Abstract: Aims The interaction of soil fungus-bacteria community is important for maintaining microhabitat balance, and changes in soil characteristics can affect the interaction mechanism of microflora. However, the understanding of fungus-bacterial co-occurrence pattern and how soil factors affect this patern are limited. To reveal the interactions of soil fungus-bacterial community of Pinus sylvestris var. mongolica plantations in the Horqin Desert, the soil samples were collected in the P. sylvestris var. mongolica plantations (middle age, near mature and mature) as well as the referenced sandy grassland. Methods Based on the 16S rRNA high-throughput sequencing technology, molecular ecological network analysis was used to compare and analyze the characteristics of soil fungus-bacteria network and its influencing factors of Pinus sylvestris var. mongolica plantation. Important findings The results showed that: (1) with the increase of forest age, the soil fungus-bacteria network became simpler. The fungus-bacterial community interaction is the most dense, the network anti-interference ability is the strongest, and the stability is the highest. Compared with pine plantation, soil fungus-bacteria network in sandy grassland was more complex. The synergistic relationship between bacterial communities was dominant in both plantation and sandy grassland, indicating that the interaction between bacterial communities was more intensive. (2) the key nodes of the soil fungus-bacteria network of different forest ages were different and all of them were bacterial OTU. The key nodes of the middle-age forest were the most numerous and Proteobacteria occupies the largest proportion. Acidobacteria is the key node in the symbiotic network of both the middle-age forest and the nearly mature forest. The results showed that Proteobacteria and Acidobacteria played a key role in maintaining the stability of the fungus-bacteria network, while the key nodes were not identified in the sandy grassland. (3) the complexity of soil fungus-bacteria network was mainly affected by soil available phosphorus and soil water content (P<0.05), and the stability of the network was significantly correlated with soil organic matter and available phosphorus content (P<0.05). The results of this study are helpful to further understand the characteristics of soil fungus-bacteria co-occurrence network and serve the sustainable management of P. sylvestris var. mongolica plantations.

Key words: Pinus sylvestris var. mongolica, microorganisms, co-occurrence network, soil, stand age