Poplar root anatomy after exposure to elevated O3 in combination with nitrogen and phosphorus

Key message Elevated O-3, particularly in interaction with N and/or P levels, induced tissue- and cell type-specific changes in the anatomical structure of poplar roots. Ozone (O-3) sensitive poplar clone Populus maximowiczii Henry x berolinensis Dippel was subjected to two levels of O-3 (ambient and 2 x ambient) in combination with two levels of nitrogen (N) (0 and 80 kg ha(-1)) and three levels of phosphorus (P) (0, 40 and 80 kg ha(-1)) in an open-air pot experiment. Effects of O-3 in combination with N and P on anatomical structure of xylem, bark and primary tissues and consequences for theoretical hydraulic properties were investigated after one growing season in 2-mm roots under the microscope. Effect of O-3 as single factor was observed as increased primary xylem area and number of protoxylem poles, increased secondary xylem area and accumulated potential hydraulic conductivity. Vessel density, but not vessel size was negatively affected by O-3. Stronger correlation between tangential vessel diameter and vessel density was encountered under ambient O-3, indicating a slight dysregulation of vessel formation under elevated O-3. Increasing P resulted in increased number of protoxylem poles, while N mostly acted in interaction with O-3 or P. There was a strong interaction between O-3 x N x P on vessel grouping index and mean vessel group size. At elevated O-3, effects of both nutrients on vessel grouping and mean vessel group size were repressed. Under ambient O-3, application of N resulted in increased fibre cell thickness, which was not the case under elevated O-3, indicating carbon-saving mechanisms.

Automated summary

Elevated O-3, particularly in interaction with N and/or P levels, induced tissue- and cell type-specific changes in the anatomical structure of poplar roots. The effects of O-3 in combination with N and P on anatomical structure and hydraulic properties were investigated, revealing complex interactions between these factors. Elevated O-3 suppressed the effects of N and P on vessel grouping and size, indicating a need for further research on carbon-saving mechanisms in response to environmental stressors.