Integrating the effects of simultaneous multiple stresses on plants using the simulation model TREGRO

TREGRO, a model of tree physiological response to environmental stress, was developed to examine the details of tree response to the interaction between ozone stress and nutrient deficiency. TREGRO was used to test the hypothesis that the nutrient deficiency would exacerbate growth reductions caused by ozone. When TREGRO was applied to a range of multiple-stress scenarios involving these two stresses, the simulated effects of the combined stresses in reducing red spruce (Picea rubens Sarg.) tree growth were less than the sum of the effects simulated when each stress was acting alone. Red spruce, a species with a growth strategy involving low maximum potential growth rates and storage in C reserves, showed simulated patterns of allocation that minimized the added effect of ozone when Mg nutrient availability was low. In contrast, ponderosa pine (Pinus ponderosa Dougl.), a species that allocated C to the construction of new tissue preferentially, showed little ability to ameliorate ozone stress under low nutrient conditions. In neither case were the effects of ozone increased by nutrient deficiency. It is speculated that a species which maintains maximum C demand rates considerably below rates of C supply may be better able to adjust to conditions of multiple stresses.