Mi-Seq sequencing analysis
For fungi, a total of 415,816 sequences were obtained from the rhizosphere soil samples after undergoing Illumina Mi-Seq sequencing for the ITS1 region of ITS rDNA. Their average length was 228 bp. From the non-rhizosphere soil samples, a total of 408,590 sequences were generated, having an average length of 230 bp.
For bacteria, 426,303 sequences in all were obtained from the non-rhizosphere soil samples after their Illumina Mi-Seq sequencing of the 16S rDNA V3–V4 region; these had an average length of 416 bp. From the rhizosphere soil samples, 363,833 sequences were generated overall, with an average length of 416 bp.
Microbial community composition
Two taxonomic strata, phylum and genus, were used to examine similarities and differences in the microbial communities under the two mulching film treatments.
Both treatments exhibited a similar dominant fungal community at the level of phylum dwelling in the rhizosphere and non-rhizosphere soils. The Ascomycota, Basidiomycota, and Mortierellomycota were the most dominant phyla. However, differences emerged at the genus level in the rhizosphere and non-rhizosphere soil between the two treatments (Fig. 1a, b).
The dominant fungal genera in the rhizosphere soil of PEBOS were Pseudeurotium (24.4%), Preussia (18.9%), and Cladosporium (13.4%), whereas Metarhizium (17.7%) in rhizosphere soil was higher in the DPBOS than PEBOS treatment (4.0%). The dominant genera present in the non-rhizosphere soil of DPBOS were Pseudeurotium (22.7%), Vishniacozyma (13.3%), and Cladosporium (10.8%). Under the PEBOS treatment, the most dominant genus was Pseudeurotium (28.3%), followed by Cladosporium (14.1%) and Vishniacozyma (12.7%) (Fig. 1c, d).
The Proteobacteria, Actinobacteriota, Chloroflexi, and Acidobacteriota were the most dominant bacterial phyla between the two treatments in the rhizosphere and non-rhizosphere soil samples (Fig. 2a, b).
The most abundance bacterial genera in the rhizosphere soil of PEBOS were norank_f_Gemmatimonadaceae (3.3%). Similarly, the most abundant bacterial genera in the DPBOS treatment were same to the PEBOS treatment. In stark contrast, evidently the non-rhizosphere soil harbored distinctive dominant taxa (Fig. 2c, d). The most abundance bacterial genera in the non-rhizosphere soil of PEBOS were norank_f_norank_o_Vicinamibacterales (3.6%), and those of the DPBOS treatment were also norank_f_norank_o_Vicinamibacterales (3.8%). The abundance of Bacillus was higher in PEBOS than DPBOS in both rhizosphere and non-rhizosphere soil. For Streptomyces, the abundance in DPBOS is higher than PEBOS in non-rhizosphere soil.
Microbial α-diversity
Five indexes—Sobs, Shannon, Simpson, Ace, and Chao were used to convey the diversity and richness under each of the two mulching treatments. For non-rhizosphere soil, the Sobs, Shannon, Ace, and Chao values for the fungal community differed significantly between the DPBOS and PEBOS treatments, indicated that the diversity and richness of non-rhizosphere soil fungal was altered considerably by the type of mulching film applied to grow cotton plants (Fig. 3). For rhizosphere soil’s fungal community, no significant differences were discernible between the DPBOS and PEBOS treatments.
Moreover, no significant difference was detected in the bacterial community between DPBOS and PEBOS treatments in either the rhizosphere and non-rhizosphere soils. This indicated that application of the PE mulching film negligibly influences the bacterial diversity and richness when compared with using degradable or PBAT mulching film, either in rhizosphere or non-rhizosphere soils.
Microbial β-diversity
PCoA was used to infer divergence in microbial community structure between treatments. According to the PCoA results, the bacterial community under the DPBOS treatment was separated from PEBOS treatment, in both the rhizosphere and non-rhizosphere soil zones, which indicated that bacterial community structure was significantly altered by the type of mulching film used (Fig. 4a, b). The fungal community showed a similar response to the DPBOS treatment versus PEBOS treatment as the bacterial community. That is, the fungal community structure in DPBOS treatment was likewise separated from PEBOS treatment in both rhizosphere and non-rhizosphere soil, suggesting that fungal community structure was remarkably affected by the application of different mulching films (Fig. 4c, d).