pH, and increases in the level of root respiration as well as the quantity of roots. The fungus also decreases the organic carbon and nitrogen concentrations. Soil with the mycelium becomes more podzolized than the surrounding soil. Conservation Some Hydnellum species have been shown to be in decline in Europe, including the Czech Republic, the Netherlands, Norway, and Scotland. In the United Kingdom, several are listed in the biodiversity action plan for stiped hydnoid fungi: H. aurantiacum is classified as critically endangered; H. caeruleum, H. ferrugineum are listed as endangered, while H. concrescens, H. spongiosipes, H. peckii, and H. scrobiculatum are considered vulnerable. H. ferrugineum and H. peckii are sensitive to the increased nitrogen deposition resulting from clear-cutting, a forestry practice used in some areas of Europe. Conservation efforts for Hydnellum are hindered by the fact that some species are difficult to discriminate in the field, making it hard to determine an appropriate conservation status. Techniques based on species-specific PCR primers and DNA extraction from soil have been developed to detect the mycelia of various Hydnellum species without having to rely on the presence of fruitbodies, which may help conservation efforts as well as improve understanding of below-ground ecology. Similar techniques have been used to show that, in the case of H. aurantiacum and H. caeruleum, the fungus can persist below the ground for at least four years without producing fruitbodies. Bioactive compounds Several chemical compounds—some with unique biological activity—have been isolated and identified from Hydnellum species. For example, Hydnellum peckii contains atromentin, a pigment with anticoagulant properties similar to heparin. Atromentin also possesses antibacterial activity, inhibiting the enzyme enoyl-acyl carrier protein reductase (essential for the biosynthesis of fatty acids) in the bacteria Streptococcus pneumoniae. Some species are used as dyes. Hydnellum caeruleum, used in North America and Scandinavia to dye silk and wool, produces a range of colors including tan, blue, and forest-green, depending on the mordant that is used. Hydnellum peckii produces gray, brown, and olive colors. Hydnuferrugin and hydnuferruginin are pigments responsible for the coloration of H. ferrugineum and H. zonatum. Geogenin is a yellow pigment found in H. geogenium. Thelephoric acid is present in several Hydnellum species. This compound, derived metabolically from the shikimic acid pathway, inhibits the enzyme prolyl endopeptidase, which is involved in deteriorating certain neuropeptides that are believed to contribute to memory and learning. Hydnellum caeruleum and H. concrescens have several para-terphenyl derivatives