Objective Poplar leaves and fine roots play a key role in the carbon and nutrient cycle (such as nitrogen and phosphorus) in the forest ecosystem. However, the response of fine roots to ozone (O3) stress has been poorly studied, and the difference in responses of leaves and fine roots to O3 is still unclear. This study thus aimed to clarify the difference in responses to O3 dose of leaves and fine roots, two rapidly decomposing organs, and to provide reference for understanding the response mechanism of poplar to O3 pollution from the perspective of aboveground and belowground feedback.
Method Five O3 concentration levels were set with the open-top chambers to explore whether the functional traits of poplar leaves and fine roots respond differently to O3 dose.
Result There was significant hormesis on the response of tannin content of leaves and P content of fine roots to O3 stress, which showed a positive effect before toxicological O3 threshold and a negative effect after toxicological O3 threshold. Leaf saturated photosynthetic rate, fine root biomass and soluble sugar content of leaves and fine roots showed a toxicological O3 threshold, but not significant hormesis. Water use efficiency and the biomass of leaves, stems, coarse roots and total roots decreased linearly with O3 dose increasing. The ratio of fine roots to leaves in the content of C, N, soluble sugar, lignin, and lignin∶N did not change with O3 dose increasing. The ratio of fine roots to leaves in the content of P, starch, and TNC increased with the O3 dose increasing, while tannin content first declined and then rose with O3 dose increasing (O3 threshold value of 37.25 μmol/mol·h).
Conclusion These results indicate that the significant differences in the responses of leaves and fine roots to O3 pollution will result in marked changes in the relative belowground roles of these two litter sources within poplar plantations. O3 stress could induce more P and non-structural carbohydrates to fine roots for storage relative to leaves, which might be a coping strategy for poplar exposed to O3 stress.