Optimal co-allocation of carbon and nitrogen in a forest stand at steady state
Article first published online: 10 JUL 2008
© The Authors (2008). Journal compilation © New Phytologist (2008)
Volume 180, Issue 1, pages 114–123, October 2008
How to Cite
Mäkelä, A., Valentine, H. T. and Helmisaari, H.-S. (2008), Optimal co-allocation of carbon and nitrogen in a forest stand at steady state. New Phytologist, 180: 114–123. doi: 10.1111/j.1469-8137.2008.02558.x
- Issue published online: 2 SEP 2008
- Article first published online: 10 JUL 2008
- Received: 14 May 2008Accepted: 19 May 2008
- carbon and nitrogen;
- functional balance;
- growth model;
- productivity and biomass;
- steady state
- • Nitrogen (N) is essential for plant production, but N uptake imposes carbon (C) costs through maintenance respiration and fine-root construction, suggesting that an optimal C:N balance can be found. Previous studies have elaborated this optimum under exponential growth; work on closed canopies has focused on foliage only. Here, the optimal co-allocation of C and N to foliage, fine roots and live wood is examined in a closed forest stand.
- • Optimal co-allocation maximizes net primary productivity (NPP) as constrained by stand-level C and N balances and the pipe model. Photosynthesis and maintenance respiration increase with foliar nitrogen concentration ([N]), and stand-level photosynthesis and N uptake saturate at high foliage and fine-root density.
- • Optimal NPP increases almost linearly from low to moderate N availability, saturating at high N. Where N availability is very low or very high, the system resembles a functional balance with a steady foliage [N]; in between, [N] increases with N availability. Carbon allocation to fine roots decreases, allocation to wood increases, and allocation to foliage remains stable with increasing N availability.
- • The predicted relationships between biomass density and foliage [N] are in reasonable agreement with data from coniferous stands across Finland. All predictions agree with our qualitative understanding of N effects on growth.