Effects of leaf trichome and stomata on PAHs uptake in the leaf of winter wheat

To explore the effects of leaf structure on polycyclic aromatic hydrocarbon (PAHs) uptake in winter wheat, an indoor-simulated atmospheric exposure experiment was conducted. The characteristics of trichomes and stomata of leaves of seven winter wheat varieties were compared, and the relationship between leaf structure and PAHs of leaves in winter wheat was analyzed. The results showed that trichome density and length on the leaf abaxial side were larger than those on the adaxial side, while the opposite was true for stomatal density and area for most varieties of winter wheat. Among all wheat varieties, the largest trichome density and length on the leaf abaxial and adaxial side were found in ‘Zhongmai 175’, while the lowest trichome density on the leaf adaxial side was recorded in ‘Changwu 521’. The stomatal density on the leaf adaxial side of ‘Zhongmai 175’ was significantly (P<0.05) higher than that of ‘Cangmai 6005’ ‘Changwu 521’ and ‘Xiaoyan 22’, and the stomatal area on the leaf adaxial side of ‘Changwu 521’ ‘Xiaoyan 22’ and ‘Zhengmai 7698’ were significantly higher than that of ‘Jiaomai 266’. The concentration of Σ₅PAHs in the leaf of ‘Changwu521’ were significantly lower than those of the other six varieties, which may be related to the smaller trichome and stomatal density and shorter trichome in the leaf. At an exposure concentration of 6.00 mg∙L^–1 Σ₅PAHs, PAH concentrations in the leaves decreased with increasing molecular weight of PAHs. In addition, trichome density and length on the leaf adaxial side and phenanthrene (PHE) and Σ₅PAHs concentration showed a significant positive correlation. This result may be due to the higher volatility and lower molecular weight of PHE, which are easily attached to the leaf surface and then absorbed and enriched by leaves. There was a significant correlation between stomatal density on the leaf adaxial side and PHE (P<0.05) and Σ₅PAHs (P<0.05) concentrations, indicating that the denser the stomatal distribution on the leaf adaxial side, the stronger the uptake capacity of PHE. PCA results further confirmed that leaf trichome density was the main limiting factor for PAHs accumulation in leaves. Therefore, selecting winter wheat varieties with a sparse leaf trichome distribution can reduce the human risk of PAHs in winter wheat in polluted areas.