Ecological Drivers of the Soil Microbial Diversity and Composition in Primary Old-Growth Forest and Secondary Woodland in a Subtropical Evergreen Broad-Leaved Forest Biome in the Ailao Mountains, China

Abstract

Replacement of primary old-growth forests by secondary woodlands in threatened subtropical biomes drives important changes at the level of the overstory, understory and forest floor, but the impact on belowground microbial biodiversity is yet poorly documented. In the present study, we surveyed by metabarcoding sequencing, the diversity and composition of soil bacteria and fungi in the old-growth forest, dominated by stone oaks (Lithocarpus spp.) and in the secondary Yunnan pine woodland of an iconic site for biodiversity research, the Ailaoshan National Nature Reserve (Ailao Mountains, Yunnan province, China). We assessed the effect of forest replacement and other environmental factors, including soil horizons, soil physicochemical characteristics and seasonality (monsoon vs. dry seasons). We showed that tree composition and variation in soil properties were major drivers for both bacterial and fungal communities, with a significant influence from seasonality. Ectomycorrhizal Operational Taxonomic Units (OTUs) dominated the functional fungal guilds. Species richness and diversity of the bacterial and fungal communities were higher in the pine woodland compared to the primary Lithocarpus forest, although prominent OTUs were different. The slightly lower complexity of the microbiome in the primary forest stands likely resulted from environmental filtering under relatively stable conditions over centuries, when compared to the secondary pine woodlands. In the old-growth forest, we found a higher number of species, but that communities were homogeneously distributed, whereas in the pine woodlands, there is a slightly lower number of species present but the communities are heterogeneously distributed. The present surveys of the bacterial and fungal diversity will serve as references in future studies aiming to assess the impact of the climate change on soil microbial diversity in both old-growth forests and secondary woodlands in Ailaoshan.

The bacterial and fungal microbiomes of ectomycorrhizal roots from stone oaks and Yunnan pines in the subtropical forests of the Ailao Mountains of Yunnan

“…We have shown in our companion study (Zeng et al, 2022) that the edaphic features, such as soil pH and nutrient content, were significantly different in the Lithocarpus old-growth forest by comparison to the Pinus woodland. These differences in edaphic features influenced the soil microbial communities (Zeng et al, 2022), but also the ECM microbial communities (present study) as shown in other forest ecosystems (Peay et al, 2013;Liu et al, 2014Liu et al, , 2015He et al, 2017). Given that soil microbial communities feed the plant microbiome, both the reservoir of microorganisms in soil adjacent to roots and the soil edaphic Frontiers in Microbiology frontiersin.org parameters strongly influence the plant (Frey Klett et al, 2007;Bonito et al, 2014).…”

“…In addition to root exudates, hyphal exudates, such as trehalose, released by the various ECM fungi played an important role in recruiting bacterial and fungal microbiomes (Zhang et al, 2021). We have shown in our companion study (Zeng et al, 2022) that the edaphic features, such as soil pH and nutrient content, were significantly different in the Lithocarpus old-growth forest by comparison to the Pinus woodland. These differences in edaphic features influenced the soil microbial communities (Zeng et al, 2022), but also the ECM microbial communities (present study) as shown in other forest ecosystems (Peay et al, 2013;Liu et al, 2014Liu et al, , 2015He et al, 2017).…”

“…In the stone oak old-growth forest and the pine woodlands in Ailaoshan, ECM fungi, such as Russula, Lactarius and Lactifluus in the Russulaceae, were the most abundant OTUs detected in the soil fungal community, irrespective of the soil layers and season (Zeng et al, 2022). As shown by the present analyses, the fungal community of ECM roots was significantly different between the tree species and the sampling season had also a significant influence on this rootassociated mycobiome (Figure 1; Supplementary Table S1).…”

“…Mean annual precipitation is 1799 mm, 86% of which occurs during the monsoon rainy season from May to October (Song et al, 2017). Therefore, seasonal variability in soil water content is substantial (Wu et al, 2014) and influences the soil microbial communities (Zeng et al, 2022). As soil water content affects the soil mycobiome composition (Zeng et al, 2022) and competition between ECM and saprotrophic fungi (Baldrian, 2017), we surveyed the ECM root mycobiome at the end of the wet or dry seasons.…”

“…In a companion study, we surveyed by metabarcoding sequencing, the diversity and composition of soil bacteria and fungi in an old-growth forest, dominated by stone oaks (Lithocarpus spp.) and in a secondary Yunnan pine woodland in the subtropical Ailao Mountains in the Yunnan province, China (Zeng et al, 2022). Limited information exists on the alterations of soil microbiological characteristics in subtropical montane forests, while little is known of how the microbiome distribution pattern, life history and functional traits vary during forest replacement, e.g., old-growth Lithocarpus forest versus native pine woodlands.…”