During Impact Winter Scenarios: Modeling Fungal Proliferation as a Carbon Cycle Buffer

Introduction to Impact Winters and Ecological Resilience

The aftermath of an asteroid impact is not merely a geological catastrophe—it is a biological crucible. Among the most devastating consequences is the impact winter, a prolonged period of global cooling caused by atmospheric debris blocking sunlight. As temperatures plummet and photosynthesis declines, the carbon cycle—Earth’s metabolic pulse—faces disruption. Yet, within this chaos lies an unexpected stabilizer: radiation-resistant fungi.

The Role of Fungi in Carbon Sequestration

Fungi, often overlooked in climate models, are silent architects of carbon dynamics. Mycelial networks decompose organic matter, releasing CO₂, but they also stabilize carbon in soils through complex organic polymers like chitin and melanin. Under extreme cooling, these organisms may become dominant players:

• Decomposition Slowdown: Cold temperatures reduce microbial activity, but fungi like Cladosporium and Cryptococcus thrive in subzero conditions.
• Melanin as a Radiation Shield: Fungi such as Exophiala dermatitidis use melanin to absorb ionizing radiation, a likely byproduct of impact-induced atmospheric changes.
• Carbon Lock-in: Mycelial mats physically trap organic debris, delaying CO₂ release during periods of low photosynthetic uptake.

Modeling Post-Impact Fungal Proliferation

1. Temperature-Dependent Growth Curves

Adapting the Arrhenius equation for fungal metabolic rates, simulations show that below 5°C, bacterial competitors are suppressed while psychrophilic fungi maintain growth. Data from Antarctic permafrost isolates suggest a 20–40% increase in fungal biomass under simulated impact winter conditions.

2. Radiation Selection Pressure

Chernobyl’s "black fungi" (Wangiella dermatitidis) demonstrate melanin’s role in radiotropism. Models incorporating gamma radiation levels (0.5–2 Gy/day, based on K-Pg boundary estimates) show melanized fungi outcompeting non-melanized strains by 3:1 within 200 days post-impact.

3. CO₂ Buffering Capacity

Using the DeNitrification-DeComposition (DNDC) model modified for fungal dominance, a 10-year impact winter scenario projects:

• A 15–30% reduction in atmospheric CO₂ volatility due to fungal carbon immobilization.
• Delayed peak CO₂ release by 12–18 months compared to bacterial-dominated decomposition.

Case Study: The Cretaceous-Paleogene (K-Pg) Boundary

The K-Pg event (66 MYA) offers a paleontological testbed. Sedimentary biomarkers reveal:

• A 5–8x spike in fungal spores (e.g., Trichosporonites) immediately post-impact.
• Carbon isotope excursions suggesting fungal-mediated carbon retention in soils.

Implications for Future Planetary Resilience

Beyond catastrophe modeling, these findings redefine extremophiles’ role in biosphere stability. Key insights include:

• Fungal Inoculation as Geoengineering: Preemptive introduction of radiation-resistant strains to vulnerable ecosystems.
• Exobiology Applications: Fungal carbon buffers as a terraforming tool for Mars or icy moons.

Challenges and Unresolved Questions

The model has limitations:

• Trophic Cascades: Overproliferation may disrupt saprophytic food webs.
• Melanin’s Thermal Trade-off: Dark pigments could exacerbate local warming post-winter.

A Call for Interdisciplinary Research

This synthesis of paleoclimatology, mycology, and astrobiology demands collaboration. Priorities include:

• High-energy physics experiments on fungal radiation thresholds.
• Genomic sequencing of extremotolerant strains from impact craters.