NASA SOHO Mission,Yohkoh
science team
Ecological impacts of
UV-B radiation
Organismal effects and responses
Mycorrhizal fungi colonize plant
roots (ECO-SAFE)Microorganisms
Because microorganisms are single celled organisms, the effects of UV-B on them can be thought of in terms of molecular photobiology. UV is often used as a antimicrobial treatment for water, surfaces, and air (Madigan et al. 1999) but in the natural world, microorganisms, along with multicellular fungi are responsible for decomposition of organic materials and availability of nutrients.It has been assumed that soil microbes are relatively unaffected by UV-B radiation since it can only penetrate up to 100 microns into the soil surface. Johnson (2003) reviewed research on the responses of bacteria and fungi found on surfaces (epigeous), below the surface of the ground (hypogeous), and associated with plant roots (mycorrhizal fungi) to UV-B and observed that responses varied. More pigmented epigeous yeasts survived exposure to UV-B better than less pigmented ones, showing that some species are more well adapted to UV-B. Litter decomposition rates by hypogeous microorganisms were reduced when plants were exposed to UV-B, probably because of the indirect effects of different plant chemistry in the plants exposed to UV-B. Finally, in mycorrhizal fungus, the abundance of highly branched structures (arbuscules), believed to be sites of nutrient and carbon exchange between plants and fungus, was decreased by 69%. The only overall conclusion that Johnson (2003) was able to draw was that more, longer-term studies needed to be conducted to determine the effects of UV-B on microorganisms.
Regarding adaptation of microorganisms to UV-B, Miller et al. (2004) found that some species of Metarhizium, a pathogenic fungus, slowed growth during the stage in their germination when UV-B protective enzymes were lost and they were exposed to UV-B. The researchers concluded that these species were then able to repair damage before germination was continued and remain viable after UV-B exposure. Similarly, fungal abundance in a Tierra Del Fuego peatland was largely unaffected by exposure to near-ambient levels of UV-B but diversity was slightly lower under near-ambient UV-B as compared to a microfungal community exposed to sub-ambient levels of UV-B (Robson et al. 2004). The researchers concluded that the fungi were already adapted to the ambient levels of UV-B.
