Infrared Light, Soil Health, and the Mycorrhizal Web Under Climate Change

Introduction

Soil is more than a substrate for plants—it is a living matrix that underpins the stability of global ecosystems. Within this matrix, mycorrhizal fungi create extensive networks that connect plants to nutrients, regulate the soil microbiome, and help ecosystems adapt to changing conditions. These networks are finely tuned to their microenvironment, and when destabilized, the collapse ripples across entire landscapes.

In discussions of climate change, the most visible stressors—temperature extremes, droughts, and floods—often overshadow more subtle but equally significant influences. Among these is infrared (IR) radiation, the segment of the solar spectrum that provides thermal energy to soils and living organisms. While IR is less discussed than ultraviolet or visible light, its role in soil stability and microbial health is profound. Infrared regulates soil temperature, moisture dynamics, and oxidative stress, all of which shape the resilience of mycorrhizal systems. Laboratory work suggests that microbial enzymatic activity, particularly enzymes involved in carbon cycling, can respond positively to IR exposure by reducing oxidative stress and maintaining functional stability.¹ The broader photobiology literature—though centered on plants and animals—also shows IR wavelengths can modulate reactive oxygen species and metabolic efficiency, implying that diminished IR reaching soils (via aerosol load, cloudiness, or land-use change) could subtly erode fungal resilience over time.²

Mycorrhizal Ecology

Mycorrhizal fungi are ancient symbionts—over 90% of vascular plants form mycorrhizae that extend root foraging and transform nutrient dynamics.³ Two guilds dominate: arbuscular mycorrhizal fungi (AMF), common in grasslands and the tropics, and ectomycorrhizal fungi (EMF), prominent in temperate and boreal forests. Both influence carbon cycling and storage through biomass, exudates, and soil-aggregate formation.⁴ Mycorrhizae secrete glycoproteins (e.g., glomalin) that act as “soil glue,” stabilizing aggregates against erosion and enhancing porosity and water retention; when fungal networks degrade, structural failure accelerates nutrient loss beyond what plant traits alone can prevent.⁵ Although fungi lack photosynthesis, their colonization, hyphal extension, and spore germination depend on buffered microclimates—temperature, humidity, and oxygen regimes that IR helps stabilize, especially across diurnal cycles.⁶ In today’s climate, these fungi sit at the nexus of multiple stressors, and their failure often precedes visible plant decline—revealing the belowground infrastructure that governs whether ecosystems adapt or collapse.⁷

Climate Change and the Hydrocycle

A more “flashy” hydrocycle—prolonged drought punctuated by intense rainfall—now characterizes many regions. Drought fractures hyphal continuity; deluge and waterlogging reduce oxygen diffusion; rapid oscillation prevents recovery. In the Amazon, throughfall-exclusion experiments demonstrate that drought reduces AM colonization across diverse host species, including canopy trees—pointing to fungal vulnerability rather than plant-specific weakness.⁸ In North American temperate forests, long-term soil warming with altered precipitation has reduced EM richness and shifted communities, increasing soil respiration and destabilizing carbon storage even as tree assemblages remain.⁹ In Mediterranean systems, irregular rainfall coupled with acidification undermines fungal communities in drought-tolerant oaks and olives alike, emphasizing that stress propagates through the mycorrhizal web rather than plant genotype.¹⁰ Semi-arid Inner Mongolian grasslands show reduced fungal richness and hyphal density under altered rainfall across multiple grasses—again a soil–fungus signal rather than a host-specific one.¹¹ In boreal and permafrost zones, thaw alternates with waterlogging and drying; EM biomass declines often precede tree mortality and compositional change.¹²

