RESULTS 



The total quantity of soil organic materials varied sig- 

 nificantly between sites (table 2). In general, high-produc- 

 tivity, old-growth ecosystems had high organic reserves. 

 Low-productivity, old-growth and second-growth eco- 

 systems, particularly harsh ones, had low organic reserves. 

 The percentage distribution of organic fractions (litter, 

 humus, decayed wood) making up the organic mantle also 

 varied significantly. There were usually substantial 

 deposits of decayed wood in the forest floor on most sites. 



The total number of active ectomycorrhizal short root 

 tips also varied significantly between sites (table 3). As 

 with soil organic matter, the high-productivity, old-growth 

 stands had high numbers of active short root tips, and the 

 low-productivity, disturbed second-growth stands, par- 

 ticularly harsh ones, had low numbers of active tips. There 

 were many significant differences in percentage distribu- 

 tion of active ectomycorrhizal short root tips among the 

 soil fractions, both within and between sites. The most 

 striking general trends were reduced short root tips in the 

 deep mineral fraction and high numbers in the organic 

 fractions, particularly humus and decayed wood. Only two 

 sites had the highest mmiber of active short root tips in a 

 mineral fraction: old-growth ponderosa pine (site 8) and a 

 15-year-old stand of western larch (site 11). In both cases 

 it was the shallow (first 5 cm) mineral horizon that con- 

 tained most of the active tips (table 3). 



Soil wood as an ectomycorrhizal substratum is particu- 

 larly interesting. A number of factors indicate that the 

 association between decayed wood and mycorrhizal ac- 

 tivities may be of importance to host trees. Todd (1979) 



reports ectomycorrhizal fungi on Douglas-fir may be able 

 to break down certain organic materials directly, a means 

 for closed-cycle nutrient turnover. Selective concentration 

 of mycorrhizal inoculum in soil wood has been reported 

 (Kropp and Trappe 1982; Trappe 1965, 1962). Roots of 

 nonconiferous vegetation are seldom observed in soil wood 

 (Berntsen 1955; Harvey and others in press; Rowe 1955). 

 The apparent ability of mycorrhizal fungi to detoxify soil 

 phenolics (Zak 1971) may contribute to the ability of 

 conifer roots to thrive in decayed wood on and in forest 

 soils. Thus, soil wood provides a relatively competition-free 

 site for the growth of conifer feeder roots. In turn, this 

 provides a decided advantage to the conifers because they 

 are able to use this high-moisture material during drought 

 (Harvey and others 1978) and on dry sites (Harvey and 

 others 1979). Also, it is now apparent that some higher 

 plants have hydrotropic roots (Jaffe and others 1985). 

 Thus, the moisture contained in soil wood may be the 

 primary reason for the concentration of conifer roots 

 therein. 



Although the number of samples taken on most of the 

 sites was not sufficient to show significant differences in 

 distribution of ectomycorrhizal activities among organic 

 matter classes (table 4), the trend toward low numbers of 

 short roots in the highest organic content class (> 45 per- 

 cent of the core) was striking. This was particularly evi- 

 dent in moderate- to low-productivity, old-growth stands 

 and in second-growth sites. This trend is likely related to 

 soil moisture availability. Periodic rainfall on these sites 

 may not be enough to wet deep organic matter deposits 

 sufficiently to maintain them above the permanent wilting 

 point, particularly during the normally dry growing 



Table 2 — Quantity and distribution of soil organic components from plots sampled 



Distribution of organic matter 

 in forest floor 



number and 

 acronym 



Total organic matter in 

 soil core (x L/core) 



Litter 



Humus 



Decayed wood 





Liters 





Percent 



Old-growth^ 











1(WH-M) 



20.82" 



3^23 



38'' 



51" 



2(SAF-M) 



.77" 



7^ 



45" 



48" 



4(WH-I) 



.54" 





30" 



58" 



3(DF-M) 



.50" 



6^ 



SS"^ 



35" 



5(WWP-I) 



.43" 



30= 



19" 



51^ 



8(PP-W) 



.38" 



31 = 



68" 



2= 



6(GF-I) 



.32>' 



25= 



61" 



14= 



7(SAF-WY) 



.15^ 



34= 



52" 



14^ 



Second-growth 











lO(LPP-i) 



.42" 



19= 



58" 



23^ 



9(MIX-i) 



.39" 



19= 



46" 



36^ 



1 1 (WL-y) 



.32" 



21 = 



41" 



39=" 



12(DF-i) 



.26" 



22= 



42" 



35=" 



13(PP-i) 



.12^ 



27= 



58" 



15^ 



14(LPP-y) 



.12^ 



46= 



40= 



14" 



''See table 1 for explanation of abbreviations. 



^Average includes all organic matter-containing strata. Differing letters indicate significant dif- 

 ferences down column (w-z), a = 0.05. ANOVA. Duncan's multiple range test. 



^Differing letters (a-c) indicate significant differences (a = 0.05) witfiin treatments, between 

 individual strata, detected by two-sided t-test on actual volume measurements. 



4 



