Variations in C and N Storage and Use Strategies Between White Poplar Ploidy Levels After O₃ Exposure Cessations

Carbon (C) and nitrogen (N) strategies differ across species, and they change in response to environmental stress. There is scarce information about resource storage and remobilization within the same species, especially after stress cessation. We examined the growth of diploid and triploid Populus tomentosa plants during their first year under ambient air or elevated O₃ conditions and the second year after O₃ cessation. Reserves of C and N were labeled at the end of the first year and tracked during the second year to quantify remobilization and reserve use without stress. In the first year without O₃ stress, triploid plants outperformed diploid plants. However, O₃ exposure reduced shoot growth and C reserves in both ploidy levels, and in triploid plants, it also decreased root growth and N reserves. In the second year, plant growth of both ploidy levels was similar, and the growth reduction induced by O₃ exposure was progressively compensated. Triploid plants prioritized new growth and metabolic demands, depleting C and N reserves, and had lower resource acquisition at both O₃ scenarios. Diploid plants prioritized storage but increased C reserve use in response to elevated O₃ only to sustain metabolic demands but not growth. The conservative-acquisitive strategy explains the use of C and N reserves. Our results suggest that diploid plants with a conservative strategy had higher plasticity in C and N reserve use, and they would have a better performance in future climate change scenarios.