PARENT SESSION
Poster Session #12: Modeling.
Tuesday, August 7, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Modelling photosynthesis under different soil temperatures.

CAI, TIEBO¹, DANG*, QING-LAI¹, ¹

ABSTRACT- To examine the effects of soil temperature on a coupled photosynthesis-stomatal conductance model, seedlings of trembling aspen (Populus tremuloides Michx), jack pine (Pinus banksiana Lamb.), black spruce (Picea Mariana (Mill) B.S.P.) and white spruce (Picea glauca (Moench) Voss.) were exposed to 5 °C to 35 °C soil temperatures. Temperature, light and CO₂ response curves of foliar gas exchange were measured four months after the start of the treatment and used for the model parameterization. The effects of soil temperature on four key model parameters, Vcmax (maximum rate of carboxylation), Jmax (maximum rate of electron transport), (efficiency of light energy conversion) and Rd (daytime dark respiration), were modeled using two 3rd-order polynomial equations and a modified Arrhenius equation. Vcmax, Jmax and all increased with soil temperature up to their optimum soil temperatures, and then decreased with further increase in soil temperature, but soil temperature had no effect on Rd. All three equations describe the relationships between soil temperature and model parameters well, but the Arrhenius equation performed best. The four boreal species all showed ecophysiological acclimation to the soil temperature treatments. Two acclimation strategies were identified: (1) Optimization of nitrogen investment between Vcmax and Jmax, and (2) Maintenance of a balance between water use efficiency and nitrogen use efficiency. The modeled relationships between soil temperature and Vcmax, Jmax, and could provide an algorithm for coupling the A-gs model with soil temperature prediction models so that the precision of the A-gs model could be enhanced for large-scale applications where soil temperature changes both spatially and temporally.

KEY WORDS: boreal forest, coupled photosynthesis-stomatal condutance model, gas exchange model, soil temperature