET-CN model (Aber et al. 1997) developed to shift plant carbon allocation belowground in response to nitrogen limitation. According to functional equilibrium models of plant carbon allocation, a nitrogen control mechanism alters belowground carbon estimates by increasing carbon allocation to fine roots when nitrogen resources are low. Testing of the modified mechanism with data from three free-air CO ₂ enrichment (FACE) forests supported the mechanism by allocating more carbon to fine roots. Application of the model with data from five northeastern forests, under a variety of global climate change scenarios, also supported the modified mechanism with an increase in soil carbon storage.