Small scale variation in decay rate within logs one year after felling: Effect of fungal community structure and moisture content

Abstract Fungal species composition, moisture content, percentage weight loss, and instantaneous decay rate (expressed by rate of CO₂ evolution) was assessed for a total of 186 8 cm³ cubes from 10 beech logs which had been decomposing on the forest floor for 14 months. There was considerable within and between branch variation in decay rate and water content. Water content at the time of sampling was not directly correlated with percentage weight loss or instantaneous decay rate, nor was it correlated with position in the log. However, wood occupied by Ascomycotina (other than Nectria ) tended to be drier than that occupied by Basidiomycotina. In particular wood occupied by Xylaria hypoxylon was drier than that occupied by all other species, although wood in which X. hypoxylon was replacing other fungi was wetter than when X. hypoxylon was alone. Variation in percentage weight loss could not be explained in terms of water content and fungal species composition at the time of sampling, but variation in instantaneous decay rate could. Thus, decay rate by Ascomycotina was significantly less ( P < 0.05) than by Basidiomycotina, and rate of CO₂ evolution from wood occupied by X. hypoxylon alone was significantly slower than from wood in which X. hypoxylon was replacing H. fragiforme or Nectria . The latter was partially correlated with water content but whether this is a cause and effect relationship is uncertain.