Soil pH and Biogeochemical Shifts

Three processes intensify acidification: wet deposition of nitric and sulfuric acids, increased leaching of base cations under heavier rains, and higher soil CO₂ forming carbonic acid. Together they raise [H⁺], lower pH, and deplete buffering Ca²⁺, Mg²⁺, K⁺, and Na⁺ essential for fungal and plant function.¹³ Below pH ≈ 5.5, aluminum solubilizes to Al³⁺, binding to hyphal tips and root cell walls, impairing membrane integrity, enzyme secretion, and mycorrhizal colonization; Al³⁺ also complexes phosphorus, rendering it unavailable.¹⁴ Long-term acid rain and cation depletion have driven declines in sugar maples and their fungal partners in the northeastern U.S., illustrating ecosystem-scale consequences of base-cation loss.¹⁵ Across pH gradients, fungi and bacteria respond differently; extreme acidity suppresses both, with bacteria often rebounding faster—shifting decomposition toward rapid turnover and away from the stable aggregates fungi build.¹⁶ In Mediterranean oak and olive groves, Al³⁺ toxicity and Ca²⁺ depletion correlate with mycorrhizal collapse and reduced drought resilience, independent of host genotype.¹⁷

Infrared and Soil Microclimates Under Stress

IR governs surface energy balance: near-IR warms by day; longwave IR emitted by surfaces and canopy slows nocturnal cooling. When IR flux is perturbed by aerosol dimming, cloudiness, canopy loss, or snowpack shifts, soils experience greater diurnal thermal amplitude—raising oxidative stress and disrupting enzyme kinetics and spore viability.¹⁸ Experimental IR-heater studies provide mechanistic evidence: in California annual grasslands, IR warming increased AM hyphal length (>40%) yet reduced aggregate water stability via lower glomalin—growth gains offset by structural losses.¹⁹ Across semi-arid grasslands, warming generally decreased AM root colonization, implicating moisture stress as the proximate driver across hosts.²⁰ In temperate forests, long-term soil warming restructured EM communities toward faster, less mutualistic types, with consequences for carbon retention.²¹ At boreal edges, warming reduced EM biomass and favored saprotrophs—guild shifts not tied to a single tree species.²

Case Studies Across Biomes (Illustrative Summaries)

Amazon Basin — Drought reduces AM colonization across canopy and understory plants; nutrient acquisition falters when fungal partners decline.²³

Temperate Forests (USA) — Soil warming shifts EM communities and accelerates soil respiration despite stable tree assemblages.²⁴

Mediterranean Woodlands — Irregular hydrocycles plus acidification disrupt EM networks in oaks and olives; Al³⁺ toxicity and Ca²⁺ loss are key.²⁵

Inner Mongolian Grasslands — Altered rainfall lowers fungal richness and hyphal density across grass hosts; soil carbon retention drops.²⁶

Boreal/Permafrost Zones — Thaw–waterlogging cycles reduce EM biomass ahead of visible tree decline.²⁷

High-Latitude/Arctic Systems — Snowpack loss changes longwave balance and subnivean stability; colonization drops as soil microclimates swing.²⁸

Toward a General Theory of Soil Stress

Three drivers converge on the underground keystone: IR flux shifts, hydrocycle instability, and soil chemistry change (pH and cations). Together they destabilize soil microclimates (temperature, oxygen, moisture), inhibit mycorrhizal colonization and hyphal integrity, erode aggregate stability, and reroute carbon and nutrients. The consistent cross-biome pattern—fungal decline preceding plant failure—argues that resilience resides in the fungi–soil nexus.

Implications for Agriculture and Conservation

Practice: Maintain canopy and residue cover to buffer IR and moisture; minimize acidifying inputs; monitor and, where appropriate, restore base cations; design drainage in flood-prone sites and organic-matter accrual in drought-prone ones; consider IR-spectrum management in controlled environments.

Theory: Advance fungal photobiology under IR, integrate triadic stressors in models, and use fungal communities as early-warning indicators of ecological instability.

Conclusion

Soil is not inert ground but a breathing interface where light, water, and chemistry meet life. Infrared light—often ignored—helps hold the microclimate steady; hydrocycles and pH either support or erode that balance. Across forests, grasslands, and coasts, decline begins in the fungus before it is seen in the leaf. Caring for mycorrhizae is caring for the conditions of our own endurance.

Endnotes

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