Soil acidification induced decline disease of Myrica rubra: aluminum toxicity and bacterial community response analyses

The decline disease of Myrica rubra tree is commonly induced by soil acidification, which affects the yield and the quality of fruits. It is hypothesized that aluminum toxicity and microbial community changes caused by soil acidification were the main causes of decline of Myrica rubra tree. In order to explore the decline mechanism of Myrica rubra tree, soils around healthy and decline trees of Myrica rubra were collected to compare the concentrations of different aluminum forms, enzyme activities, and bacterial community structure. In this study, soil samples were collected from the five main production areas of Myrica rubra, Eastern China. The results showed that diseased soils had higher exchangeable aluminum, lower enzyme activities, and lower microbial diversity than healthy soils at various sites. The toxic Al significantly decreased bacterial diversity and altered the bacterial community structure. The diseased soils had significantly lower alpha-diversity indices (ACE, Chao1, and Shannon) of bacterial community. The Al toxicity deceased the relative abundance of Acidobacteria and Planctomycetes, while enhanced the relative abundance of Cyanobacteria, Bacteroidetes, and Firmicutes in soils. Co-occurrence network analysis indicated that the Al toxicity simplified the bacterial network. The soil ExAl content was significantly and negatively correlated with the nodes (r = -0.69, p < 0.05) and edges (r = -0.77, p < 0.01) of the bacterial network. These results revealed that the Al toxicity altered soil bacterial community structure, resulting in the decline disease of Myrica rubra tree, while highlighted the role of Al forms in the plant growth. This finding is of considerable significance to the better management of acidification-induced soil degradation and the quality of fruits.