Arbuscular mycorrhizal fungal response to fire and urbanization in the Great Smoky Mountains National Park

Abstract

Wildfires are increasing in frequency and intensity as drier and warmer climates increase plant detrital fuel loads. At the same time, increases in urbanization position 9% of fire-prone land within the United States at the wildland–urban interface. While rarely studied, the compounded effects of urbanization and wildfires may have unknown synergistically negative effects on ecosystems. Previous studies at the wildland–urban interface often focus on aboveground plant communities, but belowground ecosystems may also be affected by this double disturbance. In particular, it is unclear how much fire and urbanization independently or interactively affect nutritional symbioses such as those between arbuscular mycorrhizal (AM) fungi and the majority of terrestrial plants. In November 2016, extreme drought conditions and long-term fire suppression combined to create a wildfire within the Great Smoky Mountains National Park and the neighboring exurban city of Gatlinburg, TN. To understand how the double disturbance of urbanization and fire affected AM fungal communities, we collected fine roots from the 5 dominant understory species in September 2018 at each of 18 sites spanning 3 burn severities in both exurban and natural sites. Despite large variation in burn severity, plant species identity had the largest influence on AM fungi. AM fungal colonization, richness, and composition all varied most among plant species. Fire and urbanization did influence some AM fungal metrics; colonization was lower in burned sites and composition was more variable among exurban locations. There were no interactions among burn severity and urbanization on AM fungi. Our results point to the large influence of plant species identity structuring this obligate nutritional symbiosis regardless of disturbance regime. Therefore, the majority of AM fungal taxa may be buffered from fire-induced ecosystem changes if plant community composition largely remains intact, plant species life history traits allow for AM fungal persistence after fire disturbance, and/or nearby undisturbed habitat can act as an inoculum source for recolonization following fires. Thus, it is critical to maintain natural, undisturbed habitats interspersed within the wildland–urban interface.

Temporal continuity of habitat strengthens covariation between plant and arbuscular mycorrhizal fungal communities

“…Although Pressler et al . (2019) described a decrease in fungal biomass after fires in grasslands, whether prescribed fires or wildfires, in cases where the plant community composition remains largely intact, the AMF flora may easily recover after prescribed burns (Kivlin et al ., 2021).…”

“…Prescribed burns during the dormant season have little effect on hemicryptophytes and geophytes on account of the low heat conductivity of the soil and rapid combustion of plant residues. Although Pressler et al (2019) described a decrease in fungal biomass after fires in grasslands, whether prescribed fires or wildfires, in cases where the plant community composition remains largely intact, the AMF flora may easily recover after prescribed burns (Kivlin et al, 2021).…”

The interaction between land‐use change and fire regimes, directly and indirectly, affects the urban avian assemblages of Darwin, Australia

“…Conversely, Kivlin et al (2021), investigated the response of mycorrhizal fungi to urbanization and fire in the United States and while they found that urbanization and fire affected some fungal metrics independently, no interaction between urbanization and fire was identified. However, neither of these studies involved vertebrate species and all sampling sites were within either National or State parks surrounded by urban zones.…”

“…Beal‐Neves et al ( 2020 ), using time since fire as a variable, examined fire disturbance and urbanization on pollinating faunas, specifically insects, in South Brazilian grasslands and found that fire disturbance events became more frequent with an increase in urbanization; further, they found that the richness of floral visitors was positively correlated with an increase in urbanization. Conversely, Kivlin et al ( 2021 ), investigated the response of mycorrhizal fungi to urbanization and fire in the United States and while they found that urbanization and fire affected some fungal metrics independently, no interaction between urbanization and fire was identified. However, neither of these studies involved vertebrate species and all sampling sites were within either National or State parks surrounded by urban zones.…”