Assessing the relative bioavailability of copper to fungi degrading treated wood

Copper is ubiquitous as a biocide component in wood preservatives. Some fungi detoxify copper by immobilizing copper ions with oxalate, decreasing its physiological availability (bioavailability). Decreases in copper bioavailability may also occur during wood treatment. To date, however, copper retention in wood has been measured as overall weight-to-volume concentration without an estimate of its bioavailability and without assessment of its relative contribution to preservative efficacy. Here, we gauge the bioavailability of copper ions in treated wood by using oxalate to pre-treat wood prior to colonization by a moderately copper-tolerant fungus. Copper-treated wood was treated with a gradient of sodium oxalate concentrations, rinsed thoroughly, and exposed in soil-block jars to an isolate of Serpula himantioides. Wood treated with copper ethanolamine was extremely effective in preventing decay by S. himantioides, but toxicity could repeatedly be overcome above a threshold level of oxalate pretreatment. In agar plates, copper-treated wood stimulated oxalate production by S. himantioides, but levels were less than those needed (>10 mM) to overcome copper in soil-block jars. This capacity to overcome copper using an oxalate pretreatment was absent in commercially available samples treated with co-biocide(s). Results demonstrate a useful relative measure of copper bioavailability, with potential to be modified for specific quantification.     

Colonisation of spruce roots by two interacting ectomycorrhizal fungi in wood ash amended substrates

Interactions between two ectomycorrhizal fungal species, Piloderma croceum Erikss. and Hjortst. and Piloderma sp. 1 (found to colonise spruce roots and wood ash granules in the field), were investigated in wood ash amended substrates. The comparative ability of these fungi to colonise roots of non-mycorrhizal spruce (Picea abies (L.) Karst.) seedlings was studied in relation to factorial combinations of wood ash and N fertilisation. Non-mycorrhizal spruce seedlings (bait seedlings) were planted together with spruce seedlings colonised by P. croceum or Piloderma sp. 1. The growth substrate was a sand-peat mixture with wood ash or no ash and supplied with two levels of N, so that four substrate combinations were obtained. Piloderma sp. 1 mycelia colonised around 60% of the fine roots of bait seedlings in ash treatments regardless of N level and around 20-26% in treatments without ash. P. croceum only colonised 8% of the root tips in the presence of ash but 56% of the root tips in the low-N treatment without ash. However, in the high-N treatment without ash the colonisation level was reduced to around 30%. Total numbers of root tips per seedling did not vary significantly between the treatments. Possible reasons for the competitive advantage of Piloderma sp. 1 in wood ash fertilised substrate are discussed.     

Removal of CCA from treated wood by oxalic acid extraction, steam explosion, and bacterial fermentation

Most preservative-treated wood produced and consumed in the United States is treated with toxic inorganic compounds containing copper, chromium, and arsenic. Because chromated copper arsenate (CCA) is fixed to the wood, CCA-treated wood has not been considered toxic or hazardous and it is currently disposed of in approved landfills. Growing public concern about environmental contamination from treated wood combined with the removal of greater quantities of CCA-treated wood from service have presented a disposal challenge for this fiber source. In this study, CCA-treated wood was processed by acid extraction, steam explosion, and bacterial fermentation and evaluated for removal of copper, chromium, and arsenic. Copper was the easiest to remove by these treatments and chromium the most resistant to removal. Exposing CCA-treated wood to steady-state bacterial growth by continuous culture with Bacillus licheniformis CC01 did not enhance removal of CCA components compared to standard mixed culture when acid extraction preceded bacterial fermentation. Nor did steam explosion, alone or in conjunction with acid extraction and bacterial fermentation, enhance removal of CCA components; the chromium and arsenic components resisted removal. Grinding CCA-treated wood chips into 20-mesh sawdust provided greater access to and removal of CCA components by all processes. However, grinding the chips was unnecessary if they were treated with acid prior to bacterial fermentation. Extraction with oxalic acid as a precursor to bacterial fermentation with B. licheniformis CC01 removed 90% copper (CuO), 80% chromium (CrO₃), and 100% arsenic (As₂O₅) from treated chips. The combination of acid extraction and bacterial fermentation removed 80–100% of these metals from CCA-treated wood. Received 15 December 1997/ Accepted in revised form 08 March 1998     

Ecosystem-level consequences of invasions by native species as a way to investigate relationships between evenness and ecosystem function

Biodiversity is currently undermined worldwide principally as a result of human activities. The irreversibility of species extinction has encouraged the research community to investigate the potential effect of declining species or functional group diversity and/or composition on ecosystem function since the beginning of the 1990s. However, while changes in relative abundance among species (i.e., evenness) are more frequent than extinction of species and are able to cause important changes in ecosystem function, most studies have curiously not examined thoroughly the potential role of that diversity component. The few small-scale experimental manipulations that have so far examined the relationship between evenness and ecosystem function have produced ambiguous results, sometimes indicating an effect on selected functions, and sometimes not. Because one reason for the inconsistency of the previous results may be scale-dependency issues, we propose here an alternative approach, investigation of this relationship directly at the system-level through the opportunity offered by field studies of ecosystem-level consequences of invasions by native species. Indeed, the specificities of changes in ecosystem structure induced by native invaders compared to exotic ones could constitute a useful tool to improve our understanding of the relationship between evenness and ecosystem function as well as to evaluate the importance of the spatial arrangement of species in the stability of ecosystems.