Tests were designed to determine moisture levels and inoculum amounts that maximized hemicellulose degradation. In preliminary test­ing (4) it was shown that 10.9 mg of P. ostreatus/g of dry stems was suf­ficient to allow successful competition of the inoculated fungus with indigenous microbes. However, 10.9 mg of P. ostreatus/g of dry stems and a gravimetric moisture content of 0.77 g of H2O/g of straw were too low to effect significant degradation of the straw in 12 wk (15). In those tests a proxy variable, the ratio of cellulose and hemicellulose compositions (C/H), was used to indicate the relative change in composition occurring from indigenous microbes and by P. ostreatus. This ratio was used because P. ostreatus has been shown to be somewhat selective for hemicellulose and lignin degradation vs cellulose degradation (7,8), while the indig­enous microbes were shown in uninoculated controls to be nonselective for one polysaccharide or the other (4).

Owing in part to the low and thus more uncertain measurements of the nonxylan carbohydrate components of hemicellulose (galactan, arabinan, and mannan), we decided to change the proxy variable to one exhibiting less variability as the result of measurement uncertainty. Two additional proxy ratios were assessed: the ratio of glucan and xylan com­positions (G/X) and an estimate of the relative degradation of xylan vs glucan (AX/AG). This "degradation ratio" was calculated from the esti­mated conversions, which assumed little change in the sum of ash, lignin, and extractives. Implicit in this is an assumption of minimal mineralization of lignin to CO2, and thus losses of lignin are assumed to be from depoly­merization to extractives; extractives would increase, keeping the sum of lignin and extractives constant. This allowed a closed mass balance to be estimated and the amounts of xylan and glucan degraded to be calculated on an initial weight basis.

A comparison of these ratios for the preliminary testing at 0-10.9 mg of P. ostreatus/g of stems and 0.77 g of H2O/g of stems is shown in Table 3. The majority of the glucan/xylan-based ratios had lower standard deviations than the corresponding cellulose/hemicellulose-based ratios, which was expected because xylan represents a greater fraction of the straw stems than galactan, arabinan, and mannan (Table 1). The relative changes in the three proxy variables were consistent among the data. For example, when C/H and G/X did not change significantly, indicating nonselective degradation of glucan and xylan, the estimated degradation ratio AX/AG was about 1. Similarly, when C/H and G/X exhibited only a small increase, AX/AG was only slightly larger than 1, while larger increases in C/H and G/X corre­sponded with large increases in AX/AG. This may provide some support for the assumption used to estimate AX/AG. The proxy ratio chosen for use was the degradation ratio AX/AG; with this change, the con-clusions of the pre­liminary study were unchanged, that is, P. ostreatus was shown to out- compete the indigenous organisms by 56 d. In addition, from 0 to 22 d the AX/AG ratios did not change significantly from 1.0, suggesting that under

the conditions tested, in the initial 22 d of culture P. ostreatus did not domi­nate degradation of the stems.