This study aims to explore the impacts of differences in constructive species on soil fungal diversity in cold temperate Larix gmelinii forests, which is expected to provide useful reference for the construction of L. gmelinii forest communities and the maintenance of soil fungal diversity.

The vegetation survey was conducted in the monitoring plot of larch forests in the Greater Khingan Mountains, the important values of L. gmelinii were calculated and used as the experimental treatments. The soil was sequenced by Illumina MiSeq high-throughput sequencing technology to analyze the changes of soil fungal community composition and diversity under the difference of constructive species, and to explore the soil environmental factors affecting its changes.

The soil physical and chemical properties of L. gmelini forests were significantly difference (P < 0.05). The soil AP contents increased significantly with the increase of L. gmelini important value, while soil SOC, MBC, pH and C/N showed a significant downward trend. A total of 463 species of soil fungi belonging to 14 phyla, 47 classes, 96 orders, 176 families and 298 genera were obtained by sequencing. Basidiomycota and Ascomycota were the dominant fungal phyla. Except for Mucoromycota, the relative abundance of other phyla was significantly different (P < 0.05). The dominant genera of larch forests were different, and the relative abundance of each genus was significantly difference (P < 0.05). The results of Chao1, Shannon and Simpson indexes showed that there was no significant difference in the Alpha diversity of soil fungi in L. gmelini forest (P > 0.05). NMDS analysis showed that the Beta diversity of soil fungi was significantly difference (P=0.001). Soil pH, AN, MBC, C/N, SOC, TN, AP and WC were the influencing factors of significant differences in soil fungal community structure. The results of functional prediction showed that the main trophic modes of soil fungi were Symbiotroph, Saprotroph and Saprotroph-Symbiotroph, and Ectomycorrhizal fungi were the most important functional groups. As increase of the important value of L. gmelinii, the Ectomycorrhizal decreased significantly (P < 0.05).

The composition, diversity and potential function of soil fungal community in L. gmelinii forests with different important values of constructive species were significantly different, and the difference of soil physical and chemical properties was the main influencing factor.

This study aimed to explore the changes in the composition, diversity and function of bacterial communities during the decomposition process of different dominant fallen log species in the woodland of the Daxing'an Mountains and investigate the differentiated responses of distribution patterns of major bacterial communities driven by nutrients.

The content of water, pH, TC, TN, cellulose, hemicellulose and lignin in the fallen logs of Betula platyphylla, Pinus sylvestris and Larix gmelini were determined. Illumina MiSeq high-throughput sequencing technology was used to analyze the bacterial composition, relative abundance and ecological functional groups. The relationship between the bacterial community composition of different fallen log species and the nutrient of fallen logs was investigated by redundancy analysis.

In descending order, the bacterial species in the decomposition process of the three fallen logs species were Betula platyphylla, Larix gmelini, and Pinus sylvestris. Among them, the number of unique bacteria in Betula platyphylla was significantly higher than that in Larix gmelini and Pinus sylvestris. The community composition and distribution study showed that Proteobacteria was the absolute dominant phylum in the three fallen log species, and its relative abundance within the group showed significant differences among these fallen log species. Lysinimonas, Sphingomonas and Luteibacter were the dominant genus, and their relative abundance within the group had no significant difference among different fallen log species. The difference analysis of community diversity showed that the difference in fallen log species significantly changed the Alpha diversity within the bacterial communities of Pinus sylvestris and Larix gmelini as well as Pinus sylvestris and Betula platyphylla, which also significantly changed the Beta diversity between groups at the phylum and genus levels. Redundancy analysis showed significant differences in the pH, TC, TN, C/N, hemicellulose and lignin contents among the three fallen log species. Among them, pH, TC, TN, C/N, cellulose and lignin were the key factors affecting the composition and distribution of bacteria at the phylum level, and pH, TN, C/N and cellulose were the key factors at the genus level. The results of bacterial function prediction showed that carbohydrate metabolism and amino acid metabolism were the main functional pathways in the bacteria without fallen log species specificity.

The composition of bacterial communities in different dominant fallen log species showed significant differences in the decomposition process. However, the main bacterial function did not show fallen log species specificity.