Fig. 3.

Leaf respiration rate on a weight basis (or: specific respiration rate – SRR) as a function of leaf nitrogen concentration for 22-d-old yellow-poplar leaves of different ages from sapling grown at each of three CO₂ treatments (ambient, and two elevated [CO₂], increased over ambient by 150 and 300 cm³ m⁻³, respectively). Reproduced from Wullschleger et al. (1992) with permission.