Document: THO-3-33-14

Simultaneous optimization of canopy nitrogen and water use.

BUCKLEY, T.N.* ^1,2, J.M.MILLER ¹ and G.D.FARQUHAR ^1,2

Australian National University, Canberra, ACT, Australia. ¹
Cooperative Research Centre for Greenhouse Accounting, RSBS, ANU, Canberra, ACT, Australia. ²

Abstract:
Nitrogen is optimally distributed in a canopy when the dA/dN is the same for all leaves (A is integrated daily carbon gain and N is nitrogen per unit leaf area). We simultaneously optimized canopy nitrogen allocation and water use with a simulation that combines several recent refinements in canopy modeling. Optimal nitrogen profiles predicted by this model differ from the steep exponential profiles predicted by models that do not account for optimization of water use. For a given total canopy nitrogen content, these optimal profiles are generally less steep and more nearly linear than exponential profiles. These optimal profiles also depend on total canopy nitrogen content and water use, generally becoming less steep with increasing nitrogen and/or water availability. Additionally, the photosynthetic capacity of any given leaf layer in these optimal profiles is not always related to total canopy nitrogen content or water use in a simple fashion. These patterns can be explained in part by variation (with nitrogen or water supply) in the vertical distribution of relative stomatal limitation that emerges when both nitrogen allocation and water use are optimal, and when the canopy model incorporates distinct phases of photosynthesis limitation (carbon fixation and electron transport) and separate integration of sunlit and shaded leaf fractions.

Keywords: optimization, nitrogen, canopy, stomata, lambda

This abstract is being presented at: 11:00 AM in session:
Oral Session #61: Plant Responses to Nutrients.