Substrate and low intensity fires influence bacterial communities in longleaf pine savanna

Abstract

Bacterial communities associated with vegetation-soil interfaces have important roles in terrestrial ecosystems. These bacterial communities, studied almost exclusively in unburnt ecosystems or those affected by rare, high-intensity wildfires, have been understudied in fire-frequented grasslands and savannas. The composition of ground-level bacterial communities was explored in an old-growth pine savanna with a centuries-long management history of prescribed fires every 1–2 years. Using 16S metabarcoding, hypotheses were tested regarding differences in bacterial families of litter and soil surface substrates in patches of ground layer vegetation that were naturally burnt or unburnt during landscape-level prescribed fires. Litter/soil substrates and fire/no fire treatments explained 67.5% of bacterial community variation and differences, driven by relative abundance shifts of specific bacterial families. Fires did not strongly affect plant or soil variables, which were not linked to bacterial community differences. Litter/soil substrates and the naturally patchy frequent fires appear to generate microhabitat heterogeneity in this pine savanna, driving responses of bacterial families. Prescribed fire management may benefit from considering how fire-altered substrate heterogeneity influences and maintains microbial diversity and function, especially in these fiery ecosystems. Frequent, low-intensity fires appear ecologically important in maintaining the diverse microbial foundation that underlie ecosystem processes and services in fire-frequented habitats.

Fuel buildup shapes post-fire fuel decomposition through soil heating effects on plants, fungi, and soil chemistry

“…Due to logistical limitations, we could not track many ecosystem properties over the year following fire, but immediate fire responses of the system still helped predict decomposition shifts. Litter fungi were more impacted by fire than soil fungi, especially with large fuel additions, which supports an insulating role for soil shown in previous findings (Dao et al, 2022; SemenovaLJNelsen et al, 2019). These rapid (∼1-2 months) fungal responses to fire were directly tied to changes in decomposition much later, at 4 and 6 months after fire (Fig.…”

“…The spatial heterogeneity of the pine canopy creates variation in fire severity through differences in pine needle and grass fuel loads (Ellair and Platt, 2013; Platt et al, 2016b; Sánchez-López et al, 2023). Previous work in this system has linked variation in fire severity and frequency to changes in fungal (SemenovaLJNelsen et al, 2019) and bacterial communities (Dao et al 2022), as well as reduced decomposition (Hopkins et al, 2020). In this experiment, we manipulated fine fuels in plots near and away from canopy pines to test how fuel loads and heat release influenced soil conditions, plant communities, fungal communities, and the microbial decomposition of post-fire plant fuels.…”