The preconcentration/gas chromatography-mass spectrometry with FID detector method was used to observe the 115 atmospheric volatile organic compounds (VOCs) of Tai’an urban area in autumn 2020. The average volume fraction of VOCs during the observation period was (67.50±25.55)×10⁻⁹, dominated by alkanes (34.86%) and oxygenated volatile organic compounds (OVOCs) (32.03%). The atmospheric chemistry reactivity of VOCs was estimated using ozone formation potential (OFP) and the OH radical loss rate (L_OH), respectively. The OFP of Tai’an in autumn was (241.50±6.91)×10⁻⁹, mainly contributed by OVOCs (39.92%) and aromatics (33.03%). The calculated L_OH was 7.34±0.33 s⁻¹, which was dominated by OVOCs (56.32%). The contribution of VOCs to the potential for secondary organic aerosol (SOA) formation was estimated using the fractional aerosol coefficients (FAC), and the results showed that SOA formation potential was (366.58±37.80)×10⁻⁹, dominated by aromatics (98.79%). The results of the characteristic species ratio analysis showed that the VOCs of Tai’an in autumn were influenced by local sources such as traffic-related emissions, solvent use and combustion sources. The source apportionment results showed that the contribution of motor vehicle emissions to VOCs was the highest at 26.1%, with the contributions from gasoline vehicle exhaust emissions and diesel vehicle exhaust emissions being 19.4% and 6.7%. The contribution of solvent use and industrial sources to VOCs was comparable at 20.1% and 19.9%, respectively. The contribution of stationary combustion sources and liquefied petroleum gas (LPG) use was 16.2% and 12.3%, respectively. Biogenic sources contributed the lowest percentage of 5.4%.

To reveal the dynamic characteristics of root-associated fungal communities of P. sylvestris plantation, the co-occurrence network of root-associated fungi in P. sylvestris plantation were analyzed by using molecular ecological network analysis in the Mu Us Desert and its response to climate factors in different stand ages (27 a, 33 a and 44 a) and their annual growth stages (early growth season, vigorous growth season and end-of-growth season). The following conclusions are obtained. 1) Different growing seasons rather than different stand ages had significant differences in the co-occurrence network of fungi in roots of P. sylvestris plantation, and the co-occurrence network of fungi in roots was more complex in the vigorous growing season. 2) The keystone species of root-associated fungi of P. sylvestris plantation were significant in different growing seasons and stand ages. The keystone genera mainly included Geopora, Tomentella, Phaeosphaeria, Neocucurbitaria, Mortierella, etc. Ectomycorrhizal and saprophytic fungi were the keystone taxa in the early and end of the growth season, and saprophytic fungi and pathogens were the keystone taxa in the vigorous growth season. Meanwhile, the keystone taxa of middle-aged forest were saprophytic fungi and pathogens, while the mature forest were ectomycorrhizal and saprophytic fungi. 3) Relative humidity was the main influencing factor for ectomycorrhizal fungi network, and average precipitation and relative humidity were the main influencing factors for saprophytic fungi network and pathogens network (P<0.05). Therefore, the network dynamic of root-associated fungi of P. sylvestris plantation in different growing seasons was stronger than that of stand age in Mu Us Desert, and the co-occurrence network structure was more complex in the vigorous growth season. The root-associated fungal network was mainly affected by average precipitation and relative humidity. Saprophytic fungi played an important role in maintaining the stability of the fungal network in different stand ages and growing seasons. Saprophytic fungi and pathogens in the vigorous growth season with high precipitation and relative humidity, which potentially contributed to the growth and health of P. sylvestris plantation. 

To reveal the fungal community structure and functional groups in the roots associated with P. sylvestris, natural forest and different-aged plantations were analyzed using field investigation and molecular biotechnology in the Hulunbuir Sandy Land. 520 fungal OTUs were obtained from root tip samples of P. sylvestris, and belonged to 197 genera, 87 families, 5 phyla. Basidiomycota and Ascomycota had higher relative abundances, accounted for 54.98% and 39.27% respectively. The dominant bacteria in natural forest were Geminibasidium, Russula and Phialocephala, whereas the dominant bacteria in plantation were Suillus, Phialocephala and Tricholoma. Further, the relative abundance of other bacteria fluctuated with the stand age. The α diversity index of fungi in the roots of P. sylvestris plantation decreased gradually with the increasing of stand age. Among the different stands, the fungal diversity in the roots of mature forest was significantly lower than that in near-mature and middle-aged plantations as well as natural forest (P<0.05). Although the fungal community composition associated with P. sylvestris natural forest and plantations had stable variability, and near-mature forest is the closest to natural forest, natural forest and mature plantation obviously differed in the composition of fungal community. The proportion of symbiotic trophic fungi increased with the increasing of stand age. Conversely, the saprophytic and pathological trophic fungi decreased with the aging forest. The proportion of symbiotic trophic fungi in natural forest was similar with near-mature plantation, however saprophytic trophic fungi was the dominant type in natural forest. In the Hulunbuir Sandy Land, the fungal community in the root of P. sylvestris has complex structure and diverse species. The main functional groups are ectomycorrhizal and undefined saprophytic fungi. Some fungi show different ecological strategies in different stands.