Allocation of Nutrients and Leaf Turnover Rate in Poplar under Ambient and Enriched Ozone Exposure and Soil Nutrient Manipulation.

An excess of ozone (O) is currently stressing plant ecosystems and may negatively affect the nutrient use of plants. Plants may modify leaf turnover rates and nutrient allocation at the organ level to counteract O damage. We investigated leaf turnover rate and allocation of primary (C, N, P, K) and secondary macronutrients (Ca, S, Mg) under various O treatments (ambient concentration, AA, with a daily hourly average of 35 ppb; 1.5 × AA; 2.0 × AA) and fertilization levels (N: 0 and 80 kg N ha y; P: 0 and 80 kg N ha y) in an O-sensitive poplar clone (Oxford: Henry × Dippel) in a Free-Air Controlled Exposure (FACE) experiment. The results indicated that both fertilization and O had a significant impact on the nutrient content. Specifically, fertilization and O increased foliar C and N contents (+5.8% and +34.2%, respectively) and root Ca and Mg contents (+46.3% and +70.2%, respectively). Plants are known to increase the content of certain elements to mitigate the damage caused by high levels of O. The leaf turnover rate was accelerated as a result of increased O exposure, indicating that O plays a main role in influencing this physiological parameter. A PCA result showed that O fumigation affected the overall allocation of primary and secondary elements depending on the organ (leaves, stems, roots). As a conclusion, such different patterns of element allocation in plant leaves in response to elevated O levels can have significant ecological implications.