Effects of soil temperature on parameters of a coupled photosynthesis-stomatal conductance model

To axamine 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 soil temperatures ranging from 5 to 35 degreesC for 4 months. Light and CO2 response curves of foliar gas exchange were measured for model parameterization. The effects of soil temperature on four key model parameters, V-cmax (maximum rate of carboxylation), J(max). (maximum rate of electron transport), alpha (energy conversion efficiency or quantum efficiency of electron transport) and R-d (daytime dark respiration), were modeled using two third-order polynomial equations and a modified Arrhenius equation. In all species, V-cmax and J(max) increased with soil temperature up to an optimum, and then decreased with further increases in soil temperature. In the conifers, alpha showed a similar response to soil temperature as V-cmax and J(max), but soil temperature had no significant effect on alpha in aspen. Soil temperature had no significant effect on Rd in any species. The three equations described the relationships between soil temperature and the model parameters reasonably well, but performed best for V-cmax and worst for alpha. No significant relationships were identified between soil temperature and the parameters of the stomatal conductance model.