Assessing the impact of copper toxicity on soil ecosystems and barley growth: identification of robust indicators

Over the past decade, the escalating prevalence of copper (Cu) pollution in soil has raised significant concerns due to its potential detrimental impacts on soil quality, microbial communities, plant health, food security, and land degradation. Despite extensive research, the response mechanisms, threshold levels, and reliable indicators of Cu pollution remain debated. Therefore, comprehensive studies are needed to gain a better understanding of these dynamics. This study address these gaps by: (1) evaluating Cu toxicity effects on soil biological, biochemical, barley germination, growth, biomass, and physiological parameters, and (2) identifying robust indicators for early assessment of Cu-associated risks. Soil was amended with CuSO₄ at concentrations ranging from 0 to 210 mg kg^-1. Factors exacerbating Cu toxicity included Cu concentration, pH levels, and the duration of Cu accumulation within the soil ecosystem. Consequently, at the highest Cu concentration a significant reduction in soil biological, biochemical, barley germination, growth, biomass, and physiological parameters was observed towards the end of the experiment. Simultaneously, there was a substantial increase in the levels of antioxidant enzymes, malondialdehyde (MDA), reactive oxygen species (ROS), and electrolyte leakage (EL) triggered by Cu presence. Correlation analyses highlighted bacterial populations, microbial biomass carbon (MBC), dehydrogenase activity, respiration rates, pH levels, seedling fresh biomass and height, chlorophyll content, photosynthetic activity, protein content, superoxide dismutase (SOD) activity, ROS levels, and MDA as sensitive indicators of Cu stress. As a result, these parameters are proposed as reliable indicators for predicting Cu toxicity thresholds, excessive accumulation, and associated risks within soil ecosystems. These indicators have implications not only for land degradation but also for food security considerations.