Abstract
The intensity and frequency of ecosystem disturbances are shifting with climate change, and multiple disturbances in close succession have the potential to compound their independent effects and strongly alter ecosystem structure and function. In this paper, we examine the effects of an extreme precipitation event on a montane forest landscape that was previously decimated by wildfire (37 months prior) relative to an unburned site in the same ecosystem. We assessed responses in soil edaphic properties, bacterial community composition and assembly, and soil enzyme activities involved in carbon (C) and nitrogen (N) acquisition. Our research reveals that previously burned landscapes are susceptible to a subsequent extreme precipitation event via significant increases in soil pH where unburned soils are not. Beta- and Delta-proteobacteria associated with early succession increased and shifts were observed in N- vs. C-acquiring extracellular enzymes within burned soils after the extreme precipitation event. Finally, we connected variation in ecological selective pressures on bacterial communities associated with pH change to these differences in microbial mediated soil enzyme activity. Thus, this research demonstrates how multiple, compounding disturbances drive distinct changes relative to systems experiencing a single disturbance and suggests that changes in bacterial community assembly process with disturbance may underlie this response.
Highlights
IntroductionWith the effects of climate change resulting in increased forest wildfire activity in the westernUnited States, large areas of forest landscapes have and will experience high severity fires [1,2,3].Research efforts are expanding our understandings of how fires influence ecosystem properties including soil edaphic properties, microbial community structure, and ecosystem function [4,5,6,7,8,9], and are better demonstrating how forest ecosystems recover from fire over time [10,11,12]
In this work we show how montane landscapes that have previously experienced fire disturbance respond to extreme precipitation events in soil edaphic properties, bacterial community assembly, and ecosystem process (C and N cycling) as compared to adjacent unburned forest soils
While we acknowledge that a variety of other unmeasured edaphic properties, such as charcoal content or carbon/nitrogen chemistry etc., may respond to compounding disturbance with implications for microbial communities and requires further study, in this paper we focus on core edaphic properties that are well known to effect bacterial community structure and function
Summary
With the effects of climate change resulting in increased forest wildfire activity in the westernUnited States, large areas of forest landscapes have and will experience high severity fires [1,2,3].Research efforts are expanding our understandings of how fires influence ecosystem properties including soil edaphic properties, microbial community structure, and ecosystem function [4,5,6,7,8,9], and are better demonstrating how forest ecosystems recover from fire over time [10,11,12]. While efforts to understand fire disturbance are central in our ability to model ecosystem responses and better manage forest ecosystems both before and after fires [13,14,15,16], various other disturbance types are increasing in frequency, intensity, and scale, increasing the potential for burned landscapes to. Forest fires alone modify physical, chemical, and biological soil properties [19,20,21,22,23,24]. These fire-induced changes can be short-term or long-term, depending on the severity and frequency of fire, and post-fire climatic conditions [19,23]. During wildfires soils experience extreme temperatures, ranging from less than 100 ◦ C to well over 400 ◦ C [25], that change soil carbon (C) chemistry, nutrient pools, pH, and erosion potential, among other properties
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