# Influence of Soil Characteristics on Wood Biodeterioration by Brown Rot Fungi
## 4 Discussion  
Our study investigated the pH of soils around utility poles and factors that influence fungal activity and may possibly have an impact on premature failure of utility poles in the field. The impact of soil pH on the microbial community composition and its activity is one of the most important influential factors in natural environments. Previous studies by [PERSON] et al. [38] showed that, regardless of the soil, the fungal growth was directly associated with a pH of up to 7, but not above. This was confirmed in the present study that showed an average at approximately pH = 6.7 for all soil samples that were collected around utility poles that had previously failed in the field. The competitive fungal: bacterial growth ratio has also been demonstrated to be pH dependent in soils. Assuming that bacteria inhibit fungal growth at a pH above 7 and fungi take advantage of a pH below 7 [38], soils around the utility poles seem to have the perfect pH environment for brown rot fungi. In previous studies, [PERSON] et al. [13] showed that the failure of Cu-treated utility poles was mainly associated with brown rot fungi (_Antrodia_ spp.). In the latter study, a direct correlation between fungal species and geographic regions was not evident, but there was strong evidence that the type of wood preservative formulation had the highest selective pressure on wood decomposition by brown rot fungi. The results of the present study suggest that the soil pH may increase the microbial activity i.e., the biochemical cycling in soils in close proximity to Cu-impregnated utility poles. Different parameters have been postulated to assess the influence on the advantages of different communities [39] such as initial inoculum and rapidly growing species. To date, differences in pH tolerance on Cu-impregnated wood have not been addressed. Thus, our study suggests that brown rot fungi in the soil around utility poles may take advantage of the specific environmental conditions. Brown rot fungi have evolved to specifically breakdown cellulose and other polysaccharides from wood. The mechanisms of wood cellulose depolymerisation by brown rot fungi have been hypothesised to occur via the production of extracellular toxic oxygen radicals such as the highly reactive hydroxyl radical via the Fenton reaction [19; 40]. The role of iron in such reactions as well as other metabolic processes have been strongly documented. However, the bioavailability of iron is limited in the soil due to formation of insoluble metal oxides and hydroxides [41]. In our study, we showed that in the presence of iron dominant brown rot fungi such as _A. serialis_ can cause considerable decay in impregnated wood specimens. In previous studies by [PERSON] et al. [13], the influence of available Cu was evaluated for a range of brown rot fungi. It was evident that the same concentrations of Cu caused toxicity to all the studied fungi, whereas in this study iron did not have any negative influence on the activity of the fungi. Thus, as iron is essential for life and the iron levels in wood are usually significantly low [42; 43], the immobilisation/precipitation of essential ions from soils around the utility poles may also reduce the activity of brown rot fungi in the soil. Leaching of wood preservatives has been previously described as pH dependent but the absence of Cr as a fixative for Cu in wood strongly influences leaching [17]. Furthermore, wood properties such as pH, lignin type and content and extractive content can also influence the fixation of wood preservatives [44]. Copper and Cr compounds form more stable complexes with guaiacyl units of lignin which are the main monomer of softwood rather than the syringyl units that are the dominant monomer in secondary walls of hardwood fibres. This explains the fact that Cu in impregnated conifer wood migrates faster when substances with higher binding capacities are present such as HA or charcoal [17].