Colonization by Tuber melanosporum and Tuber indicum affects the growth of Pinus armandii and phoD alkaline phosphatase encoding bacterial community in the rhizosphere

The synthesis of truffle ectomycorrhizae and the ecology of truffle-colonized seedlings in the early symbiotic stage are important for the successful truffle cultivation. In this study, two black truffle species, Tuber melanosporum and Tuber indicum, were selected to colonize Pinus armandii seedlings. 2, 4, 6 and 8 months after inoculation, the growth performance of the host and the rhizosphere soil properties were detected. The dynamic changes of two mating type genes in substrate were also monitored to assess the sexual distribution of truffles. Additionally, the variation of soil bacterial communities encoded by phoD alkaline phosphatase genes was investigated through next-generation sequencing. The results indicated that both T. melanosporum and T. indicum colonization promoted the growth of P. armandii seedlings to some extent, including improving their biomass, total root surface area, root superoxide dismutases and peroxidase activity. The organic matter and available phosphorus in rhizosphere soil were also significantly enhanced by two truffles' colonization. The phoD-harboring bacterial community structure was altered by both truffles, and T. melanosporum decreased their diversity or richness on the 6th and 8th month after inoculation. Pseudomonas, Xanthomonas, and Sinorhizobium, a N₂-fixer with phoD genes, were found more abundant in truffle-colonized treatments. The mating type distribution of the two truffles was uneven, with MAT1-1-1 gene occupying the majority. Overall, T. melanosporum and T. indicum colonization affected the micro-ecology of truffle symbionts during the early symbiotic stage. These results could give us a better understanding on the truffle-plant-soil-microbe interactions, which would be beneficial to the subsequent truffle cultivation.

Keywords: Ectomycorrhizae; Mating type genes; Microbes; Truffle; phoD genes.