Does Long-Term Industrial Pollution Affect the Fine and Coarse Root Mass in Forests? Preliminary Investigation of Two Copper Smelter Contaminated Areas

The effect of toxic metals on roots is mainly studied in laboratory single-species experiments. Data for multi-species plant communities obtained in natural conditions are needed to understand ecosystem functioning under pollution. However, information on the industrial emission effects on the below-ground biomass is fragmentary and contradictory. This study aims to analyze the fine and coarse root mass changes along strong pollution gradients. We hypothesize that long-term soil contamination from copper smelter emissions decreases root mass in forests. We assessed the root mass in the forest litter and upper mineral soil layer along two pollution gradients caused by emissions from two copper smelters: in the Middle Urals (coniferous forests) and the Southern Urals (deciduous forests). We divided roots into two diameter fractions (0.5–2.0 mm and 2.1–5.0 mm). Only the fine root mass in the mineral soil in deciduous forests, but not the total root mass, decreased 2.2-fold near the smelter compared to uncontaminated areas. However, this effect is much weaker than for above-ground biomass, and it does not manifest at all in coniferous forests. The percentage of roots localized in the forest litter was negligible (7–10% in the coniferous forests and 2–5% in the deciduous forests) and remained unchanged along the pollution gradients. The absence of a pronounced effect of metal contamination from copper smelter emissions on the fine and coarse root mass may be regarded as evidence of plant communities’ resistance to long-term pollution through a shift in species composition toward tolerant species with high below-ground phytomass, particularly grasses.