Oxidative Stress Assessment in Poplar and Willow Clones on Landfills and Their Relation to Physiological Response Parameters

Biochemical markers of oxidative stress were used to evaluate the responses of poplar and willow clones grown in phytoremediation buffer plantations on landfill sites in Novi Sad and Vinča (near Belgrade), Serbia. The experiment was conducted using a randomized block design with three replications, each comprising blocks of nine plants arranged in a 3 × 3 layout, with ten leaves collected per block. Key parameters assessed included total phenolic content (TPC), total flavonoid content (TFC), ferric-reducing antioxidant power (FRAP), radical scavenging activity of DPPH (DPPH), and ABTS radical scavenging activity (ABTS). For the parameters FRAP, DPPH, and ABTS, higher values were recorded at the Novi Sad site, likely due to plants’ continuous groundwater access. The results indicate significant clone × site interaction for TPC, suggesting environment-specific clone responses for this parameter. There was a significant effect of clone on the variation in TPC, TFC, and FRAP, evidenced by the clear distinction in these parameters between poplar and willow clones, as poplar clones achieved higher values than willow clones. No significant effect of any of the examined sources of variation was found for the TFC/TPC ratio or FPR, and Pannonia was found to achieve significantly higher values compared to willow and clone 135/81. According to principal component analysis, the examined biochemical parameters were divided into three groups. Considering the results from the previous study of physiological and biomass parameters, DPPH and ABTS were included in the first group along with stomatal conductance (g s ), transpiration (E), and total biomass of the above-ground part (m P ), while TPC, TFC, and FRAP comprised the second group and FPR the third group. The first two principal components accounted for most of the variability, with the first PC clearly separating the interaction treatments of poplar and willow clones, and the second PC further distinguishing the treatments according to site. These findings underscore the difference between parameters regarding the effect of site and differences between clones. Further study of the significance of these parameters in selecting appropriate clones for phytoremediation on landfills, as well as on contaminated lands in general, is recommended.