A model of the long-term response of carbon allocation and productivity of forests to increased CO2 concentration and nitrogen deposition

The analysis is based on a recent model which predicts that plant light-use efficiency increases with CO₂ but is independent of plant N supply. The results suggest that long-term growth response to CO₂ and N deposition depend strongly on the extent to which stem allocation and foliage allocation are coupled. For both types of coupling, total growth and stem growth increase with increasing N deposition. In the case of linear coupling, however, the N deposition response of stem growth is significantly larger than that of total growth, because of a long-term increase in foliage allocation. The results are compard with those obtained previously from an alternative model of canopy light-use efficiency involving a dependence on the foliar N:C ratio in addition to CO₂.