Influence of continuous fertilization on heavy metals accumulation and microorganism communities in greenhouse soils under 22 years of long-term manure organic fertilizer experiment.

This study examined the impact of long-term manure organic fertilizer application (3, 8, 13, 18, and 22 years) on soil physicochemical properties, heavy metal (HM) accumulation, and microbial communities. Long-term manure application markedly elevated nutrient levels such as available N, P and K, and organic matter content in surface and soil profile. Total and DTPA-HM content in different vertical profiles increased with the application time. Fertilization increases the ratio of exchangeable fraction of Cd (2 %-17 %) and Zn (9 %-24 %). The risk assessment of HMs revealed that Cd posed the highest risk (moderate contamination level), followed by Cu, Zn, Pb, and Cr. Due to soil acidification, the time span exceeding the risk screening values of Cr, Cd, and Pb in agricultural land (GB 15618-2018) decreased 53.1, 41.2 and 411.8 years, respectiverly, and for risk intervention values of Cr, Cd, Cu, Pb and Zn, the time reduced to 318.5, 137.0, 71.1, 1029.5 and 19.1 years, respectiverly. Furthermore, manure application altered the composition and structure of the bacteria and fungi community. The abundance of Actinobacteria, Firmicutes, and Ascomycota increased, whereas Proteobacteria, Acidobacteria, and Basidiomycota was inhibited. SEM and RDA indicated that microbial communities were primarily influenced by pH, soil nutrients and HMs.