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Soil fungi play a critical role in the carbon and nutrient cycling of forest ecosystems. Identifying the composition of soil fungi in response to the broadleaf restoration of Pinus massoniana plantation is essential for exploring the mechanistic linkages between tree species and ecological processes, but remains unexplored. We compared the shifts in soil fungal diversity and guilds by high–throughput sequencing between two P. massoniana plantations at different stand ages, two modes of restoration with broadleaf trees, and a secondary forest in subtropical China. We found that soil fungal taxonomic and functional compositions significantly differed among forests. The highest Chao 1, Shannon, and phylogenetic diversity indices were consistently observed in the two P. massoniana monocultures, followed by the two modes of broadleaf mixing, and the secondary forests. Fungal communities transitioned from Ascomycota-dominated at P. massoniana plantations to Basidiomycota-dominated at other forests in the topsoil. Furthermore, saprotrophs and symbiotrophs were favoured in plantations and secondary forests, respectively. Soil pH exerted the most significant effect on the relative abundance of Ascomycota and Rozellomycota, as well as the saprotrophs. Moreover, the dominant phyla of Ascomycota, Mucoromycota, and Rozellomycota were negatively related to soil microbial biomass nitrogen, ammonium nitrogen, and total nitrogen contents; however, Mortierellomycota benefited from the elevated soil ammonium nitrogen content. On the other hand, soil nitrate nitrogen and available phosphorus contents strongly and negatively influenced the ectomycorrhizal fungi, while the other fungal guilds were mainly affected by soil pH. Our findings guide an evaluation of the consequences of forest restoration and contribute to an improved understanding of the mechanisms behind soil biogeochemical cycling in subtropical forest ecosystems. [ABSTRACT FROM AUTHOR]

To explore the response of nitrogen metabolism in Masson pine (Pinus massoniana) to high CO2 concentrations, needles from one-year-old seedlings were used as materials to detect key enzyme activities, gene expression and different forms of nitrogen metabolites after CO2 stress for different durations (0 h, 6 h, 12 h, 24 h). The results show that elevated CO2 affected the efficiency of nitrogen metabolism in Masson pine needles, inhibiting the expression of key genes involved in nitrogen metabolism, including glutamate synthase (GOGAT), nitrite reductase (NiR), glutamine synthase (GS), nitrate reductase (NR) and glutamate dehydrogenase (GDH), and decreasing the activities of GOGAT, NiR, and GS. The decrease in enzyme activities and gene expression caused a decrease in different forms of nitrogen metabolites, including total nitrogen, ammonium, nitrite and specific amino acids. With prolonged stress, the nitrate content increased first and then decreased. In this study, the response pattern of nitrogen metabolism to CO2 stress in Masson pine needles was described, which may aid future research on nitrogen utilization in Masson pine. [ABSTRACT FROM AUTHOR]