Decomposers, Bacteria, and Microbenthos 357 



These length measures in Pond C can be converted into biomass by 

 multiplication with 0.16 (gdw) cm ' (the bulk density of surface sediments 

 in Pond C, Table 4-1) and with 1 .0 x 10 ' mg m ' (hyphal dry weight per 

 meter, from Bunnell et al. 1980). After further conversions to a square 

 meter basis, the data become 1600 mg m " at 1-2 cm and 220 mg at 6-7 

 cm depth. The assumption of a linear decrease with depth gives 7070 mg 

 m '" in the top 8 cm or 3500 mg C m^^ 



Based on this single measurement of 3500 mg C m \ it would appear 

 that fungal hyphae make up 70% of the microbial biomass (in Figure 1-5 

 there are 1 500 mg C m ^ of bacteria). Given the changes expected in both 

 the bacteria (Figure 8-1) and the fungi (Figure 8-6 in Brown et al. 1980) 

 this fungal portion may vary greatly. For example, the bacterial biomass 

 data is based upon a volume of 0.1 ^m^ per cell. Rublee et al. (1977) found 

 that the mean cell size in sediments was 0.2 nm^ (this would double our 

 biomass). Yet, the difference between these two volumes is equivalent to 

 deciding that a bacterial cell has a diameter of 0.75 ^m instead of 0.60 ^m. 

 In the absence of any other fungal data, the arguments about the 

 importance of microbes in this book have used only the bacterial data. 

 However, even if fungi were to be included, the conclusions would not 

 change. 



DECOMPOSITION OF MACROPHYTES* 



Methods 



On 18 June 1972, leaves of Carex were collected for litterbag 

 experiments and separated into green, yellow, and brown fractions. The 

 green fraction consisted of live leaves that' were produced late in the 

 previous season (leaf numbers 5, 6, and 7) but that retained all or a part of 

 their chlorophyll. The yellow fraction was leaves which died at the end of 

 the previous season, while the brown leaves were dead for the entire 

 previous season or perhaps for several seasons. After separation, the leaves 

 were air dried for 6 days, and then weighed amounts (88 to 600 mg) were 

 placed in 7.5xl5.0-cm litterbags made of 20-Mm Nitex netting. We also 

 tested oven drying at 105°C; it gave an additional loss of 4.4% from green 

 leaves, 5.0% from yellow leaves, and 5.5% from brown leaves (Hobbie 

 1973). These 20-Mm mesh bags were submerged in Pond B during the first 

 week of July 1972; three litterbags of each fraction were removed on each 

 subsequent sampling date which occurred after 1, 2, 4, 8, and 58 weeks. 



In a similar fashion, yellow leaves were also placed in 1-mm mesh 

 bags. These mesh bags were incubated along with 20-Mm mesh bags in the 



*T. Traaen 



