Ecological Studies on Microbial Deterioration of Untreated and Copper-chrome-arsenate Treated Wood Exposed to the Soil

Abstract

Respirometry was employed to quantify the activity of microorganisms invading sapwood buried in the soil. Activity was related to the effect of extractable materials on the rate of colonisation of sapwoods of Pinus sylvestris (Linn) and Tilia vulgaris (Hayne). Extracted wood samples exposed to the soil respired more than those not extracted. Oxygen uptake in extracted blocks impregnated with some simple sugars and amino acids was greater than in control blocks. The ecological relevance of these studies was described in relation to early colonisation. Differences in the subsequent decay of wood blocks as determined by weight loss was related to wood porosity and lignin content. The effect of partial delignification of wood on the rate of colonisation and decay was investigated. Microscopy and respirometry were used to study the distribution of microbial activity in the invaded wood. In scots pine, respiratory activity as well as cavity formation was found to be greatest in the latewood. No preferential decay of the early or latewood was found in lime but the presence of both erosion form of attack and typical soft rot cavities were noted. In CCA-treated wood oxygen uptake was positively correlated with weight loss both after four and eight weeks of soil burial. This correlation, however, was less perfect after eight weeks. The toxic limit of CCA in wood was found to be dependent upon the period of incubation. CCA inhibited cellulase activity in pure cultures and it was suggested that cellulase inhibition could be one of the modes of action of the preservative. Changes in pH, moisture content and respiratory activity in wood at different depths with period of incubation were investigated. Treated wood extracted with culture filtrates of selected micro-fungi decayed more than controls and it was suggested that these fungi may also account for loss of the preservative from wood.