Abstract
In Appalachian ecosystems, forest disturbance has long-term effects on microbially driven biogeochemical processes such as nitrogen (N) cycling. However, little is known regarding long-term responses of forest soil microbial communities to disturbance in the region. We used 16S and ITS sequencing to characterize soil bacterial (16S) and fungal (ITS) communities across forested watersheds with a range of past disturbance regimes and adjacent reference forests at the Coweeta Hydrologic Laboratory in the Appalachian mountains of North Carolina. Bacterial communities in previously disturbed forests exhibited consistent responses, including increased alpha diversity and increased abundance of copiotrophic (e.g., Proteobacteria) and N-cycling (e.g., Nitrospirae) bacterial phyla. Fungal community composition also showed disturbance effects, particularly in mycorrhizal taxa. However, disturbance did not affect fungal alpha diversity, and disturbance effects were not consistent at the fungal class level. Co-occurrence networks constructed for bacteria and fungi showed that disturbed communities were characterized by more connected and tightly clustered network topologies, indicating that disturbance alters not only community composition but also potential ecological interactions among taxa. Although bacteria and fungi displayed different long-term responses to forest disturbance, our results demonstrate clear responses of important bacterial and fungal functional groups (e.g., nitrifying bacteria and mycorrhizal fungi), and suggest that both microbial groups play key roles in the long-term alterations to biogeochemical processes observed following forest disturbance in the region.
Highlights
Land use change has modified 75% of ice-free terrestrial ecosystems (Ellis, 2011), with conversion of forests to managed states being one of earth’s dominant land conversions (Vitousek et al, 1997; Foley et al, 2005; Rudel et al, 2005)
Variation partitioning showed soil chemistry accounting for 37% of observed variation in bacterial communities, 29% of which was independent of vegetation communities (Figure 3C)
Vegetation communities accounted for 16% of observed variation in bacterial communities, 8% of which was independent of soil chemistry (Figure 3C)
Summary
Land use change has modified 75% of ice-free terrestrial ecosystems (Ellis, 2011), with conversion of forests to managed states (e.g., agriculture, timber plantations) being one of earth’s dominant land conversions (Vitousek et al, 1997; Foley et al, 2005; Rudel et al, 2005). The extent of anthropogenic forest conversion continues to accelerate in the 21st Century (Drummond and Loveland, 2010; Hansen et al, 2010; Watson et al, 2014), highlighting the need to characterize impacts of forest disturbance on terrestrial biodiversity and ecosystem functions Understanding these impacts is critical from a biogeochemical perspective, as forested ecosystems are central components of Earth’s elemental cycles and provide ecosystem services that support human well-being, including storage of carbon (C), regulation of nutrient cycles, and provisioning of clean drinking water (Millenium Ecosystem Assessment, 2005). These prior studies suggest that forest soil microbial community shifts in response to disturbance are likely to occur, no studies to our knowledge have fully characterized long-term (i.e., several decades) responses of both soil bacterial and fungal communities to several different past disturbances (e.g., timber harvest, agricultural conversion, and timber plantation conversion) simultaneously in temperate forests
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