© 2004 Heron Publishing—Victoria, Canada
Modeling intra-crown and intra-canopy interactions in red maple: assessment of light transfer on carbon dioxide and water
vapor exchange
William L. Bauerle (1, 2), Joseph D. Bowden (1), Michael F. McLeod (3) and Joe E. Toler (4)
1. Department of Horticulture, Clemson University, Clemson, SC 29634-0319, USA / 2. Corresponding author (bauerle@clemson.edu) / 3. Department of Agricultural and Biological Engineering, Clemson University, Clemson, SC 29634, USA / 4. Department of Applied Economics and Statistics, Clemson University, Clemson, SC 29634, USA / Received June 2, 3003; accepted September 12, 2003; published online March 1, 2004
Summary
Daily and seasonal net photosynthesis (Anet), transpiration (E), absorbed photosynthetically active radiation (Qa) and light-use efficiency (εc) in a red maple container nursery were simulated with MAESTRA, a three-dimensional canopy model. Effects of canopy heterogeneity
were simulated by imposing changes in crown spacing. The light transfer sub-model, a distribution model of incident, direct,
diffuse and scattered radiation within MAESTRA, was validated against field measurements of light interception on an intra-crown
scale. In the container nursery, we found that a fiber-optic-based method of integrating photosynthetically active radiation
(Q) was more suitable for crown-layer light transfer measurements and adjustments than either orthogonal line or individual
quantum sensor measurements. The model underestimated intercepted Q by 9.3, 18 and 11.1% for crown layers 1, 2 and 3, respectively; however, there were linear relationships between model estimates
and observations made with each of the three measurement methods. We used the validated and parameterized light transfer model
to assess intra-crown and intra-canopy light transfer on a layer, crown and canopy basis, and investigated effects of tree
size ratio and tree spacing interactions on Anet, E, Qa and εc in the container nursery. Heterogeneous crown and canopy photosynthesis were predicted to exceed values for a uniform canopy
under space-limiting conditions. Tree size ratio had large effects on Anet, E, Qa and εc when light to lower-canopy layers was limited by inadequate space between crowns. Increasing Qa at lower-crown layers had
the largest impact on whole-crown and whole-canopy Anet, E, Qa and εc. Increases in canopy productivity led to increased water use. Simulations of heterogeneous stands with adequate soil water
indicated that light absorption is maximized under space-limiting conditions as a canopy crown moves toward heterogeneity.
Nursery and plantation productivity per unit land area was optimized by tactical placement of trees of several sizes, but
this was accompanied by increased canopy water use.
Keywords:
light interception, light-use efficiency, modeling.
