Stand age alters fungal community composition and functional guilds in subalpine Picea asperata plantations

Soil fungi participate in a variety of forest ecological processes and drive the succession of degraded forests. However, how the soil fungal community and functional taxa change with stand age remains unclear in sub -alpine plantations. We established five vegetation survey plots in four planted Picea asperata forests aged 25, 40, 50 and 75 years and one natural P. asperata forest aged approximately 200 years in a subalpine region and randomly collected rhizosphere and bulk soils of two representative P. asperata individuals in each plot for high-throughput sequencing of fungal communities and determination of soil properties. The fungal community composition in both rhizosphere and bulk soils varied significantly among different stand ages. Fungal opera-tional taxonomic unit (OTU) richness and Shannon diversity in bulk but not rhizosphere soil changed signifi-cantly with stand age. Except for the 75-year-old plantation, there was no difference in the fungal community composition between rhizosphere soil and bulk soil. Soil properties, plant production (P. asperata growth in-dicators) and plant richness jointly determined the fungal community composition, and soil total phosphorous (TP) accounted for the most variation in the fungal community. P. asperata regulated the community composition of fungal functional guilds (i.e., plant pathogens, saprophytes, ectomycorrhizal fungi and endophytes) mainly by changing soil properties rather than plant richness. Interestingly, the community composition of fungi and functional guilds in plantations became increasingly similar to that in the natural forest over time, and the fungal restoration rate (represented by the Bray-Curtis distance between plantations and natural forest) in bulk soil was faster than that in rhizosphere soil. In addition, with increasing stand age, the relative abundance of ectomy-corrhizal fungi increased, and the diversity of plant pathogens decreased, both of which were significantly associated with the reduction in soil total phosphorus. These results suggest that stand age is a major factor affecting soil fungal community variation in subalpine P. asperata plantations, which is largely dependent on soil property changes. In particular, soil TP may play a key role in the regulation of different ecological functional fungi.