Abstract
Tundra ecosystems have experienced an increased frequency of fire, and this trend is predicted to continue throughout the 21st Century. Post-fire recovery is underpinned by complex interactions between microbial functional groups that drive nutrient cycling. Here we use a mechanistic model to demonstrate an acceleration of the nitrogen cycle post-fire driven by changes in niche space and microbial competitive dynamics. We show that over the first 5-years post-fire, fast-growing bacterial heterotrophs colonize regions of the soil previously occupied by slower-growing saprotrophic fungi. The bacterial heterotrophs mineralize organic matter, releasing nutrients into the soil. This pathway outweighs new sources of nitrogen and facilitates the recovery of plant productivity. We broadly show here that while consideration of distinct microbial metabolisms related to carbon and nutrient cycling remains rare in terrestrial ecosystem models, they are important when considering the rate of ecosystem recovery post-disturbance and the feedback to soil nutrient cycles on centennial timescales.
Highlights
Tundra ecosystems have experienced an increased frequency of fire, and this trend is predicted to continue throughout the 21st Century
We evaluated the model against data collected from the severe 2007 Anaktuvuk River fire
A more recent analysis of plant functional types (PFTs) composition at this site has demonstrated a shift in the community a decade post-fire
Summary
Tundra ecosystems have experienced an increased frequency of fire, and this trend is predicted to continue throughout the 21st Century. How abrupt disturbances, such as fire, shape ecosystem responses to climate change, including to soil carbon stocks, remains uncertain. Shrubs tend to produce litter with higher carbon to nitrogen ratios, encouraging the growth of fungi with lower nitrogen requirements relative to bacteria[37] This pattern is important as the role fungi play in soil carbon cycling can be distinct from that of bacteria, partly because fungi produce chemically recalcitrant biomass, which slows rates of decomposition[38]. The model, which includes mechanistic representations of carbon, water, nitrogen, and phosphorus dynamics in plants and soils, has been successfully applied in dozens of sites around the world, with many studies focusing on high-latitude ecosystems[41,42,43,44,45].
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