[Effects of Lithology on the Abundance and Composition of Soil Nitrogen-fixing Bacteria and Arbuscular Mycorrhizal Fungal Communities in Karst Shrub Ecosystem].

Lithology is a key factor when used to restore vegetation in karst degraded ecosystems, and arbuscular mycorrhizal (AM) fungi and nitrogen-fixing bacteria play an important role in improving plant growth. However, little information is available regarding the effects of lithology on these two groups of microorganisms. To test whether these microbial communities are impacted by lithology, the abundance and composition of soil AM fungal and nitrogen-fixing bacteria communities were determined through terminal restriction fragment length polymorphism (T-RFLP) and real-time fluorescence-based quantitative PCR (real-time PCR). Three types of lithology (dolomite, limestone and dolomite-limestone) were selected in this study. The diversity, richness, and evenness of plant species were evaluated through field surveys and soil properties were measured. The results showed that the abundances of soil nitrogen-fixing bacteria and arbuscular mycorrhizal fungal communities were significantly influenced by lithology. The abundances of these two groups of microorganisms were the lowest in dolomite soil, inferior to dolomite-limestone soil, while highest in limestone soil. Similarly, the composition of soil nitrogen-fixing bacteria and AM fungi communities varied among lithology. A significant linear correlation was observed among soil organic carbon, available phosphorus, clay content and nitrogen-fixing bacterial abundance (<0.05), and a significant linear correlation among total nitrogen, clay content and AM fungal abundance (<0.05). Redundancy analysis showed that the composition of nitrogen-fixing bacterial community was closely linked to plant evenness, and the AM fungal community composition was closely linked to plant diversity (plant evenness, Shannon-wiener and richness). These results indicated that lithology influenced the abundances and compositions of soil nitrogen-fixing bacteria and arbuscular mycorrhizal (AM) fungal communities mainly through plant and soil properties.