Deep beneath the surface, a silent battle is taking place for the future of our planet's most fragile underground treasures.
The installation of artificial lighting in caves open to tourists—known as show caves—has created an unnatural problem: the explosive growth of photosynthetic organisms called lampenflora. These greenish biofilms of algae, cyanobacteria, and diatoms coat magnificent stalactites and ancient bone deposits, causing irreversible aesthetic, chemical, and physical damage. As the quest for sustainable solutions intensifies, scientists are turning away from harsh chemicals and exploring ingenious eco-friendly remedies to preserve these subterranean wonders for future generations.
Since the first cave was electrically lit for visitors over a century ago, a biological invasion has been unfolding in the darkness. The term "lampenflora" translates from German as "lamp flora," a name coined by botanist Klaus Dobat in the 1960s to describe the autotrophic lifeforms that colonize surfaces near permanent cave lighting .
These organisms, which include cyanobacteria, algae, diatoms, and even mosses, are not native to the dark zones of caves. Their spores and cells are carried in by air currents, water, animals, or the thousands of tourists who visit these underground attractions each year 8 . In the absence of natural competition, and fueled by the constant energy of artificial lights, they thrive on damp rock surfaces, speleothems (cave formations like stalactites and stalagmites), and even precious paleontological remains 1 .
The green patinas and crusts obscure the natural colors and features of cave formations 7 .
These microorganisms secrete organic acids that corrode limestone and other cave substrates 7 .
Biofilms can lead to increased porosity and exfoliation of the rock surface, sometimes leading to structural changes in delicate speleothems 5 .
The problem is so severe that it permanently closed the famous Lascaux cave in France in 1963 after a "successive ecological crisis" radically changed its conditions . Managing lampenflora has therefore become a critical task for conservationists and cave managers worldwide.
While traditional methods often rely on periodic bleaching with sodium hypochlorite, these chemicals can damage the underlying rock and are not a sustainable long-term solution 5 9 . In the search for eco-friendly alternatives, a promising study investigated the use of natural plant distillates to control lampenflora in the Zhijin Cave, Guizhou Province 4 .
Researchers designed an experiment to test the inhibitory effects of three plant distillates—mint, mugwort, and cinnamon—on the lampenflora microbial communities.
Lampenflora biofilm samples were collected from various lit surfaces within the Zhijin Cave.
The samples were treated with different concentrations of the three plant distillates. A control group was left untreated for comparison.
Researchers used DNA metabarcoding techniques to analyze the microbial communities after treatment. This involved sequencing specific genes (like the 16S rRNA for bacteria) to identify which organisms were present and in what quantities.
The inhibitory effect was measured by comparing the microbial diversity and richness in the treated samples to the control group. A significant reduction would indicate a successful treatment.
The results showed a clear winner in the fight against lampenflora.
| Plant Distillate | Effect on Bacterial Communities | Effect on Fungal Communities | Overall Efficacy |
|---|---|---|---|
| Mugwort | Most significant inhibition | Most significant inhibition | Most effective; significantly reduced microbial diversity and richness. |
| Mint | Moderate inhibition | Selective inhibition on certain fungal species | Moderately effective. |
| Cinnamon | Moderate inhibition | Moderate inhibition | Moderately effective. |
The core finding was that mugwort distillate had the most significant inhibitory effect. Samples treated with mugwort showed a dramatic reduction in both the diversity (number of different species) and richness (abundance of individuals) of the microbial community 4 . This is crucial because a resilient biofilm is often composed of a complex network of different organisms. By effectively disrupting this network, mugwort distillate undermines the entire structure of the lampenflora colony.
Mint and cinnamon distillates also showed inhibitory effects, but they were less potent. Interestingly, mint exhibited a selective effect, targeting certain species of fungi but leaving others relatively untouched 4 . This experiment provides a strong scientific foundation for using plant-based treatments, particularly mugwort, as a sustainable and environmentally friendly solution for managing lampenflora in sensitive cave environments.
Research into lampenflora control employs a diverse array of tools and techniques, from simple applications to high-tech technologies.
| Reagent/Material | Function | Key Characteristic |
|---|---|---|
| Plant Distillates (e.g., Mugwort) | Eco-friendly biocide that inhibits microbial growth. | Sustainable, biodegradable, and derived from natural sources 4 . |
| UV-C Light | Germicidal irradiation that bleaches and kills photosynthetic cells. | Physical treatment that leaves no chemical residue; requires specialized equipment 9 . |
| Benzalkonium Chloride | A quaternary ammonium compound that disrupts cell membranes. | Effective biocide, but its potential toxicity to non-target organisms requires careful consideration 9 . |
| Sodium Hypochlorite | Strong oxidizer (bleach) that kills microorganisms and bleaches pigments. | Common traditional treatment, but can damage speleothem surfaces and is not eco-friendly 5 9 . |
| PAM Fluorimeter | A device that measures chlorophyll concentration to estimate biofilm density. | Provides instantaneous, in-situ data without damaging the cave surface 1 . |
| Portable Spectrometer | Used to analyze the chemical "fingerprint" of surfaces via reflectance spectra. | Non-destructive tool for monitoring biofilm growth and composition 7 . |
The fight against lampenflora is not fought on a single front. Beyond finding the perfect treatment, scientists and cave managers are exploring integrated strategies that focus on prevention.
Since lampenflora depends on light, reducing exposure is fundamental. Strategies include using motion-sensor systems that only illuminate passages when tourists are present, installing lights further away from vulnerable surfaces, and shifting from broad-spectrum lights to those with wavelengths less usable by photosynthesis 7 .
Understanding the substrate preference of different organisms is another vital area of research. A 2025 study in the Toirano Cave in Italy revealed that diatoms have a higher concentration on ancient bones compared to rock or soil, while green algae prefer rock and soil substrates 1 .
Ecological studies are tracing the origins of lampenflora. Research in Lehman Caves in the Great Basin found that its lampenflora communities were distinct from those in nearby unlit caves, suggesting an unidentified source, potentially linked to human visitors 5 .
The data from these various strategies can be complex, as seen in the table below, which models how different lampenflora groups might respond to light reduction.
| Photosynthetic Microorganism | Substrate Preference | Predicted Response to Reduced Light Intensity |
|---|---|---|
| Cyanobacteria | No clear substrate preference; increases with light. | Strong decrease 1 . |
| Green Algae | Rock and soil substrates. | Strong decrease 1 . |
| Diatoms | Prefer bone substrates. | Weaker decrease on bones, making them potentially more persistent 1 . |
The preservation of the world's show caves is a delicate balancing act between making these geological marvels accessible to the public and protecting their pristine integrity. The growth of lampenflora is a direct consequence of human intrusion, but so too is the solution. Through continued research into eco-friendly treatments like plant distillates, smart lighting technologies, and a deeper understanding of cave ecology, we can develop sustainable strategies to combat the "green sickness." The goal is not merely to clean the caves but to ensure that our fascination with these underground worlds does not become the reason for their degradation, allowing their natural beauty to endure, unblemished, for centuries to come.