Change in microbial comm unities, soil enzym e and metabolic activity in a Torreya grandis plantation in response to root rot disease

Soil microorganisms have a profound influence on plant growth, but as well on plant disease. It is still not clear, however, how microbial community structures and functional activities are changing in transitions between healthy and diseased soils. We performed detailed bacterial and fungal community analysis in healthy and root- rot diseased soils of Torreya grandis plantation forest in the subtropical region of China. Soil enzyme activities and microbial metabolic profiling was done to find their interactions with the diseased plants and the microbial functioning. The diseased trees showed lower root biomass, total chlorophyll and N contents in leaf, but higher peroxidase activity. The soils under diseased trees had lower soil organic carbon (SOC) content, but higher pH, moisture and available N content. The microbial diversity was unchanged between the healthy and diseased soils, but the diseased soils had lower 16S rRNA and ITS gene copy numbers. Illumina MiSeq sequencing showed that the fungal rather than the bacterial community composition differed significantly (P < 0.05) and Gibberella and Cryptococcus were associated with the diseased trees. The activities of beta-D-cellobiosidase, beta-glucosidase and peroxidase and microbial carbohydrate utilization rates were typically enhanced in the diseased soils. Changes in SOC, available N and soil moisture associated to root-rot disease were key factors shaping microbial community composition and activity, and closely linked to plant biomass. Our study showed that prolonged root-rot infestation decreased tree vitality and soil microbial biomass, changed fungal community composition and soil functioning towards a faster organic C decomposition, which potentially may increase soil organic matter turnover.