Changes in soil available cadmium and bacterial communities after fallowing depend on contamination levels

Purpose Fallowing is an improvement process aimed at promoting the soil health and the sustainability of cultivated land. How it affects the soil health-related abiotic properties and microbial community composition under different levels of cadmium (Cd) contamination is not well known. Materials and methods This study involved applying consistent fallowing practices to paddy soils of low and high Cd content, in order to examine changes in the soil Cd, nutrient, and microbial community using a high-throughput sequencing method. Results and discussion Fallowing significantly decreased available Cd and phosphorus (P) content, but increased ammonium nitrogen (N) on lightly contaminated plots, whereas only P variables changed significantly for heavily contaminated plots. Furthermore, fallowing significantly decreased bacterial Shannon diversity on lightly contaminated plots and altered bacterial community composition on heavily contaminated plots, but it had no impact on archaeal or fungal communities, indicating that bacteria are more sensitive to fallowing than archaea and fungi. Specifically, fallowing significantly promoted some copiotrophic bacteria ( Alphaproteobacteria and Betaproteobacteria ) but suppressed some oligotrophic taxa ( Chloroflexi phylum and OTU5837 belonging to the phylum Acidobacteria ) on highly contaminated plots. Interestingly, the soil microbial community in the lightly contaminated plots was mainly affected by soil pH, C, and N properties, whereas on heavily contaminated plots, it was largely influenced by soil Cd and P variables. Conclusions Overall, these findings showed that fallowing significantly improved soil N availability but decreased Cd availability in lightly contaminated conditions, while shifts in microbial community composition under heavily contaminated conditions may indirectly enhance soil nutrient availability and reduce available Cd. These findings highlight the significance of fallowing to promote the health and the sustainability of Cd-contaminated cultivated land.