Differences in the bacterial community composition and diversity in the decomposition of fallen logs of dominant tree species in the Daxing'anling Mountains

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.