Fungal community composition change and heavy metal accumulation in response to the long-term application of anaerobically digested slurry in a paddy soil

Anaerobically digested slurry (ADS) has been widely used as a liquid fertilizer in agroecosystems. However, there is scant information on the effects of successive ADS applications on heavy metals (HMs) accumulation and fungal community composition in paddy soils. In this study, we conducted a field experiment over 10 years to assess the changes in soil HMs and fungal community composition under the long-term application of ADS in a paddy field. The four treatments were (1) no fertilizer (CK); (2) mineral fertilizer and 270 kg N ha(-1) from urea (MF); (3) 270 kg N ha(-1) from ADS (ADS1); and (4) 540 kg N ha(-1) from ADS (ADS2). The results revealed that ADS application improved paddy soil fertility compared to that under the MF treatment by increasing soil organic C (SOC), total N (TN) and available potassium (AK). Long-term application of ADS significantly increased soil total and available Zn (TZn and AZn) concentrations as compared to those under the MF treatment. However, there were no significant differences in the total and available Cu concentrations or the total Pb concentration between the ADS and MF treatments. Sequence analysis showed that application of ADS increased the fungal richness indexes (Chao1 and ACE) compared to MF treatment. Principal coordinate analysis (PCoA) showed that the soil fungal community compositions were significantly separated by high levels of ADS application. Long-term application of ADS increased the relative abundance of classes Sordariomycetes, Dothideomycetes and Agaricomycetes by 20.8-29.0%, 107.3-141.4% and 289.5-387.5%, respectively, but decreased that of Pezizomycetes by 14.0-33.0% compared to that under the MF treatment. At the genus level, compared to those under the MF treatment, the relative abundances of Pyrenochaetopsis and Myrothecium were significantly increased by the application of ADS, but those of Mrakia and Tetracladium were significantly decreased. Redundancy analysis (RDA) revealed that SOC, AZn and AP were the three most important factors affecting the fungal community composition of the paddy soil. Our findings suggested that fungal community composition could be affected by changes in the chemical properties and heavy metal contents of paddy soil under high application of ADS in the long term.