COMPENSATION AS A PLANT-RESPONSE TO OZONE AND ASSOCIATED STRESSES - AN ANALYSIS OF ROPIS EXPERIMENTS

This paper examines the role that compensation plays in determining plant response to stress. In addition to exploring the compensatory responses to individual stresses, multiple stresses that induce different compensatory strategies are considered. To do this we have utilized results of many experiments conducted by the Response of Plants to Interacting Stresses (ROPIS) project. Similarities and differences in compensatory responses of plants are considered as a function of growth habits viz. herbaceous annuals, and deciduous and evergreen perennials. The predominant way that plants compensate for stress is through shifts in C allocation, with shifts toward the roots occurring in response to stresses like drought and nutrient deficiencies. Photosynthetic poisons like ozone (O3) and sulfur dioxide (SO2) will induce shifts in favor of the shoot. Plant physiological strategies for coping with stress can also lead to shifts in shoot/root ratio; these include accelerated senescence of injured leaves in favor of production of new foliage, altered leaf area and rates of photosynthesis, and N and C allocation. At the biochemical level, the mechanisms for induction of compensatory shifts are not known; however, it is likely that hormonal changes lead to altered genetic expression of protein synthesis that modify metabolism within tissues or organelles. At the whole plant level, the role of sink strength appears to be important in determining the flow of C and N in stressed plants.