1. Forest succession is a key driver of plant communities and understanding succession is central to forest restoration. Currently, the information on the response of the microbial community to the forest succession process, however, is limited. In the present study, we investigated the dynamics of the soil bacterial community in three forest types undergoing succession caused by pine wilt disease, representing the initial pine forest, gradual mixed pine and broadleaved forest, and eventual broadleaved forest, using Illumina MiSeq coupled with Functional Annotation of Prokaryotic Taxa (FAPROTAX) analysis. 2. The results showed that the soil pH, contents of soil organic carbon (SOC) and soil total nitrogen (TN) increased after the occurrence of initial succession and differed among the forest sites. The mixed pine forest had significantly higher bacteria biomass (p < 0.05), whereas, the total microbial biomass did not differ during the succession. The bacterial community diversity and richness increased significantly following the succession process (p < 0.05). Proteobacteria, Actinobacteria, Acidobacteria and Bacteroidetes were the dominant phyla across the succession, in which the abundance of Bacteroidetes significantly increased (p < 0.05), whereas, Planctomycetes, WPS-2 and Burkholder decreased in abundance after succession occurred (p < 0.05). 3. The three forests formed distinct bacterial community structures during the succession (p < 0.05), whereas, only two functional structures were clustered, in which the mixed and pure broadleaved forest did not differ. The dominant functional groups involved in the C cycle in the initial pure pine forest were replaced gradually by the groups involved in N and S cycles following the subsequent succession. The soil pH, soil TN and SOC were the most important factors affecting the bacterial community and functional structures during the succession. 4. These results indicate that the bacterial community and function shift drastically in the early stages of succession, which reflects the changes in ecological environment caused by succession. The findings provide useful information to better understand the response of microbes to natural forest disturbance and highlight the importance of microbes during forest succession. | 2549 Functional Ecology QU et al.

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Pine wilt disease (PWD) caused by the nematode Bursaphelenchus xylophilus is a devastating disease in conifer forests in Eurasia. However, information on the effect of PWD on the host microbial community is limited. In this study, the bacterial community structure and potential function in the needles, roots, and soil of diseased pine were studied under field conditions using Illumina MiSeq coupled with Phylogenetic Investigation of Communities by Reconstruction of Unobserved states (PICRUSt) software. The results showed that the community and functional structure of healthy and diseased trees differed only in the roots and needles, respectively (p < 0.05). The needles, roots, and soil formed unique bacterial community and functional structures. The abundant phyla across all samples were Proteobacteria (41.9% of total sequence), Actinobacteria (29.0%), Acidobacteria (12.2%), Bacteroidetes (4.8%), and Planctomycetes (2.1%). The bacterial community in the healthy roots was dominated by Acidobacteria, Planctomycetes, and Rhizobiales, whereas in the diseased roots, Proteobacteria, Firmicutes, and Burkholderiales were dominant. Functionally, groups involved in the cell process and genetic information processing had a higher abundance in the diseased needles, which contributed to the difference in functional structure. The results indicate that PWD can only affect the host bacteria community structure and function in certain anatomical regions of the host tree.

Soil microorganisms and extracellular enzymes play important roles in soil nutrient cycling. Currently, China has the second-largest area of eucalyptus plantations in the world. Information on the effects of eucalyptus age and species of trees on soil microbial biomass and enzyme activities, however, is limited. In this paper, the soil microbial biomass and enzyme activities were studied in eucalyptus plantations with different ages (1 and 5+ years) and species of trees (E. urophylla×E. grandis, E. camaldulens and E. pellita) in South China. The results showed that both plantation age and eucalyptus species could affect the total microbial biomass and fungal biomass, whereas the bacterial biomass was affected only by plantation age. The fungal biomass and the fungi-to-bacteria ratio significantly increased along with increasing plantation age. Similarly, the plantation age and eucalyptus species significantly affected the enzyme activities associated with carbon cycling (β-xylosidase, β-d-glucuronidase, β-cellobiosidase and β-glucosidase). The activities of β-d-glucuronidase and β-glucosidase were significantly higher in the E. camaldulens plantation. The enzymes involved in nitrogen (N-acetyl-glucosamidase) and sulfur (sulfatase) cycling were only affected by the eucalyptus plantation age and species, respectively. The results highlight the importance of the age and species of eucalyptus plantations on soil microbial activities.

Pine wilt disease (PWD), caused by pinewood nematode (PWN) Bursaphelenchus xylophilus, is globally one of the most destructive diseases of pine forests, especially in China. However, little is known about the effect of PWD on the host microbiome. In this study, the fungal community and functional structures in the needles, roots, and soil of and around Pinus thunbergii naturally infected by PWN were investigated by using high-throughput sequencing coupled with the functional prediction (FUNGuild). The results showed that fungal richness, diversity, and evenness in the needles of diseased trees were significantly lower than those of healthy ones (p < 0.05), whereas no differences were found in the roots and soil. Principal coordinate analysis (PCoA) showed that the fungal community and functional structures significantly differed only in the needles of diseased and healthy trees, but not in the soil and roots. Functionally, the saprotrophs had a higher abundance in the needles of diseased trees, whereas symbiotrophs abundance was higher in the needles of healthy trees (linear discriminant analysis (LDA) > 2.0, p < 0.05). These results indicated that PWN infection primarily affected the fungal community and functional structures in the needles of P. thunbergii, but not the roots and soil.