Di-(2-ethylhexyl) phthalate (DEHP) contamination suppressed soil microbial biomass carbon and mitigated CO emissions against the background of alfalfa from different soils.

Plastic mulching and organic amendments are prevalent agricultural practices worldwide. Plastic mulching has long been suspected as a significant source of DEHP contamination in terrestrial ecosystems. However, effects of DEHP contamination on greenhouse gas emissions and microbial biomass carbon (MBC) remain unclear. Here, a microcosm experiment was set up to assess the impact of DEHP exposure on MBC and carbon dioxide (CO) emission in two different soils (acidic and alkaline) with the inclusion of alfalfa straw. The treatment includes: (i) control with no amendment (T); (ii) alfalfa straw addition (20 g kg) (T); (iii) DEHP (10 mg kg) + alfalfa straw (T); and (iv) DEHP (100 mg kg) + alfalfa straw (T). Against the background of alfalfa inclusion, DEHP exposure led to a potential reduction in cumulative CO emissions by 16.35 % and 6.91 % in alkaline soil and 12.27 % and 13.65 % in acidic soil for T and T, respectively. The addition of DEHP triggered CO emissions and manifested a detrimental negative priming effect in both soil types. In both soils, average CO emission fluxes were highest for the T treatment. The MBC fluctuated at around 80 mg kg for the control group, alfalfa straw alone (T) treatment considerably enhanced MBC contents, whereas DEHP contamination in T and T treatments suppressed the stimulatory effect of alfalfa on MBC in both alkaline and acidic soils. Furthermore, a positive relationship was observed between soil CO emissions and MBC in both soils. Overall, these findings highlight the toxic impact of DEHP on MBC and its role in mitigating CO emissions in diverse soils. DEHP exposure counters the CO emissions induced by alfalfa straw. In addition, the inhibitory effect of DEHP on CO fluxes in alkaline soil is less pronounced than in acidic soil. Therefore, further cutting-edge research is crucial since DEHP contamination poses serious ecological threats to agroecosystems.